Android 自定义ContentProvider

╰半夏微凉° 2021-07-04 16:06 457阅读 0赞

Android允许我们定义自己的的ContentProvider对象来共享数据，练练手，简单来实现一下。

要使用ContentProvider来操作数据，必须要有保存数据的场所。可以使用文件或SQLite数据库的方式来保存数据，通常使用SQLite数据库。

**1，创建一个数据库帮助类，归根结底都是它在操作数据库。代码如下：**

package com.njue;
    
    import android.content.Context;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteDatabase.CursorFactory;
    import android.database.sqlite.SQLiteOpenHelper;
    
    public class DBManager extends SQLiteOpenHelper {
    public static final String myProvider_table_name="myProvider_table_name";
    String sql="create table myProvider_table_name(id integer,name text)";
    	public DBManager(Context context) {
    		super(context, "myPrivoder.db", null, 1);
    		// TODO Auto-generated constructor stub
    	}
    
    	@Override
    	public void onCreate(SQLiteDatabase arg0) {
    		// TODO Auto-generated method stub
          arg0.execSQL(sql);
    	}
    
    	@Override
    	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    		// TODO Auto-generated method stub
    
    	}
    
    }

**2，创建一个myProvider类，该类继承ContentProvider，实现其抽象方法来操作数据库，该类引用DBManager类来获得数据库实例。**

package com.njue;
    
    import android.content.ContentProvider;
    import android.content.ContentValues;
    import android.database.Cursor;
    import android.database.sqlite.SQLiteDatabase;
    import android.net.Uri;
    
    public class myProvider extends ContentProvider {
        DBManager dbHelper;
    	@Override
    	public int delete(Uri arg0, String arg1, String[] arg2) {
    		// TODO Auto-generated method stub
    		SQLiteDatabase db=dbHelper.getWritableDatabase();
    		int id=db.delete(DBManager.myProvider_table_name, arg1, arg2);
    		if(id!=0)return id;
    		return 0;
    	}
    
    	@Override
    	public String getType(Uri uri) {
    		// TODO Auto-generated method stub
    		return null;
    	}
    
    	@Override
    	public Uri insert(Uri uri, ContentValues values) {
    		// TODO Auto-generated method stub
    		SQLiteDatabase db=dbHelper.getWritableDatabase();
    		db.insert(DBManager.myProvider_table_name, "id", values);
    		return null;
    	}
    
    	@Override
    	public boolean onCreate() {
    		// TODO Auto-generated method stub
    		dbHelper=new DBManager(getContext());
    		return true;
    	}
    
    	@Override
    	public Cursor query(Uri uri, String[] projection, String selection,
    			String[] selectionArgs, String sortOrder) {
    		// TODO Auto-generated method stub
    		SQLiteDatabase db=dbHelper.getWritableDatabase();
    		Cursor c=db.query(DBManager.myProvider_table_name,projection, selection, selectionArgs, null, null, sortOrder);
    		return c;
    	}
    
    	@Override
    	public int update(Uri uri, ContentValues values, String selection,
    			String[] selectionArgs) {
    		// TODO Auto-generated method stub
    		SQLiteDatabase db=dbHelper.getWritableDatabase();
    		int id=db.update(DBManager.myProvider_table_name, values, selection, selectionArgs);
    		if(id!=0)return id;
    		return 0;
    	}
    
    }

**3，ContextProvider必须声明才能使用，因此，需要在AndroidManifest.xml配置文件中声明。声明很简单，需要类名称和授权名称两个属性。**

到这里，我们自定义的ContentProvider就完成了。我们可以在Eclipse中的File Explorer 窗口中看到自定义的ContentProvider

![1350743438_1477.JPG][]

**4，简单测试**

package com.njue;
    
    import android.app.Activity;
    import android.content.ContentResolver;
    import android.content.ContentValues;
    import android.database.Cursor;
    import android.net.Uri;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.View;
    import android.widget.Button;
    import android.widget.EditText;
    import android.widget.TextView;
    
    public class Content_providerActivity extends Activity {
        /** Called when the activity is first created. */
    	 Uri uri;
    	 String AUTHORITY="content://com.njue.myProvider/myProvider_table_name";
    	 ContentResolver cr;
    	 EditText input;
    	 Button insert;
    	 TextView show;
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
           setContentView(R.layout.main);
           input=(EditText)findViewById(R.id.input);
           insert=(Button)findViewById(R.id.insert);
           show=(TextView)findViewById(R.id.show);
            uri=uri.parse(AUTHORITY);
            cr=this.getContentResolver();
            insert.setOnClickListener(new Button.OnClickListener(){
    
    			@Override
    			public void onClick(View v) {
    				// TODO Auto-generated method stub
    				 ContentValues values=new ContentValues();
    			        values.put("name", input.getText().toString());
    			        cr.insert(uri, values);
    			        Cursor c=cr.query(uri, null, null, null, null);
    			        show.setText("");
    			        c.moveToFirst();
    			        while(c.moveToNext()){
    			         show.append(c.getString(1)+"\r\n");
    			        }
    			        input.setText("");
    			}});
           
        }
    }

[1350743438_1477.JPG]: https://img-my.csdn.net/uploads/201210/20/1350743438_1477.JPG