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

/Files/foura/looper_2.rar