Android simple draw

问题

Why it doesn't work ? I'm trying to "paint" where i put my finger, to write something. For example, when i am trying to make a C he looks like this: http://postimg.org/image/5obyif4o1/ ........................................................................

 public class BlackPixel extends View implements OnTouchListener{
    private Bitmap  mBitmap;
    Canvas mCanvas=new Canvas();
    Path    mPath=new Path();
    Paint   mBitmapPaint=new Paint(Paint.DITHER_FLAG);  
    Paint mPaint=new Paint();
    Paint circlePaint=new Paint();
    Path circlePath = new Path();

    Context context;

     @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);

    }


    public BlackPixel(Context context) {
        super(context);
        setFocusable(true);     
        setFocusableInTouchMode(true);
        this.setOnTouchListener(this);
    }



    @Override
    protected void onDraw(Canvas canvas)
    {       
        super.onDraw(canvas);

        canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);

        canvas.drawPath( mPath, mPaint );

        canvas.drawPath( circlePath,circlePaint  );
    }



//  @Override
    public boolean onTouch(View v, MotionEvent event) {

        float x=event.getX();
        float y=event.getY();


           int action = event.getAction();
            switch (action) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x,y);
                invalidate();
                return true;                

            case MotionEvent.ACTION_MOVE:
                touch_move(x,y);             
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up(x,y);
                invalidate();
                break;              
            }
            return true;
    }


    private void touch_start(float x, float y)
    {
           mPath.reset();
           mPath.moveTo(x, y);
           mX = x;
           mY = y;

    }

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


    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;
          }
    }


    private void touch_up(float x , float y)
    {
          mPath.lineTo(mX, mY);
          // commit the path to our offscreen
          mCanvas.drawPath(mPath, mPaint);
          // kill this so we don't double draw
          mPath.reset();

    }



    class Point
    {
        float x,y;
    }

回答1:

EDIT: this reflects changes you made in your code.

When you create mPaint, you're not setting its' style, which by default is FILL. Change it to STROKE. You can also set the stroke width. Do it in your constructor:

public BlackPixel(Context context) {
    super(context);
    setFocusable(true);     
    setFocusableInTouchMode(true);
    this.setOnTouchListener(this);

    //change paint style to STROKE
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeWidth(12);
}

Also, you can set the background color in onSizeChanged:

@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);
    //set background color
    mBitmap.eraseColor(0xFFAAAAAA);
    mCanvas = new Canvas(mBitmap);
}

Check FingerSample in Android SDK samples folder.

来源：https://stackoverflow.com/questions/20033736/android-simple-draw