1.什麼是雙緩沖技術？雙緩沖技術就是當用戶操作界面完成後，會有一個緩沖區保存用戶操作的結果。
為什麼要使用雙緩沖技術？拿Android 遊戲開發來說，界面貞每次都是全部重畫的，也就說畫瞭新的，舊的就沒瞭，所以需要使用雙緩沖技術保存之前的內容。
如何實現雙緩沖？使用一個Bitmap對象保留之前的畫佈即可。
查看源碼打印?
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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;//定義一個內存中的圖片，這張圖片會作為緩沖區
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Canvas cacheCanvas = null;//定義cacheBitmap上的畫佈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);//創建緩沖區
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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表明處理方法已經處理該事件，該事件不會擴散
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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文件實現菜單功能
XMl文件如下：
[html] view plaincopy
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="https://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>
<!–表示的是二級菜單–>
<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
[java] view plaincopy
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; www.aiwalls.com
case R.id.later:
Log.v(TAG, "————laster");
break;
default:
break;
}
return super.onOptionsItemSelected(item);
}
}