如何在android中绘制用户在屏幕上绘制的矩形

Question

我想在屏幕上绘制矩形，我如何从用户触摸事件中获得绘制矩形的点?我用onTouchEvent和油漆画了一条线，如下所示。像这样，根据用户的需要绘制线条，我想绘制矩形，但是我无法得到这个的值。请帮助

public class SimpleDrawingView extends View {
private final int paintColor = Color.BLACK;
private Paint drawPaint;
private Path path = new Path();
float pointX;
float pointY;
public SimpleDrawingView(Context context, AttributeSet attrs) {
    super(context, attrs);
    setFocusable(true);
    setFocusableInTouchMode(true);
    setupPaint();
}
private void setupPaint() {
    // Setup paint with color and stroke styles
    drawPaint = new Paint();
    drawPaint.setColor(paintColor);
    drawPaint.setAntiAlias(true);
    drawPaint.setStrokeWidth(5);
    drawPaint.setStyle(Paint.Style.STROKE);
    drawPaint.setStrokeJoin(Paint.Join.ROUND);
    drawPaint.setStrokeCap(Paint.Cap.ROUND);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
     pointX = event.getX();
     pointY = event.getY();
    // Checks for the event that occurs
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            path.moveTo(pointX, pointY);
            return true;
        case MotionEvent.ACTION_MOVE:
            path.lineTo(pointX, pointY);
            break;
        default:
            return false;
    }
    // Force a view to draw again
    postInvalidate();
    return true;
}
@Override
protected void onDraw(Canvas canvas) {
    canvas.drawPath(path,drawPaint);
}

}

Answer 1

很简单:

Point2D p1 = null;
Point2D p2 = null;
@Override
public boolean onTouchEvent(MotionEvent event) {
     pointX = event.getX();
     pointY = event.getY();
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            p1 = new Point2D(pointX, pointY);
            return true;
        case MotionEvent.ACTION_UP:
            p2 = new Point2D(pointX, pointY);
            postInvalidate();
            break;
        default:
            return false;
    }
    return true;
}
@Override
protected void onDraw(Canvas canvas) {
    if(p1!=null && p2!=null) {
        canvas.drawRect(p1.getX(), p1.getY(), p2.getX(), p2.getY(), drawPaint);
        p1=null;
        p2=null;
    }
}

Answer 2

您也可以这样做

public class SimpleDrawingView extends View {
private final int paintColor = Color.BLACK;
private Paint drawPaint;
float pointX;
float pointY;
float startX;
float startY;
public SimpleDrawingView(Context context, AttributeSet attrs) {
super(context, attrs);
setFocusable(true);
setFocusableInTouchMode(true);
setupPaint();
}
private void setupPaint() {
// Setup paint with color and stroke styles
drawPaint = new Paint();
drawPaint.setColor(paintColor);
drawPaint.setAntiAlias(true);
drawPaint.setStrokeWidth(5);
drawPaint.setStyle(Paint.Style.STROKE);
drawPaint.setStrokeJoin(Paint.Join.ROUND);
drawPaint.setStrokeCap(Paint.Cap.ROUND);
}
@Override
 public boolean onTouchEvent(MotionEvent event) {
pointX = event.getX();
pointY = event.getY();
// Checks for the event that occurs
switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
        startX = pointX;
        startY = pointY;
        return true;
    case MotionEvent.ACTION_MOVE:
        break;
    default:
        return false;
}
// Force a view to draw again
postInvalidate();
return true;
}
 @Override
 protected void onDraw(Canvas canvas) {
 canvas.drawRect(startX, startY, pointX, pointY, drawPaint);
  }
}