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