第十一节--Handler的基本应用

Handler：

java.lang.Object   ↳android.os.Handler

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原意：

A Handler allows you to send and process Message and Runnable objects associated with a thread's MessageQueue.

译文：

Handler允许我们去发送和处理信息，并且线程对象是和信息队列有联系的。handler主要负责子线程的单独运行，同时可以更新主线程的UI。

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代码示例：

主Activitypublic class HandlerTest extends Activity { private Button button1,button2; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); button1=(Button)findViewById(R.id.Button01); button2=(Button)findViewById(R.id.Button02); button1.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent intent=new Intent();intent.setClass(HandlerTest.this, HandlerTest_One.class);startActivity(intent);}}); button2.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent intent=new Intent();intent.setClass(HandlerTest.this, HandlerTest_Two.class);startActivity(intent);}}); } }

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主布局文件main.xml<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" ><TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Handler test" /><Button android:text="Handler测试1" android:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button><Button android:text="Handler测试2" android:id="@+id/Button02" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button></LinearLayout>

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//第一个Handler测试例子public class HandlerTest_One extends Activity { private MyView myView; private Handler mHandler; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); myView = new MyView(this); //执行某个Runnanble(使用POST方法) mHandler = new Handler(); //添加一个线程进入栈中，并行执行一个线程 mHandler.post(update); setContentView(myView); } private Runnable update = new Runnable() { public void run() { myView.update(); //每隔一秒钟，相当于执行一次mHandler.post(update) mHandler.postDelayed(update, 1000); } }; class MyView extends View{ private float x = 0f; public MyView(Context context) { super(context); } public void update(){ //起到刷新屏幕的效果，有点像之前学过的repaint //调用invalidate或者postInvalidate方法就会执行onDraw方法 postInvalidate(); } protected void onDraw(Canvas canvas) { super.onDraw(canvas); String text="移动的图形"; x+=1; Paint mPaint = new Paint(); //设置字体 String familyName = "宋体"; Typeface font = Typeface.create(familyName,Typeface.BOLD); mPaint.setTypeface(font); mPaint.setTextSize(22); //设置颜色 mPaint.setColor(Color.RED); //绘制内容 canvas.drawText(text, 40, 20, mPaint); canvas.drawRect(x, 40, x+40, 80, mPaint); mPaint.setColor(Color.YELLOW); // canvas.drawOval(null, mPaint); canvas.drawCircle(x, 150,15, mPaint); } } }

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//第二个Handler测试public class HandlerTest_Two extends Activity {private Button startbutton,stopbutton; private ProgressBar progressBar; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_two); startbutton = (Button)findViewById(R.id.startButton); stopbutton = (Button)findViewById(R.id.stopButton); progressBar = (ProgressBar)findViewById(R.id.progressBar); startbutton.setOnClickListener(new BtOnClickListener()); stopbutton.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {handler.removeCallbacks(updateThread);}}); } //内部类，响应Button的单击事件 class BtOnClickListener implements View.OnClickListener{ public void onClick(View v) { progressBar.setVisibility(View.VISIBLE); handler.post(updateThread); } } //匿名内部类，复写handlerMessage方法 ，目的是接受传送过来的信息 Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { progressBar.setProgress(msg.arg1); handler.post(updateThread); } }; //匿名内部线程类，覆写run方法 Runnable updateThread = new Runnable(){ int i = 0 ; public void run() { // TODO Auto-generated method stub System.out.println("Begin "); i = i + 10; Message msg = handler.obtainMessage(); msg.arg1 = i; try { Thread.sleep(2000); } catch (Exception e) { // TODO: handle exception } //当我们执行方法会自动把信息添加到Message队列当中，与此会调用上面的handleMessage(Message msg)方法 handler.sendMessage(msg); if (i == 100) { handler.removeCallbacks(updateThread); } } }; }

<!--第二个测试的布局文件 --><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ProgressBar android:id="@+id/progressBar" style="?android:attr/progressBarStyleHorizontal" mce_style="?android:attr/progressBarStyleHorizontal" android:layout_width="200dp" android:layout_height="wrap_content" android:visibility="gone" /> <Button android:id="@+id/startButton" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="开始" /> <Button android:id="@+id/stopButton" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="停止" /> </LinearLayout>

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演示效果：