Android使用Handler的兩種方法

剛剛開始接觸android線程編程的時候，習慣好像java一樣，試圖用下面的代碼解決問題

 new Thread( new Runnable() {
    public void run() {
         myView.invalidate();
     }
}).start();

然而發現這樣是不行的，因爲它違背了單線程模型：Android UI操作並不是線程安全的並且這些操作必須在UI線程中執行。查閱了文檔和apidemo後，發覺常用的方法是利用Handler來實現UI線程的更新的。

 

下面代碼的功能很簡單：畫一個圓出來，每隔0.1秒，圓向10移動10個像素。但可以清楚展示利用Handler更新UI的流程。

 

 

 

首先創建簡單的View,代碼如下：

package com.ray.handler;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.view.View;

public class BounceView extends View {
    float x = 40;

    public BounceView(Context context) {
         super(context);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        x+=10;
        Paint mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(Color.GREEN);
        canvas.drawCircle(x, 40, 40, mPaint);
    }
}

創建Activity，代碼如下：

Java代碼

package com.ray.handler;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.Window;

public class TestHandler extends Activity {
     protected static final int GUIUPDATEIDENTIFIER = 0x101;

     Thread myRefreshThread = null;
     BounceView myBounceView = null;

     Handler myHandler = new Handler() {
          public void handleMessage(Message msg) {
               switch (msg.what) {
                    case TestHandler.GUIUPDATEIDENTIFIER:
                         myBounceView.invalidate();
                         break;
               }
               super.handleMessage(msg);
          }
     };
     public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          this.requestWindowFeature(Window.FEATURE_NO_TITLE);

          this.myBounceView = new BounceView(this);
          this.setContentView(this.myBounceView);
          new Thread(new myThread()).start();
     }

     class myThread implements Runnable {
          public void run() {
               while (!Thread.currentThread().isInterrupted()) {

                    Message message = new Message();
                    message.what = TestHandler.GUIUPDATEIDENTIFIER;

                    TestHandler.this.myHandler.sendMessage(message);
                    try {
                         Thread.sleep(100);
                    } catch (InterruptedException e) {
                         Thread.currentThread().interrupt();
                    }
               }
          }
     }
}

文字程序很簡單，一個View，一個Activity，利用handler和postInvalidate()更新UI。

程序效果是一個藍色的正方形向右移出屏幕。

package com.ray.test;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;

public class TestHandler extends Activity {
    private MyView myView;
    private Handler mHandler;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        myView = new MyView(this);
        mHandler = new Handler();
        mHandler.post(update);
        setContentView(myView);
    }

    private Runnable update = new Runnable() {
        public void run() {
            myView.update();
            mHandler.postDelayed(update, 5);
        }
    };

    class MyView extends View{

        private float x = 0f;
        public MyView(Context context) {
            super(context);

        }

        public void update(){
            postInvalidate();
        }
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            x+=1;
            Paint mPaint = new Paint();
            mPaint.setColor(Color.BLUE);
            canvas.drawRect(x, 40, x+40, 80, mPaint);
        }

    }
}