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?01package com.example.phonegaptest;02
03import android.content.Context;04import android.graphics.Bitmap;05import android.graphics.Bitmap.Config;06import android.graphics.Canvas;07import android.graphics.Color;08import android.graphics.Paint;09import android.graphics.Path;10import android.util.AttributeSet;11import android.view.MotionEvent;12import android.view.View;13
14public class DrawView extends View {15 float preX;16 float preY;17 private Path path;18 public Paint paint = null;19 final int VIEW_WIDTH = 320;20 final int VIEW_HEIGHT = 480;21 Bitmap cacheBitmap = null;//定义一个内存中的图片，这张图片会作为缓冲区22 Canvas cacheCanvas = null;//定义cacheBitmap上的画布cacheCanvas23
24 public DrawView(Context context, AttributeSet set) {25 super(context, set);26 cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,27 Config.ARGB_8888);//创建缓冲区28 cacheCanvas = new Canvas();29
30 path = new Path();31 cacheCanvas.setBitmap(cacheBitmap);32
33 paint = new Paint(Paint.DITHER_FLAG);34 paint.setColor(Color.RED);35 paint.setStyle(Paint.Style.STROKE);36 paint.setStrokeWidth(1);37 paint.setAntiAlias(true);38 paint.setDither(true);39 }40
41 @Override42 public boolean onTouchEvent(MotionEvent event) {43 float x = event.getX();44 float y = event.getY();45
46 switch (event.getAction()) {47 case MotionEvent.ACTION_DOWN:48 path.moveTo(x, y);49 preX = x;50 preY = y;51 break;52 case MotionEvent.ACTION_MOVE:53 path.quadTo(preX, preY, x, y);54 preX = x;55 preY = y;56 break;57 case MotionEvent.ACTION_UP:58 cacheCanvas.drawPath(path, paint);59 path.reset();60 break;61 }62 invalidate();63 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64 }65
66 @Override67 protected void onDraw(Canvas canvas) {68 super.onDraw(canvas);69 Paint bmpPaint = new Paint();70 canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);71 canvas.drawPath(path, paint);72 }73
74}




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);      }                      }  

1楼MaSurQ前天 15:36

相当好 ，学习中