对mysql数据库表优化，优化代码提升性能 （简易新闻 七）

第一步创建索引

为那些经常要查询的字段设置索引如：
category，其中设置一个复合索引（title,category）为后面实现精确查询埋下伏笔
关于索引，复合索引，全文检索等可以去看 mysql数据库进阶学习 一
使用的数据库为mysql
输入如下sql语句（单索引category）：

alter table news_info add index in_c(category);

输入如下sql语句（复合索引）：

alter table news_info add index (title,category);

效果如下：

其中第一个为单索引，第二个箭头为复合索引，第三个箭头为全文检索（这里暂时不需要），看到这里（如果你细心看的话不难发现，没有title的单索引）
这里又和复合索引有很大关系,我们新建的复合索引title(title,category)使用功能包括实现单索引(title),复合（title,category）查询。

优化查询语句

优化子查询（使用JOIN连接查询）
修改UserFavoriteActivity.java

package com.example.frametest.UserMode;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;

import com.example.frametest.R;
import com.example.frametest.WebActivity;
import com.example.frametest.json.NewsBean;
import com.example.frametest.tools.DBOpenHelper;
import com.example.frametest.tools.MyApplication;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class UserFavoriteActivity extends AppCompatActivity {
    private ListView listView;
    private List<NewsBean.ResultBean.DataBean> newList = new ArrayList<>();
    NewsBean.ResultBean.DataBean dataBean;
    String phone_userfavorite;
    private static final int NewsFav_List = 6;
    private TextView textView;
    @SuppressLint("HandlerLeak")
    private Handler newsFavHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case NewsFav_List:
                    NewsInfoAdapter adapter = new NewsInfoAdapter(UserFavoriteActivity.this,R.layout.item_layout_news,newList);
                    Log.d("传入数据后", String.valueOf(newList.size()));
                    listView.setAdapter(adapter);
                    adapter.notifyDataSetChanged();
                    break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_favorite);
        initNews();
        listView = (ListView) findViewById(R.id.list_news);
        phone_userfavorite = MyApplication.getMoublefhoneUser();
        System.out.println("收藏页面是否传值"+phone_userfavorite);
        Toolbar toolbar = (Toolbar) findViewById(R.id.userFavorite_toolbar);
        toolbar.setTitle("我的收藏");
        setSupportActionBar(toolbar);
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null){
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeAsUpIndicator(R.drawable.ic_chevron_left);
        }
    }
    private void initNews() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                Connection conn = null;
                conn = (Connection) DBOpenHelper.getConn();
                //这里优化子查询
                String sql = "select title,url from news_info LEFT JOIN user_collect on news_info.uniquekey=user_collect.news_id where user_collect.user_phone= ?";
                PreparedStatement pstmt;
                try {
                    String  num = phone_userfavorite;
                    pstmt = (PreparedStatement) conn.prepareStatement(sql);
                    pstmt.setString(1,num);
                    ResultSet rs = pstmt.executeQuery();
                    while (rs.next()){
                        rs.getString(1);
                        NewsBean.ResultBean.DataBean dataBean = new NewsBean.ResultBean.DataBean();
                        dataBean.setTitle(rs.getString(1));
                        dataBean.setUrl(rs.getString(2));
                        newList.add(dataBean);
                    }
                    pstmt.close();
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                //此处优化
                //
                Message msg = newsFavHandler.obtainMessage();
                msg.what=NewsFav_List;
                newsFavHandler.sendMessage(msg);
            }
        }).start();

    }

    @SuppressLint("MissingSuperCall")
    @Override
    protected void onStart() {
        super.onStart();
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                NewsBean.ResultBean.DataBean dataBean = newList.get(position);
                String url = dataBean.getUrl();
                Intent intent = new Intent(UserFavoriteActivity.this,WebActivity.class);
                intent.putExtra("url",url);
                startActivity(intent);
            }
        });
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case android.R.id.home:
                UserFavoriteActivity.this.finish();
                break;
        }
        return true;
    }
}

判断条件中的user_phone=13115231059改为。。。=‘1311’

优化代码

优化方法：修改Handler通信。
即把原来的

Message msg =new Message();

替换为

Message msg = handler..obtainMessage();  //方法

修改MainActivity.java

package com.example.frametest;

import android.annotation.SuppressLint;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Handler;
import android.os.Message;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.design.widget.NavigationView;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.GravityCompat;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.example.frametest.UserMode.LoginActivity;
import com.example.frametest.UserMode.User;
import com.example.frametest.UserMode.UserFavoriteActivity;
import com.example.frametest.UserMode.User_DataActivity;
import com.example.frametest.tools.DBOpenHelper;
import com.example.frametest.tools.MyApplication;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import de.hdodenhof.circleimageview.CircleImageView;

public class MainActivity extends AppCompatActivity {
    private android.support.v7.widget.Toolbar toolbar;
    private DrawerLayout mDrawerLayout;
    private NavigationView navigationView;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    private List<String> list;
    private TextView tvhuoqu,tvName;
    String phonenumber,userName;
    private static final int USER_LOOK_NAME = 0;
    @SuppressLint("HandlerLeak")
    private Handler userFeedHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            String admin_title,admin_url,user_name;
            switch (msg.what){
                case USER_LOOK_NAME:
                    User user = (User) msg.obj;
                    user_name =user.getUser_name();
                    tvName = (TextView) findViewById(R.id.text_username);
                    tvName.setText(user_name);
                    break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toolbar =  findViewById(R.id.toolbar);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout); //获取抽屉布局
        navigationView = (NavigationView) findViewById(R.id.nav_design);//获取菜单控件实例
        View v = navigationView.getHeaderView(0);
        CircleImageView circleImageView =(CircleImageView) v.findViewById(R.id.icon_image);
        tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        viewPager = (ViewPager) findViewById(R.id.viewPager);
        list = new ArrayList<>();
        tvhuoqu = (TextView) findViewById(R.id.text_huoqu);
    }

    @Override
    protected void onStart() {
        super.onStart();
       /* toolbar.setLogo(R.drawable.icon);//设置图片logo,你可以添加自己的图片*/
        toolbar.setTitle("简易新闻");
        setSupportActionBar(toolbar);
        ActionBar actionBar = getSupportActionBar();
        if (actionBar !=null){
            //通过HomeAsUp来让导航按钮显示出来
            actionBar.setDisplayHomeAsUpEnabled(true);
            //设置Indicator来添加一个点击图标
            actionBar.setHomeAsUpIndicator(R.drawable.ic_menu_24dp);
        }
        navigationView.setCheckedItem(R.id.nav_call);//设置第一个默认选中
        navigationView.setNavigationItemSelectedListener(new  NavigationView.OnNavigationItemSelectedListener() {
            //设置菜单项的监听事件
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                mDrawerLayout.closeDrawers();
                switch (menuItem.getItemId()) {
                    case R.id.nav_call:
                        phonenumber = MyApplication.getMoublefhoneUser();
                        //通过判断手机号是否存在，来决定是进入编辑资料页面还是进入登陆页面
                        if (phonenumber != null){
                            Intent unIntent = new Intent(MainActivity.this,User_DataActivity.class);
                            startActivity(unIntent);
                        } else {
                            Intent exitIntent = new Intent(MainActivity.this,LoginActivity.class);
                            startActivity(exitIntent);
                        }
                        break;
                    case R.id.nav_friends:
                        //
                        break;
                    case R.id.nav_location:
                        Toast.makeText(MainActivity.this, "你点击了发布新闻，下步实现", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.nav_favorite:
                        phonenumber = MyApplication.getMoublefhoneUser();
                        if (phonenumber != null){
                            Intent userFavIntent = new Intent(MainActivity.this,UserFavoriteActivity.class);
                            startActivity(userFavIntent);
                        } else {
                            Intent exitIntent = new Intent(MainActivity.this,LoginActivity.class);
                            startActivity(exitIntent);
                        }
                        break;
                    case R.id.nav_settings:
                        Toast.makeText(MainActivity.this,"需要做出登出功能，可扩展夜间模式，离线模式等,检查更新",Toast.LENGTH_LONG).show();
                        break;
                    case R.id.nav_exit:
                        Intent intent = new Intent(MainActivity.this,LoginActivity.class);
                        startActivity(intent);
                        break;
                    default:
                }
                return true;
            }
        });
        list.add("头条");
        list.add("社会");
        list.add("国内");
        list.add("国际");
        list.add("娱乐");
        list.add("体育");
        list.add("军事");
        list.add("科技");
        list.add("财经");
       /* viewPager.setOffscreenPageLimit(1);*/
        viewPager.setAdapter(new FragmentStatePagerAdapter(getSupportFragmentManager()) {
            //得到当前页的标题，也就是设置当前页面显示的标题是tabLayout对应标题

            @Nullable
            @Override
            public CharSequence getPageTitle(int position) {
                return list.get(position);
            }
            @Override
            public Fragment getItem(int position) {
                NewsFragment newsFragment = new NewsFragment();
                //判断所选的标题，进行传值显示
                Bundle bundle = new Bundle();
                if (list.get(position).equals("头条")){
                    bundle.putString("name","top");
                }else if (list.get(position).equals("社会")){
                    bundle.putString("name","shehui");
                }else if (list.get(position).equals("国内")){
                    bundle.putString("name","guonei");
                }else if (list.get(position).equals("国际")){
                    bundle.putString("name","guoji");
                }else if (list.get(position).equals("娱乐")){
                    bundle.putString("name","yule");
                }else if (list.get(position).equals("体育")){
                    bundle.putString("name","tiyu");
                }else if (list.get(position).equals("军事")){
                    bundle.putString("name","junshi");
                }else if (list.get(position).equals("科技")){
                    bundle.putString("name","keji");
                }else if (list.get(position).equals("财经")){
                    bundle.putString("name","caijing");
                }else if (list.get(position).equals("时尚")){
                    bundle.putString("name","shishang");
                }
                newsFragment.setArguments(bundle);
                return newsFragment;
            }

            @NonNull
            @Override
            public Object instantiateItem(@NonNull ViewGroup container, int position) {
                NewsFragment newsFragment = (NewsFragment)  super.instantiateItem(container, position);

                return newsFragment;
            }

            @Override
            public int getItemPosition(@NonNull Object object) {
                return FragmentStatePagerAdapter.POSITION_NONE;
            }

            @Override
            public int getCount() {
                return list.size();
            }
        });
        //TabLayout要与ViewPAger关联显示
        tabLayout.setupWithViewPager(viewPager);
        String inputText = load();
        if (!TextUtils.isEmpty(inputText)){
            System.out.println("________)))))))");
            System.out.println("________)))))))");
            System.out.println(phonenumber);
            phonenumber =inputText;
            MyApplication.setMoublefhoneUser(phonenumber);
        }



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        //获取toolbar菜单项
        getMenuInflater().inflate(R.menu.toolbar,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            //R.id.home修改导航按钮的点击事件为打开侧滑栏
            case android.R.id.home:
                if (MyApplication.getInstance().getMoublefhoneUser() != null){
                    phonenumber = MyApplication.getInstance().getMoublefhoneUser();
                }
                mDrawerLayout.openDrawer(GravityCompat.START);  //打开侧滑栏
                tvhuoqu = (TextView) findViewById(R.id.text_huoqu);
                tvhuoqu.setText(phonenumber);
                //用户开启侧滑栏时，查询数据库对应手机号的用户名，并显示在侧滑栏头部
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Connection conn = null;
                        conn = (Connection) DBOpenHelper.getConn();
                        String sql = "select user_name from user_info where  user_phone ='"+phonenumber+"'";
                        Statement pstmt;
                        try {
                            pstmt = (Statement) conn.createStatement();
                            ResultSet rs = pstmt.executeQuery(sql);
                            while (rs.next()){
                                User user = new User();
                                user.setUser_name(rs.getString(1));
                                //此处优化方法，去掉以前的new Message()这样会不断地新增一个Handle增加内存空间响应时间
                                //
                                Message msg = userFeedHandler.obtainMessage();
                                msg.what=USER_LOOK_NAME;
                                msg.obj = user;
                                userFeedHandler.sendMessage(msg);
                            }
                            pstmt.close();
                            conn.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                }).start();
                break;
            case R.id.userFeedback:
                final EditText ed =new EditText(MainActivity.this);
                AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this);
                dialog.setTitle("用户反馈");
                dialog.setView(ed);
                dialog.setCancelable(false);
                dialog.setPositiveButton("确认", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                       //添加点击事件
                    }
                });
                dialog.setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });
                dialog.show();
                break;
            case R.id.userExit:
                Toast.makeText(this,"ni click 退出",Toast.LENGTH_SHORT).show();
                break;
            default:

        }
        return true;
    }
    public String load() {
        FileInputStream in = null;
        BufferedReader reader = null;
        StringBuilder content = new StringBuilder();
        try {
            in = openFileInput("data");
            System.out.println("是否读到文件内容"+in);
            reader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null){
                content.append(line);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (reader != null){
                try {
                    reader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return content.toString();
    }
}

修改UserFavoriteActivity.java

package com.example.frametest.UserMode;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;

import com.example.frametest.R;
import com.example.frametest.WebActivity;
import com.example.frametest.json.NewsBean;
import com.example.frametest.tools.DBOpenHelper;
import com.example.frametest.tools.MyApplication;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class UserFavoriteActivity extends AppCompatActivity {
    private ListView listView;
    private List<NewsBean.ResultBean.DataBean> newList = new ArrayList<>();
    NewsBean.ResultBean.DataBean dataBean;
    String phone_userfavorite;
    private static final int NewsFav_List = 6;
    private TextView textView;
    @SuppressLint("HandlerLeak")
    private Handler newsFavHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case NewsFav_List:
                    NewsInfoAdapter adapter = new NewsInfoAdapter(UserFavoriteActivity.this,R.layout.item_layout_news,newList);
                    Log.d("传入数据后", String.valueOf(newList.size()));
                    listView.setAdapter(adapter);
                    adapter.notifyDataSetChanged();
                    break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_favorite);
        initNews();
        listView = (ListView) findViewById(R.id.list_news);
        phone_userfavorite = MyApplication.getMoublefhoneUser();
        System.out.println("收藏页面是否传值"+phone_userfavorite);
        Toolbar toolbar = (Toolbar) findViewById(R.id.userFavorite_toolbar);
        toolbar.setTitle("我的收藏");
        setSupportActionBar(toolbar);
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null){
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeAsUpIndicator(R.drawable.ic_chevron_left);
        }
    }
    private void initNews() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                Connection conn = null;
                conn = (Connection) DBOpenHelper.getConn();
                String sql = "select title,url from news_info where uniquekey in(  select news_id from user_collect  where user_phone = ?)";
                PreparedStatement pstmt;
                try {
                    String  num = phone_userfavorite;
                    System.out.println("^^^^^^^^^");
                    System.out.println("^^^^^^^^^");
                    System.out.println("huoqu手机号内容是"+num);
                    pstmt = (PreparedStatement) conn.prepareStatement(sql);
                    pstmt.setString(1,num);
                    ResultSet rs = pstmt.executeQuery();
                    while (rs.next()){
                        rs.getString(1);
                        NewsBean.ResultBean.DataBean dataBean = new NewsBean.ResultBean.DataBean();
                        dataBean.setTitle(rs.getString(1));
                        dataBean.setUrl(rs.getString(2));
                        newList.add(dataBean);
                    }
                    pstmt.close();
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
                //此处优化
                //
                Message msg = newsFavHandler.obtainMessage();
                msg.what=NewsFav_List;
                newsFavHandler.sendMessage(msg);
            }
        }).start();

    }

    @SuppressLint("MissingSuperCall")
    @Override
    protected void onStart() {
        super.onStart();
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                NewsBean.ResultBean.DataBean dataBean = newList.get(position);
                String url = dataBean.getUrl();
                Intent intent = new Intent(UserFavoriteActivity.this,WebActivity.class);
                intent.putExtra("url",url);
                startActivity(intent);
            }
        });
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case android.R.id.home:
                UserFavoriteActivity.this.finish();
                break;
        }
        return true;
    }
}

修改User_DataActivity.java

package com.example.frametest.UserMode;

import android.Manifest;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.content.ContentUris;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Build;
import android.os.Handler;
import android.os.Message;
import android.provider.DocumentsContract;
import android.provider.MediaStore;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
import com.example.frametest.R;
import com.example.frametest.tools.DBOpenHelper;
import com.example.frametest.tools.MyApplication;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class User_DataActivity extends AppCompatActivity {
    private ImageView imageView_user;
    public static final int CHOOSE_USER_TOUX =11;
    public static final int USER_SETTINGS_NAME =12;
    public static final int USER_UPDATE_NAME =13;
    private TextView tv_user_photo,tv_nc,tv_nc_fb;
    String user_setting_phone;
    String input_userName;
    @SuppressLint("HandlerLeak")
    private Handler userSettingsHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            String admin_title,admin_url;
            switch (msg.what){
                case USER_SETTINGS_NAME:
                    Toast.makeText(User_DataActivity.this,"用户名为空或不存在！",Toast.LENGTH_SHORT).show();
                    break;
                case USER_UPDATE_NAME:
                    tv_nc_fb.setText(input_userName);
                    break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user__data);
        user_setting_phone = MyApplication.getMoublefhoneUser();
        Toolbar uToolbar = (Toolbar) findViewById(R.id.userData_toolbar);
        tv_user_photo = (TextView)findViewById(R.id.tv_user_photo);
        imageView_user = (ImageView)findViewById(R.id.imageView_user);
        tv_nc = (TextView)findViewById(R.id.tv_nc);
        tv_nc_fb = (TextView) findViewById(R.id.tv_nc_fb);
        uToolbar.setTitle("个人信息");
        setSupportActionBar(uToolbar);
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null){
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeAsUpIndicator(R.drawable.ic_chevron_left);
        }
    }

    @Override
    protected void onStart() {
        super.onStart();
        tv_user_photo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ContextCompat.checkSelfPermission(User_DataActivity.this,Manifest.permission.WRITE_EXTERNAL_STORAGE) !=PackageManager.PERMISSION_GRANTED){
                    ActivityCompat.requestPermissions(User_DataActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
                }else {
                    openAlbum();
                }
            }
        });
        tv_nc.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final EditText editText =new EditText(User_DataActivity.this);
                AlertDialog.Builder alog = new AlertDialog.Builder(User_DataActivity.this);
                alog.setTitle("输入用户名");
                alog.setView(editText);
                alog.setCancelable(false);
                alog.setPositiveButton("提交", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        new Thread(new Runnable() {
                            @Override
                            public void run() {
                                input_userName = editText.getText().toString();
                                if ("".equals(input_userName) || input_userName == null) {
                                    //此处优化
                                    //
                                    Message msg = userSettingsHandler.obtainMessage();
                                    msg.what =USER_SETTINGS_NAME;
                                    userSettingsHandler.sendMessage(msg);
                                } else {
                                    Connection conn = null;
                                    conn = (Connection) DBOpenHelper.getConn();
                                    String sql = "update user_info set user_name='"+input_userName+"' where user_phone='"+user_setting_phone+"'";
                                    int i = 0;
                                    PreparedStatement pstmt;
                                    try {
                                        pstmt = (PreparedStatement) conn.prepareStatement(sql);
                                        i = pstmt.executeUpdate();
                                        pstmt.close();
                                        conn.close();
                                        //此处优化
                                        //
                                        Message msg = userSettingsHandler.obtainMessage();
                                        msg.what = USER_UPDATE_NAME;
                                        userSettingsHandler.sendMessage(msg);
                                    } catch (SQLException e) {
                                        e.printStackTrace();
                                    }
                                }
                            }
                        }).start();
                    }
                });
                alog.setNegativeButton("取消", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });
                alog.show();


            }
        });
    }
    private void openAlbum() {
        Intent mIntent = new Intent("android.intent.action.GET_CONTENT");
        mIntent.setType("image/*");
        startActivityForResult(mIntent,CHOOSE_USER_TOUX);
    }
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode){
            case 1:
                if (grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED){
                    openAlbum();
                }else {
                    Toast.makeText(this,"you denied the permission",Toast.LENGTH_SHORT).show();
                }
                break;
            default:
        }
    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        switch (requestCode){
            case CHOOSE_USER_TOUX:
                if (resultCode == RESULT_OK) {
                    if (Build.VERSION.SDK_INT >= 19){
                        handleImageOnKiKat(data);
                    }else {
                        handleImageBeforeKiKat(data);
                    }
                }
                break;
        }
    }
    @TargetApi(Build.VERSION_CODES.KITKAT)
    private void handleImageOnKiKat(Intent data) {
        String imagePath = null;
        Uri uri = data.getData();
        if (DocumentsContract.isDocumentUri(this,uri)){
            String docId = DocumentsContract.getDocumentId(uri);
            if ("com.android.providers.media.documents".equals(uri.getAuthority())){
                String id = docId.split(":")[1];
                String selection = MediaStore.Images.Media._ID + "=" + id;
                imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,selection);
            }else if ("com.android.providers.downloads.documents".equals(uri.getAuthority())){
                Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"),Long.valueOf(docId));
                imagePath = getImagePath(contentUri,null);
            }
        } else if ("content".equalsIgnoreCase(uri.getScheme())){
            //如或是content类型的URI就使用普通方法处理
            imagePath = getImagePath(uri,null);

        } else if ("file".equalsIgnoreCase(uri.getScheme())){
            //如果是file类型的直接获取图片路径就行
            imagePath = uri.getPath();
        }
        diplayImage(imagePath); //根据路径显示图片
    }
    private void handleImageBeforeKiKat(Intent data) {
        Uri uri = data.getData();
        String imagePath = getImagePath(uri,null);
        diplayImage(imagePath);
    }

    private String getImagePath(Uri uri, String selection) {
        String path = null;
        //通过Uri和selection来获取真实的图片路径
        Cursor cursor = getContentResolver().query(uri,null,selection,null,null);
        if (cursor != null){
            if (cursor.moveToFirst()){
                path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
            }
            cursor.close();
        }
        return path;
    }

    private void diplayImage(String imagePath) {
        if (imagePath != null){
            Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
            imageView_user.setImageBitmap(bitmap);
            int a =10;
        } else {
            Toast.makeText(this,"failed to get image",Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()){
            case android.R.id.home:
                User_DataActivity.this.finish();
                break;
        }
        return true;
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Intent intent = new Intent();
        finish();
    }
}

今天就讲到这里了，欢迎批评与指正！，后面如果可以进一步对数据库或者代码优化的，可能会另起一篇。关于整个app的制作可以看 android新闻app 。
下一篇将会对活动栈优化。