public final void registerContentObserver (Uri uri, boolean notifyForDescendents, ContentObserver observer)

注冊(cè)一個(gè)觀察者實(shí)例，當(dāng)指定的Uri發(fā)生改變時(shí)，這個(gè)實(shí)例會(huì)回調(diào)實(shí)例對(duì)象做相應(yīng)處理。

參數(shù)：uri:需要觀察的Uri

          notifyForDescendents：如果為true表示以這個(gè)Uri為開(kāi)頭的所有Uri都會(huì)被匹配到，

    如果為false表示精確匹配，即只會(huì)匹配這個(gè)給定的Uri。

  舉個(gè)例子，假如有這么幾個(gè)Uri：

①content://com.example.studentProvider/student

②content://com.example.studentProvider/student/#

③content://com.example.studentProvider/student/10

④content://com.example.studentProvider/student/teacher

假如觀察的Uri為content://com.example.studentProvider/student，當(dāng)notifyForDescendents為true時(shí)則以這個(gè)Uri開(kāi)頭的Uri的數(shù)據(jù)變化時(shí)都會(huì)被捕捉到，在這里也就是①②③④的Uri的數(shù)據(jù)的變化都能被捕捉到，當(dāng)notifyForDescendents為false時(shí)則只有①中Uri變化時(shí)才能被捕捉到。

       看到registerContentObserver 這個(gè)方法，根據(jù)語(yǔ)言基礎(chǔ)我想大家能夠想到ContentResolver中的另一個(gè)方法

public final voidunregisterContentObserver(ContentObserverobserver)它的作用就是取消對(duì)注冊(cè)的那個(gè)Uri的觀察，這里傳進(jìn)去的就是在registerContentObserver中傳遞進(jìn)去的ContentObserver對(duì)象。到這關(guān)于注冊(cè)和解除注冊(cè)的ContentObserver可能大家都比較清楚了，那么問(wèn)題來(lái)了，怎么去寫(xiě)一個(gè)ContentObserver呢？其實(shí)它的實(shí)現(xiàn)很簡(jiǎn)單，直接創(chuàng)建一個(gè)類(lèi)繼承ContentObserver需要注意的是這里必須要實(shí)現(xiàn)它的構(gòu)造方法

public ContentObserver(Handlerhandler)

這里傳進(jìn)去的是一個(gè)Handler對(duì)象，這個(gè)Handler對(duì)象的作用一般要依賴(lài)于ContentObserver的另一個(gè)方法即

public void onChange(boolean selfChange)

這個(gè)方法的作用就是當(dāng)指定的Uri的數(shù)據(jù)發(fā)生變化時(shí)會(huì)回調(diào)該方法，此時(shí)可以借助構(gòu)造方法中的Handler對(duì)象將這個(gè)變化的消息發(fā)送給主線程，當(dāng)主線程接收到這個(gè)消息之后就可以按照我們的需求來(lái)完成相應(yīng)的操作，比如上面提到的類(lèi)似于Adapter的notifyDataSetChanged()的作用，下面的案例也是完成了這個(gè)功能，準(zhǔn)備工作完成之后來(lái)看一個(gè)案例，相信這個(gè)案例會(huì)讓你對(duì)以上知識(shí)了解的更加深入。

<provider 
      android:name="com.example.contentproviderpractice.PeopleContentProvider"
      android:authorities="com.example.student"
      android:exported="true" >
</provider>

package com.example.otherapplication;
import java.util.ArrayList;
import com.example.otherapplication.adapter.MyAdapter;
import com.example.otherapplication.bean.Student;
import com.example.otherapplication.observer.PersonOberserver;
import android.net.Uri;
import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ListView;
public class MainActivity extends Activity implements OnClickListener {
	private ContentResolver contentResolver;
	private ListView lvShowInfo;
	private MyAdapter adapter;
	private Button btnInit;
	private Button btnInsert;
	private Button btnDelete;
	private Button btnUpdate;
	private Button btnQuery;
	private Cursor cursor;
	private static final String AUTHORITY = "com.example.studentProvider";  
    private static final Uri STUDENT_ALL_URI = Uri.parse("content://" + AUTHORITY + "/student");
	protected static final String TAG = "MainActivity"; 
    private Handler handler=new Handler(){
    	public void handleMessage(android.os.Message msg) {
    		//在此我們可以針對(duì)數(shù)據(jù)改變后做一些操作，比方說(shuō)Adapter.notifyDataSetChanged()等，根據(jù)業(yè)務(wù)需求來(lái)定。。
    		cursor = contentResolver.query(STUDENT_ALL_URI, null, null, null,null);
    	    adapter.changeCursor(cursor);
    	};
    };
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		lvShowInfo=(ListView) findViewById(R.id.lv_show_info);
		initData();
	}
	private void initData() {
		btnInit=(Button) findViewById(R.id.btn_init);
		btnInsert=(Button) findViewById(R.id.btn_insert);
		btnDelete=(Button) findViewById(R.id.btn_delete);
		btnUpdate=(Button) findViewById(R.id.btn_update);
		btnQuery=(Button) findViewById(R.id.btn_query);
		btnInit.setOnClickListener(this);
		btnInsert.setOnClickListener(this);
		btnDelete.setOnClickListener(this);
		btnUpdate.setOnClickListener(this);
		btnQuery.setOnClickListener(this);
		contentResolver = getContentResolver();
		//注冊(cè)內(nèi)容觀察者
		contentResolver.registerContentObserver(STUDENT_ALL_URI,true,new PersonOberserver(handler));
		adapter=new MyAdapter(MainActivity.this,cursor);
		lvShowInfo.setAdapter(adapter);
	}
	@Override
	public void onClick(View v) {
		switch (v.getId()) {
		//初始化
		case R.id.btn_init:
			ArrayList<Student> students = new ArrayList<Student>();  
	        Student student1 = new Student("蒼老師",25,"一個(gè)會(huì)教學(xué)的好老師");  
	        Student student2 = new Student("柳巖",26,"大方");  
	        Student student3 = new Student("楊冪",27,"漂亮");  
	        Student student4 = new Student("張馨予",28,"不知道怎么評(píng)價(jià)");  
	        Student student5 = new Student("范冰冰",29,"。。。");
	        students.add(student1);  
	        students.add(student2);  
	        students.add(student3);  
	        students.add(student4); 
	        students.add(student5); 
	        for (Student Student : students) {  
	            ContentValues values = new ContentValues();  
	            values.put("name", Student.getName());  
	            values.put("age", Student.getAge());  
	            values.put("introduce", Student.getIntroduce());  
	            contentResolver.insert(STUDENT_ALL_URI, values);  
	        }
			break;
		//增
		case R.id.btn_insert:
			Student student = new Student("小明", 26, "帥氣男人");  
			//實(shí)例化一個(gè)ContentValues對(duì)象
	        ContentValues insertContentValues = new ContentValues();  
	        insertContentValues.put("name",student.getName());  
	        insertContentValues.put("age",student.getAge());  
	        insertContentValues.put("introduce",student.getIntroduce());  
			//這里的uri和ContentValues對(duì)象經(jīng)過(guò)一系列處理之后會(huì)傳到ContentProvider中的insert方法中，
			//在我們自定義的ContentProvider中進(jìn)行匹配操作
			contentResolver.insert(STUDENT_ALL_URI,insertContentValues);
			break;
		//刪
		case R.id.btn_delete:
	        //刪除所有條目
	        contentResolver.delete(STUDENT_ALL_URI, null, null); 
			//刪除_id為1的記錄  
	        Uri delUri = ContentUris.withAppendedId(STUDENT_ALL_URI,1);  
	        contentResolver.delete(delUri, null, null);
			break;
		//改
		case R.id.btn_update:
			ContentValues contentValues = new ContentValues();
			contentValues.put("introduce","性感");
			//更新數(shù)據(jù)，將age=26的條目的introduce更新為"性感"，原來(lái)age=26的introduce為"大方".
			//生成的Uri為：content://com.example.studentProvider/student/26
			Uri updateUri = ContentUris.withAppendedId(STUDENT_ALL_URI,26);
			contentResolver.update(updateUri,contentValues, null, null);
			break;
		//查
		case R.id.btn_query:
		    //通過(guò)ContentResolver獲得一個(gè)調(diào)用ContentProvider對(duì)象
			Cursor cursor = contentResolver.query(STUDENT_ALL_URI, null, null, null,null);
			//CursorAdapter的用法，參考此博客：http://blog.csdn.net/dmk877/article/details/44983491
			adapter=new MyAdapter(MainActivity.this,cursor);
			lvShowInfo.setAdapter(adapter);
			cursor = contentResolver.query(STUDENT_ALL_URI, null, null, null,null);
			adapter.changeCursor(cursor);
			break;
		}
	}
}

package com.example.otherapplication.observer;
import android.database.ContentObserver;
import android.os.Handler;
import android.os.Message;
public class PersonOberserver extends ContentObserver {
	private Handler handler;
	public PersonOberserver(Handler handler) {
		super(handler);
		this.handler=handler;
	}
	@Override
	public void onChange(boolean selfChange) {
		super.onChange(selfChange);
        //向handler發(fā)送消息,更新查詢(xún)記錄  
        Message msg = new Message();  
        handler.sendMessage(msg);
	}
}