轉載地址:http://blog.csdn.net/heng615975867/article/details/9194219
Android中的Looper類,是用來封裝消息循環和消息隊列的一個類,用於在android線程中進行消息處理。handler其實可以看做是一個工具類,用來向消息隊列中插入消息的。
(1) Looper類用來爲一個線程開啓一個消息循環。 默認情況下android中新誕生的線程是沒有開啓消息循環的。(主線程除外,主線程系統會自動爲其創建Looper對象,開啓消息循環。) Looper對象通過MessageQueue來存放消息和事件。一個線程只能有一個Looper,對應一個MessageQueue。
(2) 通常是通過Handler對象來與Looper進行交互的。Handler可看做是Looper的一個接口,用來向指定的Looper發送消息及定義處理方法。 默認情況下Handler會與其被定義時所在線程的Looper綁定,比如,Handler在主線程中定義,那麼它是與主線程的Looper綁定。 mainHandler = new Handler() 等價於new Handler(Looper.myLooper()). Looper.myLooper():獲取當前進程的looper對象,類似的 Looper.getMainLooper() 用於獲取主線程的Looper對象。
(3) 在非主線程中直接new Handler() 會報如下的錯誤: E/AndroidRuntime( 6173): Uncaught handler: thread Thread-8 exiting due to uncaught exception E/AndroidRuntime( 6173): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 原因是非主線程中默認沒有創建Looper對象,需要先調用Looper.prepare()啓用Looper。
(4) Looper.loop(); 讓Looper開始工作,從消息隊列裏取消息,處理消息。
(5) 基於以上知識,可實現主線程給子線程(非主線程)發送消息。
把下面例子中的mHandler聲明成類成員,在主線程通過mHandler發送消息即可。 Android官方文檔中Looper的介紹: Class used to run a message loop for a thread. Threads by default do not have a message loop associated with them; to create one, call prepare() in the thread that is to run the loop, and then loop() to have it process messages until the loop is stopped.
Most interaction with a message loop is through the Handler class.
This is a typical example of the implementation of a Looper thread, using the separation of prepare() and loop() to create an initial Handler to communicate with the Looper.
- class LooperThread extends Thread
- {
- public Handler mHandler;
- public void run()
- {
- Looper.prepare();
- mHandler = new Handler()
- {
- public void handleMessage(Message msg)
- {
- // process incoming messages here
- }
- };
- Looper.loop();
- }
class LooperThread extends Thread
{
public Handler mHandler;
public void run()
{
Looper.prepare();
mHandler = new Handler()
{
public void handleMessage(Message msg)
{
// process incoming messages here
}
};
Looper.loop();
}
android HandlerThread使用小例
之前研究過handler 和 looper 消息隊列,不過android裏的handler不是另外開啓線程來執行的,還是在主UI線程中,如果想另啓線程的話需要用到HandlerThread來實現。在使用HandlerThread的時候需要實現CallBack接口以重寫handlerMessage方法,在handlerMessage方法中來處理自己的邏輯。下來給出一個小例子程序。
layout文件很簡單,就一個按鈕來啓動HanlderTread線程
- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent"
- android:orientation="vertical" >
- <TextView
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:text="@string/hello" />
- <Button
- android:id="@+id/handlerThreadBtn"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:text="startHandlerThread" />
- </LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
<Button
android:id="@+id/handlerThreadBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="startHandlerThread" />
</LinearLayout>
Activity代碼如下:
- package com.tayue;
- import android.app.Activity;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.Handler.Callback;
- import android.os.HandlerThread;
- import android.os.Message;
- import android.view.View;
- import android.view.View.OnClickListener;
- import android.widget.Button;
- /**
- *
- * @author xionglei
- *
- */
- public class TestHandlerActivity extends Activity implements OnClickListener{
- public Button handlerThreadBTN;
- MyHandlerThread handlerThread;
- Handler handler;
- /** Called when the activity is first created. */
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- //打印UI線程的名稱
- System.out.println("onCreate CurrentThread = " + Thread.currentThread().getName());
- setContentView(R.layout.main);
- handlerThreadBTN = (Button) findViewById(R.id.handlerThreadBtn);
- handlerThreadBTN.setOnClickListener(this);
- handlerThread = new MyHandlerThread("myHanler");
- handlerThread.start();
- //注意: 這裏必須用到handler的這個構造器,因爲需要把callback傳進去,從而使自己的HandlerThread的handlerMessage來替換掉Handler原生的handlerThread
- handler = new Handler(handlerThread.getLooper(), handlerThread);
- }
- @Override
- public void onClick(View v) {
- //點擊按鈕後來開啓線程
- handler.sendEmptyMessage(1);
- }
- private class MyHandlerThread extends HandlerThread implements Callback {
- public MyHandlerThread(String name) {
- super(name);
- }
- @Override
- public boolean handleMessage(Message msg) {
- //打印線程的名稱
- System.out.println(" handleMessage CurrentThread = " + Thread.currentThread().getName());
- return true;
- }
- }
- }
package com.tayue;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Handler.Callback;
import android.os.HandlerThread;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
/**
*
* @author xionglei
*
*/
public class TestHandlerActivity extends Activity implements OnClickListener{
public Button handlerThreadBTN;
MyHandlerThread handlerThread;
Handler handler;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//打印UI線程的名稱
System.out.println("onCreate CurrentThread = " + Thread.currentThread().getName());
setContentView(R.layout.main);
handlerThreadBTN = (Button) findViewById(R.id.handlerThreadBtn);
handlerThreadBTN.setOnClickListener(this);
handlerThread = new MyHandlerThread("myHanler");
handlerThread.start();
//注意: 這裏必須用到handler的這個構造器,因爲需要把callback傳進去,從而使自己的HandlerThread的handlerMessage來替換掉Handler原生的handlerThread
handler = new Handler(handlerThread.getLooper(), handlerThread);
}
@Override
public void onClick(View v) {
//點擊按鈕後來開啓線程
handler.sendEmptyMessage(1);
}
private class MyHandlerThread extends HandlerThread implements Callback {
public MyHandlerThread(String name) {
super(name);
}
@Override
public boolean handleMessage(Message msg) {
//打印線程的名稱
System.out.println(" handleMessage CurrentThread = " + Thread.currentThread().getName());
return true;
}
}
}
點擊按鈕,打印的日誌如下(這裏點擊了3次) 07-06 09:32:48.776: I/System.out(780): onCreate CurrentThread = main 07-06 09:32:55.076: I/System.out(780): handleMessage CurrentThread = myHanler 07-06 09:32:58.669: I/System.out(780): handleMessage CurrentThread = myHanler 07-06 09:33:03.476: I/System.out(780): handleMessage CurrentThread = myHanler
HandlerThread就這麼簡單。
當然 android自己也有異步線程的handler,就是AsyncTask,這個類就是封裝了HandlerThread 和handler來實現異步多線程的操作的。
同樣可以這樣使用:
- private boolean iscancel = false; //用戶手動取消登錄的標誌位
- handlerThread = new HandlerThread("myHandlerThread");
- handlerThread.start();
- handler = new MyHandler(handlerThread.getLooper());
- // 將要執行的線程對象添加到線程隊列中
- handler.post(new Runnable() {
- @Override
- public void run() {
- Message message = handler.obtainMessage();
- UserBean user = Bbs.getInstance().Login(username, password);//耗時任務
- Bundle b = new Bundle();
- b.putSerializable("user", user);
- message.setData(b);
- message.sendToTarget(); //或使用 handler.sendMessage(message);
- }
- });
- class MyHandler extends Handler {
- public MyHandler(Looper looper) {
- super(looper);
- }
- @Override
- public void handleMessage(Message msg) {
- if(iscancel == false){
- // 操作UI線程的代碼
- Bundle b = msg.getData();
- UserBean user = (UserBean)b.get("user");
- ......
- }
- }
- }