线程处理UI的理解Demo

edison_cool911

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 blocke.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);}@Overridepublic 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();}}}