Question

我创建了一个扩展ImageView的类，允许我在触摸时在ImageView上绘制矩形。

我可以绘制矩形，但只有在我从起点向下和向右拖动矩形时才会显示。

如果我将矩形从起点向上或向左拖动，则不会绘制矩形。 OnDraw（）会触发，但不会显示任何内容。

我的课程：

public class TagImageView extends ImageView {

    private float downX;
    private float downY;
    private float upX;
    private float upY;
    private Paint paint;

    public TagImageView(Context context) {
        super(context);   
        init();
    }

    public TagImageView(Context context, AttributeSet attrs) {
        super(context, attrs);     
        init();
    }

    public TagImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(3);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        switch (action) {
        case MotionEvent.ACTION_DOWN:   
            downX = event.getX();
            downY = event.getY();
            invalidate();            

            return true;
        case MotionEvent.ACTION_MOVE:
            upX = event.getX();
            upY = event.getY();
            invalidate();

            return true;
        case MotionEvent.ACTION_UP:
            invalidate();

            return true;
        case MotionEvent.ACTION_CANCEL:
            break;
        default:
            break;
        }      

        return super.onTouchEvent(event);
    }

    @Override
    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawRect(downX, downY, upX, upY, paint);
    }
}

编辑：不确定这是否相关？ https://stackoverflow.com/a/24168545/2380071

Answer 1

好吧，我刚刚修改了我的OnDraw()方法来检查downX，downY和upX，upY点的值。琐碎，真的......虽然不确定它是否最有效率。欢迎任何建议（或者，呃..指针）！

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    if (downX < upX && downY < upY)
        canvas.drawRect(downX, downY, upX, upY, paint);
    else if (downX > upX && downY < upY)
        canvas.drawRect(upX, downY, downX, upY, paint);
    else if (downX < upX && downY > upY)
        canvas.drawRect(downX, upY, upX, downY, paint);
    else
        canvas.drawRect(upX, upY, downX, downY, paint);
}

在ImageView上绘制矩形 - 不向上/向左绘制

1 个答案: