Android之ContentProvider

ContentProvider，实现跨程序数据共享，像是通讯录之类的都有使用。以下为代码。

DbOpenHelper.java代码:

package com.minardwu.learnprovider;

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

/**
 * Created by MinardWu on 2016/10/4.
 */
public class DbOpenHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "myprovide.db";
    private static final int DB_VERSION = 1;
    public static final String TABLE_USER_NAME = "user";
    public static final String TABLE_BOOK_NAME = "book";
    private String CREATE_TABLE_USER = "create table if not exists "+TABLE_USER_NAME+"(_id INTEGER　PRIMARY KRY,name TEXT,sex INT)";
    private String CREATE_TABLE_BOOK = "create table if not exists "+TABLE_BOOK_NAME+"(_id INTEGER　PRIMARY KRY,name TEXT)";

    public DbOpenHelper(Context context) {
        super(context,DB_NAME, null, DB_VERSION);
    }

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

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

    }
}
MyProvider代码:

package com.minardwu.learnprovider;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.annotation.Nullable;

import java.net.URI;

/**
 * Created by MinardWu on 2016/10/4.
 */
public class MyProvider extends ContentProvider{

    public static final String AUTHORITIES = "com.minardwu.learnprovider.MyProvider";
    public static final Uri USER_URI = Uri.parse("content://"+AUTHORITIES+"/user");
    public static final Uri BOOK_URI = Uri.parse("content://"+AUTHORITIES+"/book");
    public static final int USER_URI_CODE = 0;
    public static final int BOOK_URI_CODE = 1;
    private static final UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
    static {
        matcher.addURI(AUTHORITIES,"user",USER_URI_CODE);
        matcher.addURI(AUTHORITIES,"book",BOOK_URI_CODE);
    }
    private SQLiteDatabase sqLiteDatabase;

    @Override
    public boolean onCreate() {
        sqLiteDatabase = new DbOpenHelper(getContext()).getWritableDatabase();
        sqLiteDatabase.execSQL("delete from "+DbOpenHelper.TABLE_USER_NAME);
        sqLiteDatabase.execSQL("delete from "+DbOpenHelper.TABLE_BOOK_NAME);
        sqLiteDatabase.execSQL("insert into user values(1,'wu','1');");
        sqLiteDatabase.execSQL("insert into book values(1,'Android');");
        return true;
    }

    private String getTableName(Uri uri){
        String tableName = null;
        switch (matcher.match(uri)){
            case USER_URI_CODE:
                tableName = DbOpenHelper.TABLE_USER_NAME;
                break;
            case BOOK_URI_CODE:
                tableName = DbOpenHelper.TABLE_BOOK_NAME;
                break;
            default:
                break;
        }
        return tableName;
    }

    //Provider的增删改查函数里面执行的是SQLite数据库的增删改查函数,sqLiteDatabase.query/insert/update/delete.
    @Nullable
    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
        //先确定是哪个表，所有操作都有以下两个步骤
        String tableName = getTableName(uri);
        if(tableName==null) throw new IllegalArgumentException("uri为："+uri+"，找不到对应的表。");
        return sqLiteDatabase.query(tableName,projection,selection,selectionArgs,null,null,sortOrder,null);
    }

    //update、insert、delete会引起数据源的改变所以需要notifyChange()函数来通知外界数据已经发生变化
    @Nullable
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        String tableName = getTableName(uri);
        if(tableName==null) throw new IllegalArgumentException("uri为："+uri+"，找不到对应的表。");
        sqLiteDatabase.insert(tableName,null,values);
        getContext().getContentResolver().notifyChange(uri,null);
        return uri;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        String tableName = getTableName(uri);
        if(tableName==null) throw new IllegalArgumentException("uri为："+uri+"，找不到对应的表。");
        int count = sqLiteDatabase.delete(tableName,selection,selectionArgs);
        if(count>0) getContext().getContentResolver().notifyChange(uri,null);//count>0表明有数据被删除
        return count;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        String tableName = getTableName(uri);
        if(tableName==null) throw new IllegalArgumentException("uri为："+uri+"，找不到对应的表。");
        int count = sqLiteDatabase.update(tableName,values,selection,selectionArgs);
        if(count>0) getContext().getContentResolver().notifyChange(uri,null);//count>0表明有数据被更新
        return count;
    }

    @Nullable
    @Override
    public String getType(Uri uri) {
        return null;
    }

}

MainActivity代码:

package com.minardwu.learnprovider;

import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ContentValues values = new ContentValues();
        values.put("_id","2");
        values.put("name","zhang");
        //调用ContentProvider的insert函数，该函数有调用数据库的insert函数
        getContentResolver().insert(MyProvider.USER_URI,values);
        Cursor cursor = getContentResolver().query(MyProvider.USER_URI,new String[]{"_id","name"},null,null,null);
        while (cursor.moveToNext()){
            System.out.println(cursor.getInt(0)+cursor.getString(1));
        }
        cursor.close();
    }
}