Android中实现双缓冲（画板应用）和XML文件定义菜单

1.什么是双缓冲技术？双缓冲技术就是当用户操作界面完成后，会有一个缓冲区保存用户操作的结果。

为什么要使用双缓冲技术？拿Android 游戏开发来说，界面贞每次都是全部重画的，也就说画了新的，旧的就没了，所以需要使用双缓冲技术保存之前的内容。

如何实现双缓冲？使用一个Bitmap对象保留之前的画布即可。

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package com.example.phonegaptest;
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import android.content.Context;
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import android.graphics.Bitmap;
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import android.graphics.Bitmap.Config;
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import android.graphics.Canvas;
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import android.graphics.Color;
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import android.graphics.Paint;
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import android.graphics.Path;
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import android.util.AttributeSet;
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import android.view.MotionEvent;
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import android.view.View;
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public class DrawView extends View {
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    float preX;
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    float preY;
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    private Path path;
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    public Paint paint = null;
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    final int VIEW_WIDTH = 320;
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    final int VIEW_HEIGHT = 480;
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    Bitmap cacheBitmap = null;//定义一个内存中的图片，这张图片会作为缓冲区
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    Canvas cacheCanvas = null;//定义cacheBitmap上的画布cacheCanvas
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    public DrawView(Context context, AttributeSet set) {
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        super(context, set);
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        cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,
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                Config.ARGB_8888);//创建缓冲区
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        cacheCanvas = new Canvas();
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        path = new Path();
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        cacheCanvas.setBitmap(cacheBitmap);
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        paint = new Paint(Paint.DITHER_FLAG);
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        paint.setColor(Color.RED);
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        paint.setStyle(Paint.Style.STROKE);
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        paint.setStrokeWidth(1);
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        paint.setAntiAlias(true);
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        paint.setDither(true);
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    }
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    @Override
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    public boolean onTouchEvent(MotionEvent event) {
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        float x = event.getX();
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        float y = event.getY();
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        switch (event.getAction()) {
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        case MotionEvent.ACTION_DOWN:
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            path.moveTo(x, y);
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            preX = x;
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            preY = y;
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            break;
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        case MotionEvent.ACTION_MOVE:
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            path.quadTo(preX, preY, x, y);
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            preX = x;
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            preY = y;
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            break;
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        case MotionEvent.ACTION_UP:
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            cacheCanvas.drawPath(path, paint);
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            path.reset();
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            break;
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        }
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        invalidate();
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        return true;//返回true表明处理方法已经处理该事件，该事件不会扩散
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    }
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    @Override
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    protected void onDraw(Canvas canvas) {
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        super.onDraw(canvas);
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        Paint bmpPaint = new Paint();
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        canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);
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        canvas.drawPath(path, paint);
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    }
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}

2.XMl文件实现菜单功能

XMl文件如下：

<?xml version="1.0" encoding="utf-8"?>  
<menu xmlns:android="http://schemas.android.com/apk/res/android" >  
    <item  
        android:id="@+id/close"  
        android:icon="@drawable/ic_launcher"  
        android:orderInCategory="3"  
        android:title="Close"/>  
    <item  
        android:id="@+id/no_icon"  
        android:orderInCategory="2"  
        android:title="Sans Icon"/>  
    <item  
        android:id="@+id/disabled"  
        android:enabled="true"  
        android:orderInCategory="4"  
        android:title="Disabled"/>  
    <!-- orderInCategory表示的是item的排序-->  
    <group  
        android:id="@+id/other_stuff"  
        android:menuCategory="secondary"  
        android:visible="true" >  
        <item  
            android:id="@+id/later"  
            android:orderInCategory="0"  
            android:title="2nd-To-Last"/>  
        <item  
            android:id="@+id/last"  
            android:orderInCategory="1"  
            android:title="Last"/>  
    </group>  
    <!--表示的是二级菜单-->  
    <item  
        android:id="@+id/submenu"  
        android:orderInCategory="3"  
        android:title="A Submenu">  
        <menu>  
            <item  
                android:id="@+id/non_ghost"  
                android:alphabeticShortcut="n"  
                android:title="Non-Ghost"  
                android:visible="true"/>  
            <item  
                android:id="@+id/ghost"  
                android:alphabeticShortcut="g"  
                android:title="A Ghost"  
                android:visible="true"/>  
        </menu>  
    </item>  
  
</menu>

主文件

package com.example.receiveractivity;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
  
 
public class ReceiverActivity extends Activity {  
    /** Called when the activity is first created. */  
    private static final String TAG="BruceZhang";  
  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_receiver);  
  
    }  
  
    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        // TODO Auto-generated method stub  
        MenuInflater mflater=new MenuInflater(this);  
        mflater.inflate(R.menu.activity_receiver, menu);  
        return super.onCreateOptionsMenu(menu);  
    }  
  
    @Override  
    public boolean onOptionsItemSelected(MenuItem item) {  
        // TODO Auto-generated method stub  
        switch(item.getItemId()){  
        case R.id.close:  
            Log.v(TAG, "------------close");  
            break;  
        case R.id.no_icon:  
            Log.v(TAG, "------------noicon");  
            break;  
        case R.id.submenu:  
            Log.v(TAG, "------------submenu");  
            break;  
        case R.id.non_ghost:  
            Log.v(TAG, "------------non_ghost");  
            break;  
        case R.id.ghost:  
            Log.v(TAG, "------------ghost");  
            break;  
        case R.id.disabled:  
            Log.v(TAG, "------------disabled");  
            break;  
        case R.id.last:  
            Log.v(TAG, "------------last");  
            break;  
        case R.id.later:  
            Log.v(TAG, "------------laster");  
            break;  
        default:  
            break;  
        }  
        return super.onOptionsItemSelected(item);  
    }  
      
      
      
  
}