Looper物件之角色(Demo 2)

由別的線程送訊息到主線程的Message Queue

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
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