线程处理UI的理解Demo

这个例子对于子线程不能处理UI线程的View可以有助于了解:

package com.example;

import android.app.Activity;
import android.content.Context;
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;

/*介紹過Android主線程與子線程之溝通。所謂主線程通常是UI線程。
 * Android的UI是單線程(Single-threaded)的。為了避免拖住GUI，
 * 一些較費時的物件應該交給獨立的線程去執行。如果幕後的線程來執行UI物件，
 * Android就會發出錯誤訊息CalledFromWrongThreadException 
 * 基本上，Android希望UI thread能夠給予User做快速的反應。
 * 如果UI thread花費太多時間做幕後的事情，超過5秒鐘，Android就會給user提示
 */

public class Looper_6 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;
	private Handler h;
	private Context ctx;

	public void onCreate(Bundle icicle) {
		super.onCreate(icicle);
		ctx = this;
		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);
		// ------------------------
		t = new myThread();
		t.start();
	}

	public void onClick(View v) {
		switch (v.getId()) {
		case 101:
			try {
				Thread.sleep(8000);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			String obj = "mainThread";
			Message m = h.obtainMessage(1, 1, 1, obj);
			h.sendMessage(m);
			break;
		case 102:
			h.getLooper().quit();
			finish();
			break;
		}
	}

	public class EventHandler extends Handler {
		public EventHandler(Looper looper) {
			super(looper);
		}

		@Override
		public void handleMessage(Message msg) {
			tv.setText((String) msg.obj);
		}
	}

	class myThread extends Thread {
		final boolean TEST_FLAG = false;

		public void run() {
			Looper.prepare();
			h = new Handler() {
				public void handleMessage(Message msg) {
					if (TEST_FLAG)
						// tv物件是主線程誕生的UI物件
						// 如果子線程也去插手的話，Android程式就停止了
						tv.setText("myThread is running");
					else {
						EventHandler ha = new EventHandler(Looper
								.getMainLooper());
						String obj = (String) msg.obj + ", myThread";
						Message m = ha.obtainMessage(1, 1, 1, obj);
						ha.sendMessage(m);
					}
				}
			};
			Looper.loop();
		}
	}
}

评论

1 楼 edison_cool911 2010-08-01  

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