4、釋放記憶體緩衝區

下面的例子(一個畫圖板)將實現雙緩衝畫圖

先自定義一個View(Bitmap將會繪製到這個View上)

package Wangli.Graphics.HandDraw;import android.content.Context;import
 
 android.graphics.Bitmap;import android.graphics.Bitmap.Config;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Path;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;public class DrawView extends
 
 View {    float preX;    float preY;    private Path path;    public Paint paint = null;    final int VIEW_WIDTH = 320;    final int VIEW_HEIGHT = 480;    //定義一個記憶體中的圖片,該圖片將作為緩衝區    Bitmap cacheBitmap = null;    //定義cacheBitmap上的canvas物件    Canvas cacheCanvas = null; public DrawView(Context context, AttributeSet attrs)
 
 {  super(context, attrs);  //建立一個與該View相同大小的快取區  cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH,VIEW_HEIGHT,Config.ARGB_8888);  cacheCanvas = new Canvas();  path = new Path();  //設定cacheCanvas將會繪製到記憶體中的cacheBitmap上  cacheCanvas.setBitmap(cacheBitmap);  //設定畫筆的顏色  paint = new Paint(Paint.DITHER_FLAG);  paint.setColor(Color.RED);  //設定畫筆的風格  paint.setStyle(Paint.Style.STROKE);  paint.setStrokeWidth(1);  //反鋸齒  paint.setAntiAlias(true);  paint.setDither(true); }    public boolean onTouchEvent(MotionEvent event)    {     //獲取拖動事件發生的位置     float x = event.getX();     float y = event.getY();     switch(event.getAction())     {         case MotionEvent.ACTION_DOWN:           path.moveTo(x, y);           preX = x;           preY = y;           break;         case MotionEvent.ACTION_MOVE:              path.quadTo(preX, preY, x, y);              preX = x;              preY = y;              break;         case MotionEvent.ACTION_UP:           cacheCanvas.drawPath(path, paint);           path.reset();           break;     }     invalidate();     //返回true表明處理方法已經處理該事件     return true;    }    public void onDraw(Canvas canvas)    {     Paint bmpPaint = new Paint();     //將cacheBitmap繪製到該View元件上     canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);     //沿著path繪製     canvas.drawPath(path, paint);    }}

<?xml version="1.0" encoding="utf-8"?><menu xmlns:android="http://schemas.android.com/apk/res/android"> <item android:title="@string/color">  <menu>   <!-- 定義一組單選選單項 -->   <group android:checkableBehavior="single">    <!-- 定義多個選單項 -->    <item     android:id="@+id/red" android:title="@string/color_red"/>    <item     android:id="@+id/green" android:title="@string/color_green"/>    <item     android:id="@+id/blue" android:title="@string/color_blue"/>   </group>  </menu> </item> <item android:title="@string/width">  <menu>   <!-- 定義一組選單項 -->   <group>    <!-- 定義3個選單項 -->    <item     android:id="@+id/width_1" android:title="@string/width_1"/>    <item     android:id="@+id/width_3" android:title="@string/width_3"/>    <item     android:id="@+id/width_5" android:title="@string/width_5"/>         </group>  </menu> </item> <item  android:id="@+id/blur" android:title="@string/blur"/>  <item  android:id="@+id/emboss" android:title="@string/emboss"/>       </menu>

<?xml version="1.0" encoding="utf-8"?><resources>  <string name="hello">Hello World, HandDraw!</string>   <string name="app_name">手繪</string>   <string name="width_1">1畫素</string>   <string name="width_3">3畫素</string>   <string name="width_5">5畫素</string>   <string name="color_red">紅色</string>   <string name="color_green">綠色</string>   <string name="color_blue">藍色</string>   <string name="color">畫筆顏色</string>   <string name="width">畫筆寬度</string>   <string name="blur">模糊效果</string>   <string name="emboss">浮雕效果</string> </resources>

package Wangli.Graphics.HandDraw;import android.app.Activity;import android.graphics.BlurMaskFilter;import android.graphics.Color;import android.graphics.EmbossMaskFilter;import android.os.Bundle;import android.view.Menu;import android.view.MenuInflater;import android.view.MenuItem;public class HandDraw extends Activity {    /** Called when the activity is first created. */ EmbossMaskFilter emboss; BlurMaskFilter blur;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        emboss = new EmbossMaskFilter(new float[]{1.5f,1.5f,1.5f},0.6f,6,4.2f);        blur = new BlurMaskFilter(8,BlurMaskFilter.Blur.NORMAL);    }    //負責建立選項選單    public boolean onCreateOptionsMenu(Menu menu)    {     MenuInflater inflator = new MenuInflater(this);     //狀態R.menu.context對應選單,並新增到中     inflator.inflate(R.menu.my_menu,menu);     return super.onCreateOptionsMenu(menu);    }    //選單項被單擊後的回撥方法    public boolean onOptionsItemSelected(MenuItem mi)    {     DrawView dv = (DrawView)findViewById(R.id.draw);     //判斷單擊的是哪個選單項,並有針對性地做出響應     switch(mi.getItemId())     {         case R.id.red:          dv.paint.setColor(Color.RED);          mi.setChecked(true);          break;         case R.id.green:          dv.paint.setColor(Color.GREEN);          mi.setChecked(true);          break;         case R.id.blue:          dv.paint.setColor(Color.BLUE);          mi.setChecked(true);          break;         case R.id.width_1:          dv.paint.setStrokeWidth(1);          mi.setChecked(true);          break;         case R.id.width_3:          dv.paint.setStrokeWidth(3);          mi.setChecked(true);          break;         case R.id.width_5:          dv.paint.setStrokeWidth(5);          mi.setChecked(true);          break;         case R.id.blur:          dv.paint.setMaskFilter(blur);          mi.setChecked(true);          break;         case R.id.emboss:          dv.paint.setMaskFilter(emboss);          mi.setChecked(true);          break;     }     return true;    }}

更改畫筆效果