如何使用多条线绘制自定义形状

Question

我想用多条直线绘制自定义形状。为此，我使用了画布。但我只能画一条线。当我画第二个时，前面消失了。我的代码被给出。

public class CanvasBackground extends View {
public Paint paint;
public Context context;
public Canvas canvas;
public ScaleGestureDetector scaleGestureDetector;
float scalfactor = 1f;
boolean isDrawing;
private PointF startPoint, endPoint;
public CanvasBackground(Context context) {
    super(context);
    this.context = context;
    paint = new Paint();
    scaleGestureDetector = new ScaleGestureDetector(context, new CanvasScale());
    setDrawingCacheEnabled(true);
}
@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    this.canvas = canvas;
    paint.setColor(Color.WHITE);
    canvas.drawPaint(paint);
    canvas.save();
    DrawingZoomingCanvas(canvas);
    DrawingLine(canvas);
    canvas.restore();
    Log.e("OnDraw >>>", "CALLING");
}
@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            startPoint = new PointF(event.getX(), event.getY());
            endPoint = new PointF();
            isDrawing = true;
            break;
        case MotionEvent.ACTION_MOVE:
            if (isDrawing) {
                endPoint.x = event.getX();
                endPoint.y = event.getY();
                invalidate();
            }
            break;
        case MotionEvent.ACTION_UP:
            if (isDrawing) {
                endPoint.x = event.getX();
                endPoint.y = event.getY();
                //isDrawing = false;
                invalidate();
            }
            break;
        default:
            break;
    }
    //scaleGestureDetector.onTouchEvent(event);
    Log.e("OnTouch >>>", "CALLING" + isDrawing);
    return true;
}
//drawing Matrix Canvas With Zoom
private void DrawingZoomingCanvas(Canvas canvas) {
    //drawing Matarix
    canvas.translate(scalfactor * 10, scalfactor * 10);
    canvas.scale(scalfactor, scalfactor);
    paint.setColor(Color.rgb(220, 220, 220));
    for (int i = 0; i <= canvas.getHeight() * scalfactor; i += 10) {
        canvas.drawLine(i, 0, i, canvas.getHeight(), paint);
        canvas.drawLine(0, i, canvas.getWidth(), i, paint);
    }
}
//drawing a line
private void DrawingLine(Canvas canvas) {
    paint = new Paint();
    paint.setColor(Color.RED);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(2);
    paint.setAntiAlias(true);
    if (isDrawing)
        canvas.drawLine(startPoint.x, startPoint.y, endPoint.x, endPoint.y, paint);
}
private class CanvasScale extends ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        scalfactor *= scaleGestureDetector.getScaleFactor();
        scalfactor = Math.max(0.1f, Math.min(scalfactor, 10.0f));
        invalidate();
        return true;
    }
}
}

Answer 1

每次绘制线条时，您都会清除画布，因此在绘制新线条时，前一条线条将被擦除。

您需要将以前的线条存储在位图中，以便在绘制新线条时可以绘制这些线条。