关于Handler处理UI线程的更新及Handler译文

Android UI操作并不是线程安全的并且这些操作必须在UI线程中执行。Android利用Handler来实现UI线程的更新的。

Handler是Android中的消息发送器，其在哪个Activity中创建就属于且紧紧属于该Activity。还可以说其在哪个线程中new的，就是那个线程的Handler。

Handler的定义: 主要接受子线程发送的数据, 并用此数据配合主线程更新UI. 

解释: 当应用程序启动时，Android首先会开启一个主线程 (也就是UI线程) , 主线程为管理界面中的UI控件，进行事件分发, 比如说, 你要是点击一个 Button ,Android会分发事件到Button上，来响应你的操作。  如果此时需要一个耗时的操作，例如: 联网读取数据，或者读取本地较大的一个文件的时候，你不能把这些操作放在主线程中，，如果你放在主线程中的话，界面会出现假死现象,如果5秒钟还没有完成的话，会收到Android系统的一个错误提示 "强制关闭".这个时候我们需要把这些耗时的操作，放在一个子线程中,因为子线程涉及到UI更新，Android主线程是线程不安全的，也就是说，更新UI只能在主线程中更新，子线程中操作是危险的. 这个时候，Handler就出现了.来解决这个复杂的问题,由于Handler运行在主线程中(UI线程中),  它与子线程可以通过Message对象来传递数据, 这个时候，Handler就承担着接受子线程传过来的(子线程用sedMessage()方法传弟)Message对象，(里面包含数据),把这些消息放入主线程队列中，配合主线程进行更新UI。

以上解释原地址：http://txlong-onz.iteye.com/blog/934957

 

handler API 译文

A Handler allows you to send andprocess Message andRunnable objects associated with a thread's MessageQueue.Each Handler instance is associated with a single thread and that thread'smessage queue. When you create a new Handler, it is bound to the thread /message queue of the thread that is creating it -- from that point on, it willdeliver messages and runnables to that message queue and execute them as theycome out of the message queue.

一个Handler允许你去发送和处理一个Message或者是和与一个线程的MessageQueue关联的Runnable对象。每一个Handler的实例都与一个单线程Thread以及该线程的消息队列MessageQueue关联。当你创建一个新的Handler时，它约束于这个创建它的线程或者线程的队列-从这一点看，他会将Message和Runnable发送给消息队列，并在它们从队列中出来时，处理它们。

 

There are two main uses for a Handler: (1)to schedule messages and runnables to be executed as some point in the future;and (2) to enqueue an action to be performed on a different thread than yourown.

Handler有两种用法：（1）安排Message和Runnable的执行顺序（2）将某一个操作放在另一个线程中执行。

 

Scheduling messages is accomplished withthe post(Runnable), postAtTime(Runnable,long), postDelayed(Runnable,long), sendEmptyMessage(int),sendMessage(Message), sendMessageAtTime(Message,long), and sendMessageDelayed(Message,long) methods. The post versions allow you to enqueueRunnable objects to be called by the message queue when they are received;the sendMessage versions allow you to enqueue a Message objectcontaining a bundle of data that will be processed by the Handler's handleMessage(Message) method(requiring that you implement a subclass of Handler).

post(Runnable), postAtTime(Runnable,long), postDelayed(Runnable,long), sendEmptyMessage(int),sendMessage(Message), sendMessageAtTime(Message,long),sendMessageDelayed(Message,long)方法能够完成消息的处理。Post的函数允许你安排由消息队列调用的Runnable对象。Send的函数允许你安排Message对象，该Message对象包含有一个Bundle数据，该Message传递给是一个实现了Handler类的 handleMessage(Message)方法。

 

When posting or sending to a Handler, youcan either allow the item to be processed as soon as the message queue is readyto do so, or specify a delay before it gets processed or absolute time for itto be processed. The latter two allow you to implement timeouts, ticks, andother timing-based behavior.

当你使用posting或者sending的传递消息给一个Handler时，你可以立刻处理这个它，或者指定一个延迟时间或者准确的时间处理。后两者需要你实现timeouts, ticks, and other timing-based behavior.

 

When a process is created for yourapplication, its main thread is dedicated to running a message queue that takescare of managing the top-level application objects (activities, broadcastreceivers, etc) and any windows they create. You can create your own threads,and communicate back with the main application thread through a Handler. Thisis done by calling the same post or sendMessage methods asbefore, but from your new thread. The given Runnable or Message will then bescheduled in the Handler's message queue and processed when appropriate.

当你的应用程序的一个处理被创建，它的主线程会放置到一个管理顶级应用程序对象的消息队列中（包括activities, broadcast receivers, etc）。你可以创建你自己的线程，通过Handler和主线程通信。方法是通过在你的线程中调用post或者sendMessage方法。Runnable和Message会被安排到Handler的消息队列中并在合适的时候处理。

 

While the constructor of Message is public,the best way to get one of these is to call Message.obtain() orone of the Handler.obtainMessage() methods,which will pull them from a pool of recycled objects.

虽然Message的构造方法是public的，但是获得Message的最好方法是通过Message.obtain() 或者Handler.obtainMessage() 中的一种，它们会从循环池中得到Message.

代码：

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    ><Button android:id="@+id/MyButton"android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:text="启动"/></LinearLayout>

dialogview.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout  xmlns:android="http://schemas.android.com/apk/res/android"  android:orientation="vertical"  android:layout_width="fill_parent"  android:layout_height="wrap_content">    <TextView     android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:text="handler接受消息，启动本对话框"/></LinearLayout>

Acitvity

package com.zeph.android.myhandler;import android.app.Activity;import android.app.AlertDialog;import android.app.AlertDialog.Builder;import android.app.ProgressDialog;import android.content.DialogInterface;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class AndroidHandlerActivity extends Activity {private Button mButton;private ProgressDialog mProgressDialog;private MyHandler myHandler;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);mButton = (Button) findViewById(R.id.MyButton);myHandler = new MyHandler();mButton.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View arg0) {mProgressDialog = new ProgressDialog(AndroidHandlerActivity.this);mProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);mProgressDialog.setTitle("请等待");mProgressDialog.setMessage("线程等待5秒，调用dismiss()函数和Handler发送msg");mProgressDialog.setIndeterminate(false);mProgressDialog.setCancelable(false);mProgressDialog.show();new Thread(new MyThread(mProgressDialog, myHandler)).start();}});}public void ShowDialog() {Builder builder = new AlertDialog.Builder(AndroidHandlerActivity.this);builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface arg0, int arg1) {}});AlertDialog mAlertDialog = builder.create();mAlertDialog.setTitle("进程结束对话框");LayoutInflater factory = getLayoutInflater();View loginDialogView = factory.inflate(R.layout.dialogview, null);mAlertDialog.setView(loginDialogView);mAlertDialog.show();}public class MyHandler extends Handler {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);switch (msg.arg1) {case 0:ShowDialog();break;default:break;}}}public class MyThread implements Runnable {private MyHandler myHandler;private ProgressDialog mProgressDialog;public MyThread(ProgressDialog mProgressDialog, MyHandler myHandler) {this.myHandler = myHandler;this.mProgressDialog = mProgressDialog;}@Overridepublic void run() {try {Thread.sleep(5000);} catch (InterruptedException e) {e.printStackTrace();}mProgressDialog.dismiss();Message msg = new Message();msg.arg1 = 0;myHandler.sendMessage(msg);}}}