有主線程發送message給子線程，主線程發送message

有主線程發送message給子線程，主線程發送message

 

　　通常我們在處理耗時任務時候都會通過建立線程來處理，當任務處理完後通過Handler將結果發送回主線程。比如下面樣本：

 1 package com.example.testlistener; 2  3 import java.util.Timer; 4 import java.util.TimerTask; 5  6 import android.app.Activity; 7 import android.content.res.Configuration; 8 import android.os.Bundle; 9 import android.os.Handler;10 import android.os.Message;11 import android.view.View;12 import android.view.View.OnClickListener;13 import android.view.View.OnLongClickListener;14 import android.widget.Button;15 import android.widget.EditText;16 import android.widget.Toast;17 18 public class MainActivity extends Activity {19     EditText txt;20     final Handler hander = new Handler(){21         public void handleMessage(android.os.Message msg) {22             if(msg.what == 0x1234){23                 Toast.makeText(MainActivity.this, msg.arg1 + "", 1000).show();24             }25         };26     };27     @Override28     protected void onCreate(Bundle savedInstanceState) {29         super.onCreate(savedInstanceState);30         setContentView(R.layout.activity_main);31         32         new Timer().schedule(new TimerTask() {33             int i = 0;34             @Override35             public void run() {36                 i++;37                 Message msg = new Message();38                 msg.what = 0x1234;39                 msg.arg1 = i;40                 hander.sendMessage(msg);41             }42         }, 0, 2000);43     }44     45 }

 

　　那麼，我們能不能通過Handler從主線程發送訊息給子線程呢？答案是肯定的，需要用到Looper.prepare()和Looper.loop()。如下面的代碼：

 1 public class MainActivity extends Activity { 2     EditText txt; 3     Button bt; 4     TestThread testThread; 5     int j = 0; 6      7     @Override 8     protected void onCreate(Bundle savedInstanceState) { 9         super.onCreate(savedInstanceState);10         setContentView(R.layout.activity_main);11         txt = (EditText) findViewById(R.id.txt);12         bt = (Button) findViewById(R.id.bn);13         testThread = new TestThread();14         testThread.start();15         bt.setOnClickListener(new OnClickListener() {16             17             @Override18             public void onClick(View arg0) {19                 j++;20                 Message msg = new Message();21                 msg.what = 0x1000;22                 msg.arg1 = j;23                 testThread.thander.sendMessage(msg);24             }25         });26         27         28     }29     30     //自訂子線程31     class TestThread extends Thread{32         public Handler thander;33         @Override34         public void run() {35             //建立一個Looper對象36             Looper.prepare();37             thander = new Handler(){38                 @Override39                 public void handleMessage(Message msg) {40                     if(msg.what == 0x1000){41                         System.out.println("j = " + msg.arg1);42                         //txt.setText(msg.arg1 + "");43                     }44                 }45             };46             //啟動Looper47             Looper.loop();48         }49     }50     51 }