Android--小小记事本

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Android–小小记事本

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1：文本数据的存储
2：图片数据存储
3：SQlite的创建
4：数据listview列表的显示

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---

activity_main.xml布局文件

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.jl.festival_sms.MainActivity">

    <TextView
        android:id="@+id/tv_titile"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="备忘录"
        android:textSize="25sp"
        android:textColor="#000000"
        android:gravity="center"
        android:background="@color/main_color"
        android:padding="5dp"
        />

    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:layout_margin="5dp"
        android:background="#FFFFFF"
        >

    </ListView>

    <Button
        android:id="@+id/bt_add"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:padding="5dp"
        android:text="添加备忘录"
        />

</LinearLayout>

---

edittext_activity.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">


        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="编辑"
            android:padding="5dp"
            android:textSize="25dp"
            android:gravity="center"
            android:background="@color/main_color"
            />

        <EditText
            android:id="@+id/et_center"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:gravity="start"
            android:textSize="18sp"
            android:layout_margin="5dp"
            />

    <TextView
        android:id="@+id/tv_data"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:textColor="#807c7c"
        android:text="时间"
        />

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <Button
            android:id="@+id/bt_ok"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="保存"
            />
        <Button
            android:id="@+id/bt_cancel"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="取消"
            />

    </LinearLayout>
</LinearLayout>

---

item.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:singleLine="true"
        android:textSize="20sp"
        android:textColor="#000"
        android:text="标题" />

    <TextView
        android:id="@+id/tv_date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="时间" />

</LinearLayout>

---

数据库文件

定义了数据库中的表明，以及用到的数列，因为此项目仅对文字进行了保存，因此对变量都定义成static final类型的，使得名称和列名不可被更改。

在继承SQLiteDatabase 的时候不光需要实现 ：

onUpgrade(SQLiteDatabse dv, int oldVersion,int new Version)：当打开数据库时传入的版本号与当前的版本号不同时会调用该方法。

---

并且还需要调用其父类构造器 context是上下文，name为数据库的名字，Cursor的工厂类以及版本号

 public MySQLiteHelper(Context context, String name, CursorFactory factory,  
            int version) {  
        super(context, name, factory, version);  
    }  

---

数据库文件具体代码：

package com.example.jl.festival_sms;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

/**
 * Created by jl on 2017/7/27.
 */

public class DBHelper extends SQLiteOpenHelper {
    public  static  final  String TABLE_NAME="note";
    public static final String ID = "id";
    public  static  final  String CONTENT = "content";
    public  static  final  String DATE = "date";


    public static final String SQL="CREATE TABLE " + TABLE_NAME + " (" + ID
            + " INTEGER PRIMARY KEY AUTOINCREMENT," + CONTENT
            + " TEXT NOT NULL," + DATE + " TEXT NOT NULL)";

    public DBHelper(Context context){
        super(context,TABLE_NAME,null,1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }


}

---

主界面代码的实现

SQLiteDatabase  ： 获取数据库对象 
ContentValues   ： 数据库的操作的时候需要ContentValues类  也是一个key对应一个数据
Bundle          ： 两个activity之间的通讯可以通过bundle类来实现，bundle类中加入数据（key-
                    value的形式，另一个activity里面取数据的时候，就要用到key，找出对应的
                    value）。加入到intent的当中使用intent.putExtras（）方法。

package com.example.jl.festival_sms;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.app.AlertDialog.Builder;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemLongClickListener;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public class MainActivity extends AppCompatActivity implements OnItemClickListener, OnItemLongClickListener {

    private ListView mListView;
    private Button mButton;
    private TextView tv_content;

    private DBHelper dbHelper;
    private SQLiteDatabase DB;
    private SimpleAdapter simple_adapter;
    private List<Map<String, Object>> dataList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        init();
    }

    //初始化视图
    private void init() {
        tv_content = (TextView) findViewById(R.id.tv_content);
        mListView = (ListView) findViewById(R.id.lv);
        mButton = (Button) findViewById(R.id.bt_add);
        dataList = new ArrayList<Map<String, Object>>();
        dbHelper = new DBHelper(this);
        DB = dbHelper.getReadableDatabase();

        mListView.setOnItemClickListener(this);
        mListView.setOnItemLongClickListener(this);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this,EditActivity.class);
                Bundle bundle = new Bundle();
                bundle.putString("info","");
                bundle.putInt("enter_state",0);
                intent.putExtras(bundle);
                startActivity(intent);
            }
        });
    }

    //当页面重新打开的时候
    @Override
    protected void onStart() {
        super.onStart();
        //刷新页面
        RefreshNotesList();
    }

    private void RefreshNotesList() {
        //如果dataList已经有的内容，全部删掉
        //并且更新simp_adapter
        int size = dataList.size();
        if(size>0){
            dataList.removeAll(dataList);
            simple_adapter.notifyDataSetChanged();
        }

        //从数据库读取信息
        Cursor cursor = DB.query("note", null, null, null, null, null, null);
        startManagingCursor(cursor);
        while (cursor.moveToNext()){
            String name = cursor.getString(cursor.getColumnIndex("content"));
            String date = cursor.getString(cursor.getColumnIndex("date"));
            Map<String,Object> map = new HashMap<>();
            map.put("tv_content",name);
            map.put("tv_date",date);
            dataList.add(map);
        }

        simple_adapter =new SimpleAdapter(this,dataList,R.layout.item,new String[]{"tv_content","tv_date"}
                                            ,new int[]{R.id.tv_content,R.id.tv_date});
        mListView.setAdapter(simple_adapter);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        String content = mListView.getItemAtPosition(position) + "";
        String content1 = content.substring(content.indexOf("=") + 1, content.indexOf(","));
        Intent Intent = new Intent(MainActivity.this, EditActivity.class);
        Bundle bundle = new Bundle();
        bundle.putString("info", content1);
        bundle.putInt("enter_state", 1);
        Intent.putExtras(bundle);
        startActivity(Intent);
    }

    @Override
    public boolean onItemLongClick(AdapterView<?> parent, View view, final int position, long id) {
        Builder builder = new Builder(this);
        builder.setTitle("删除该日志");
        builder.setMessage("确认删除吗？");
        builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                //获取listview中此个item中的内容
                //删除该行后刷新listview的内容
                String content = mListView.getItemAtPosition(position) + "";
                String content1 = content.substring(content.indexOf("=") + 1,
                        content.indexOf(","));
                DB.delete("note", "content = ?", new String[]{content1});
                RefreshNotesList();
            }
        });
        builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
            }
        });
        builder.create();
        builder.show();
        return true;
    }
}

编辑界面

package com.example.jl.festival_sms;

import android.app.Activity;
import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * Created by jl on 2017/7/27.
 */

public class EditActivity extends Activity implements View.OnClickListener {

    private TextView tv_date;
    private EditText et_content;
    private Button bt_ok;
    private Button bt_cancel;
    private DBHelper DBHelper;
    public int ENTER_STATIC = 0;//用来区分是新建一个note还是更改原来的note
    public String last_content;//用来获取edittext内容

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.edittext_activity);

        init();
    }

    private void init() {
        tv_date = (TextView) findViewById(R.id.tv_data);
        et_content = (EditText) findViewById(R.id.et_center);
        bt_ok = (Button) findViewById(R.id.bt_ok);
        bt_cancel = (Button) findViewById(R.id.bt_cancel);
        DBHelper = new DBHelper(this);

        //获取此时时刻时间
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
        String dateString = sdf.format(date);
        tv_date.setText(dateString);


        //接收内容和id
        Bundle myBundle = this.getIntent().getExtras();
        last_content = myBundle.getString("info");
        ENTER_STATIC = myBundle.getInt("enter_state");
        et_content.setText(last_content);
        //设置其点击事件
        bt_ok.setOnClickListener(this);
        bt_cancel.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.bt_ok:
                SQLiteDatabase db =DBHelper.getReadableDatabase();
                // 获取输入框的内容
                String mesg = et_content.getText().toString();
                //添加
                if(ENTER_STATIC==0){
                    if(!mesg.isEmpty()){
                        Date date = new Date();
                        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
                        String dateString = sdf.format(date);

                        //向数据库添加信息

                        ContentValues cv = new ContentValues();
                        cv.put("content",mesg);
                        cv.put("date",dateString);
                        db.insert("note",null,cv);
                    }else {
                        Toast.makeText(getBaseContext(),"请输入内容",Toast.LENGTH_LONG).show();
                    }
                }else {
                    // 查看并修改一个已有的日志
                    ContentValues cv = new ContentValues();
                    cv.put("content",mesg);
                    db.update("note",cv,"content=?",new String[]{last_content});

                }
                finish();
                break;

            case R.id.bt_cancel:
                finish();
                break;
            default:
                break;
        }
    }
}

SQlite有个问题，就是主键不能够自动排序。比如说主键id为1 2 3 4，共4条记录。现在删除2 3，还剩下1 4记录，当再次插入时，id会变成5，而不是2.假设在初始4条记录的基础上，把这4条记录全都删掉，再次插入时，得到的id是5.

所以，需要从listview的每个item中获取内容，然后到数据库中通过内容搜索该记录，最后对其进行操作。