第十一节--Handler的基本应用_handler<>的测试用例-优快云博客

本文深入解析了Android中Handler的工作原理及应用案例，包括如何通过Handler实现线程间通信，更新UI，以及定时任务等。

Handler：

java.lang.Object
↳	android.os.Handler

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。

代码示例：

主Activity public 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() { @Override public void onClick(View v) { Intent intent=new Intent(); intent.setClass(HandlerTest.this, HandlerTest_One.class); startActivity(intent); } }); button2.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(); intent.setClass(HandlerTest.this, HandlerTest_Two.class); startActivity(intent); } }); } }

//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);
        }   
           
    }   
}

//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() {
			
			@Override
			public 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);   
            }   
        }   
    };   
}

<?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>

演示效果：