ContentProvider将程序中的数据暴露给其他程序访问

package com.example.accountsoft.dao;

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 {
    private DBOpenHelper helper;
    private SQLiteDatabase db;

    public MyProvider() {
        super();
    }

    @Override
    public boolean onCreate() {
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        helper = new DBOpenHelper(getContext());
        db = helper.getWritableDatabase();
        Cursor cursor = db.query("tb_inaccount", null, null, null, null, null, null, null);
        return cursor;
    }

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

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        return 0;
    }
}

        <provider 
            android:name="com.example.accountsoft.dao.MyProvider"
            android:exported="true"
            android:authorities="com.example.accountsoft.dao.MyProvider">
            <!-- exported选项表示是否能够被其他应用调用    -->
        </provider>

package com.example.accountreader;

import android.app.Activity;
import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
    private Button button;
    private TextView content;

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

        content = (TextView)findViewById(R.id.textView1);

        button = (Button)findViewById(R.id.button1);
        button.setOnClickListener(new OnClickListener(){
            @Override
            public void onClick(View v) {
                ContentResolver resolver = getContentResolver();

                Uri uri = Uri.parse("content://com.example.accountsoft.dao.MyProvider/tb_inaccount");
                //content+authorities+table_name
                Cursor cursor = resolver.query(uri, null, null, null, null);

                StringBuilder stringBuilder = new StringBuilder();
                while (cursor != null && cursor.moveToNext()) {
                    int id = cursor.getInt(cursor.getColumnIndex("_id"));
                    double money = cursor.getDouble(cursor.getColumnIndex("money"));
                    stringBuilder.append(id+"+"+money+"\n");
                }
                content.setText(stringBuilder.toString());
            }
        });
    }
}