如何在用户在Android屏幕上绘制时绘制矩形答案

【问题标题】：How to draw rectangle as user draws on screen in android如何在用户在Android屏幕上绘制时绘制矩形
【发布时间】：2016-10-24 19:20:07
【问题描述】：

我想根据用户的需要在屏幕上绘制矩形，如何从用户触摸事件中获取绘制矩形的点？我已经使用 onTouchEvent 画线并绘制如下。像这样，根据用户的需要画线我想画矩形，但我无法得到这个值。请帮忙

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);

}

}

【问题讨论】：

您好，您在使用 Canvas 吗？
我想请你先把问题说清楚。您想通过编程或手指在屏幕上四舍五入来绘制矩形？
@android_softy 我想通过在屏幕上用四舍五入的手指来绘制矩形。谢谢你的支持。下面的答案解决了问题

标签： android touch drawing drawrectangle

【解决方案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;
    }
}

【讨论】：

谢谢。我用另一种方式做到了，我不知道哪个更好。当 ACTION_DOWN 和宽度和高度使用 pointX 和 pointY 时，我将起点分配给两个浮点变量，` ... @Override public boolean onTouchEvent(MotionEvent event) { pointX = event.getX(); pointY = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: startX = pointX; startY = pointY; ... protected void onDraw(Canvas canvas) { canvas.drawRect(startX, startY, pointX, pointY, drawPaint); } ...`
我展示了一个示例代码。我很高兴你能够改进它。

【解决方案2】：

你也可以这样做

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);
  }
}

【讨论】：