android - Android 开发卡在绘画/绘图上

Question

我想要完成的事情很简单。制作一个非常基本和/或原始的绘图应用程序。没有改变画笔大小，没有改变颜色或类似的东西，只是一个简单的绘图应用程序，就像你在一张简单的纸上画画一样。

我知道 Canvas 和 Paint 但不确定如何实现我提到的免费绘图概念。任何帮助将不胜感激。

@Override
    protected void onDraw(Canvas canvas) {
    Paint p = new Paint();

    p.setColor(Color.BLUE);

    int width = getWidth();
    int height = getHeight();

    canvas.drawLine(0, 0, width, height, p);
}

Answer 1

你的类必须扩展视图。您覆盖 onDraw(canvas) 以绘制路径。您覆盖 onTouch(event) 并调用 invalidate 来刷新绘图。您使用路径来绘制。

public class MainActivity extends Activity {

DrawingView dv ;
RelativeLayout rl;   
private Paint       mPaint;
private DrawingManager mDrawingManager=null;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dv = new DrawingView(this); // custom view
    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);  // paint thickness
}

 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(); // path used to draw
        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); 
                  // draw a circle when user touch and move.  
        }

        @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);

        canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);    
        canvas.drawPath( mPath,  mPaint); // draw the path
        canvas.drawPath( circlePath,  circlePaint); //draw the circle
        }

        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) { // touch events
        float x = event.getX();
        float y = event.getY();

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

}