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。
查看源码打印?
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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：
[html] view plaincopy
<?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:or
补充：移动开发 , Android ,
