Looper物件之角色(Demo 2)

由別的線程送訊息到主線程的Message Queue
Java代码 
package com.example.ac01;  
 
import android.app.Activity;  
import android.graphics.Color;  
import android.os.Bundle;  
import android.os.Handler;  
import android.os.Looper;  
import android.os.Message;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
import android.widget.LinearLayout;  
import android.widget.TextView;  
 
//由別的線程送訊息到主線程的Message Queue  
public class ac02 extends Activity implements OnClickListener {  
    private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT;  
    private final int FP = LinearLayout.LayoutParams.FILL_PARENT;  
    public TextView tv;  
    private myThread t;  
    private Button btn, btn2;  
 
    public void onCreate(Bundle icicle) {  
        super.onCreate(icicle);  
        LinearLayout layout = new LinearLayout(this);  
        layout.setOrientation(LinearLayout.VERTICAL);  
        btn = new Button(this);  
        btn.setId(101);  
 
        btn.setBackgroundResource(R.drawable.icon);  
        btn.setText("test looper");  
        btn.setOnClickListener(this);  
        LinearLayout.LayoutParams param = new LinearLayout.LayoutParams(100, 50);  
        param.topMargin = 10;  
        layout.addView(btn, param);  
        btn2 = new Button(this);  
        btn2.setId(102);  
        btn2.setBackgroundResource(R.drawable.icon);  
        btn2.setText("exit");  
        btn2.setOnClickListener(this);  
        layout.addView(btn2, param);  
        tv = new TextView(this);  
        tv.setTextColor(Color.WHITE);  
        tv.setText("");  
        LinearLayout.LayoutParams param2 = new LinearLayout.LayoutParams(FP, WC);  
        param2.topMargin = 10;  
        layout.addView(tv, param2);  
        setContentView(layout);  
    }  
 
    public void onClick(View v) {  
        switch (v.getId()) {  
        case 101:  
            t = new myThread();  
            t.start();  
            break;  
        case 102:  
            finish();  
            break;  
        }  
    }  
 
    // ------------------------------------------------------  
    class EHandler extends Handler {  
        public EHandler(Looper looper) {  
            super(looper);  
        }  
 
        @Override 
        public void handleMessage(Message msg) {  
            tv.setText((String) msg.obj);  
        }  
    }  
 
    // ------------------------------------------------------  
    class myThread extends Thread {  
        private EHandler mHandler;  
 
        // Android會自動替主線程建立Message Queue  
        // 在這個子線程裡並沒有建立Message Queue  
        // 所以，myLooper值為null，而mainLooper則指向主線程裡的Looper物件  
        public void run() {  
            Looper myLooper, mainLooper;  
            myLooper = Looper.myLooper();  
            mainLooper = Looper.getMainLooper();  
            String obj;  
            if (myLooper == null) {  
                // 此mHandler屬於主線程  
                // 这里我们可以这样理解:因为根据demo1中的形象比喻,如果这个机构的传话员,跟这个Looper部门  
                // 应该属于同一个线程才符合情理  
                mHandler = new EHandler(mainLooper);  
                obj = "current thread has no looper!";  
            } else {  
                mHandler = new EHandler(myLooper);  
                obj = "This is from current thread.";  
            }  
            mHandler.removeMessages(0);  
            Message m = mHandler.obtainMessage(1, 1, 1, obj);  
            mHandler.sendMessage(m);  
        }  
    }  
}  
// ------------------------------------------------------- 


代码中已经做了很详细的解释,有疑问的我们可以一起探讨