android15

【监听ContentProvider中数据的变化】

如果ContentProvider的访问者需要知道ContentProvider中的数据发生变化，可以在ContentProvider 发生数据变化时调用getContentResolver().notifyChange(uri, null)来通知注册在此URI上的访问者，例子如下：
public class PersonContentProvider extends ContentProvider {
public Uri insert(Uri uri, ContentValues values) {
 db.insert("person", "personid", values);
 getContext().getContentResolver().notifyChange(uri, null);
}
}
如果ContentProvider的访问者需要得到数据变化通知，必须使用ContentObserver对数据（数据采用uri描述）进行监听，当监听到数据变化通知时，系统就会调用ContentObserver的onChange()方法：
getContentResolver().registerContentObserver(Uri.parse("content://cn.itcast.providers.personprovider/person"),
          true,//true表示只要发出通知的Uri以方法第一个参数开头都能被监听到，否侧监听uri必须与发出通知的uri完全匹配才能被监听到
                                           new PersonObserver(new Handler()));
public class PersonObserver extends ContentObserver{
 public PersonObserver(Handler handler) {
  super(handler);
  }
 public void onChange(boolean selfChange) {
     //此处可以进行相应的业务处理
 }
}

package cn.itcast.app;

import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    
    public void insert(View v){
        Uri uri = Uri.parse("content://cn.itcast.providers.personprovider/person");
        ContentResolver resolver = this.getContentResolver();
        ContentValues values = new ContentValues();
        values.put("name", "A-App");
        values.put("phone", "18607687688");
        values.put("amount", "700000");
        resolver.insert(uri, values);
    }
}

package cn.itcast.other;

import android.app.Activity;
import android.database.ContentObserver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Uri uri = Uri.parse("content://cn.itcast.providers.personprovider/person");
        this.getContentResolver().registerContentObserver(uri, true, new PersonContentObserver(new Handler()));
    }
    
    private class PersonContentObserver extends ContentObserver{

        public PersonContentObserver(Handler handler) {
            super(handler);
        }

        @Override
        public void onChange(boolean selfChange) {
            // select * from person order by personid desc limit 1
            Uri uri = Uri.parse("content://cn.itcast.providers.personprovider/person");
            Cursor cursor = getContentResolver().query(uri, null, null, null, "personid desc limit 1");
            if(cursor.moveToFirst()){
                String name = cursor.getString(cursor.getColumnIndex("name"));
                Log.i("MainActivity", name);
            }
        }
        
    }
}