onDraw優化，如何增加perfomace？

Question

我想繪製我的.png圖像，但它的工作速度非常慢。如果我在沒有.png文件的情況下繪製imageView，它可以正常工作。我該如何解決這個問題？據我所知，我需要防止「大量的圖紙」，我怎麼能意識到這一點？

代碼：

public class Draw 
    extends Activity{ 

DrawingView dv ; 
private Paint  mPaint; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    dv = new DrawingView(this); 
    setContentView(dv); 
    mPaint = new Paint(); 
    mPaint.setAntiAlias(true); 
    mPaint.setDither(true); 
    mPaint.setColor(Color.GREEN); 
    mPaint.setStyle(Paint.Style.STROKE); 
    mPaint.setStrokeJoin(Paint.Join.ROUND); 
    mPaint.setStrokeCap(Paint.Cap.ROUND); 
    mPaint.setStrokeWidth(12); 
} 

public class DrawingView extends View { 

    public int width; 
    public int height; 
    private Bitmap mBitmap; 
    private Canvas mCanvas; 
    private Path mPath; 
    private Paint mBitmapPaint; 
    Context context; 
    private Paint circlePaint; 
    private Path circlePath; 

    public DrawingView(Context c) { 
     super(c); 
     context=c; 
     mPath = new Path(); 
     mBitmapPaint = new Paint(Paint.DITHER_FLAG); 
     circlePaint = new Paint(); 
     circlePath = new Path(); 
     circlePaint.setAntiAlias(true); 
     circlePaint.setColor(Color.BLUE); 
     circlePaint.setStyle(Paint.Style.STROKE); 
     circlePaint.setStrokeJoin(Paint.Join.MITER); 
     circlePaint.setStrokeWidth(4f); 


    } 

    @Override 
    protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
     super.onSizeChanged(w, h, oldw, oldh); 

     mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888); 
     mCanvas = new Canvas(mBitmap); 

    } 
    @Override 
    protected void onDraw(Canvas canvas) { 
     super.onDraw(canvas); 
     Bitmap bm = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory() + "/MANUAL/workflow" + "/img.png"); 
     int targetWidth = bm.getWidth()/1; 
     int targetHeight = bm.getHeight()/1; 
     Matrix matrix = new Matrix(); 
     matrix.postScale(0.7f, 0.65f); 
     Bitmap size = Bitmap.createBitmap(bm, 0, 0, targetWidth, targetHeight, matrix, true); 
     Paint paint = new Paint(); 
     paint.setColor(Color.RED); 
     canvas.drawBitmap(size, 0, 0, paint); 

     canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint); 
     canvas.drawPath(mPath, mPaint); 
     canvas.drawPath(circlePath, circlePaint); 
    } 

    private float mX, mY; 
    private static final float TOUCH_TOLERANCE = 4; 

    private void touch_start(float x, float y) { 
     mPath.reset(); 
     mPath.moveTo(x, y); 
     mX = x; 
     mY = y; 
    } 
    private void touch_move(float x, float y) { 
     float dx = Math.abs(x - mX); 
     float dy = Math.abs(y - mY); 
     if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) { 
      mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2); 
      mX = x; 
      mY = y; 

      circlePath.reset(); 
      circlePath.addCircle(mX, mY, 30, Path.Direction.CW); 
     } 
    } 
    private void touch_up() { 
     mPath.lineTo(mX, mY); 
     circlePath.reset(); 
     // commit the path to our offscreen 
     mCanvas.drawPath(mPath, mPaint); 
     // kill this so we don't double draw 
     mPath.reset(); 
    } 

    @Override 
    public boolean onTouchEvent(MotionEvent event) { 
     float x = event.getX(); 
     float y = event.getY(); 

     switch (event.getAction()) { 
      case MotionEvent.ACTION_DOWN: 
       touch_start(x, y); 
       invalidate(); 
       break; 
      case MotionEvent.ACTION_MOVE: 
       touch_move(x, y); 
       invalidate(); 
       break; 
      case MotionEvent.ACTION_UP: 
       touch_up(); 
       invalidate(); 
       break; 
     } 
     return true; 
    } 
} 

Answer 1

你的onDraw（）方法應該是這樣的：

@Override 
protected void onDraw(Canvas canvas) { 

    paint.setColor(Color.RED); 
    canvas.drawBitmap(size, 0, 0, paint); 
    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint); 
    canvas.drawPath(mPath, mPaint); 
    canvas.drawPath(circlePath, circlePaint); 
} 

所有的位圖解碼和調整應在外部進行（在構造函數或僅在視圖大小），每次當結果每次都相同時，不需要解碼和調整它的大小。