如何在Android中绘制一个圆圈并移动它/拖动它

Posted 2023-02-26

【中文标题】如何在Android中绘制一个圆圈并移动它/拖动它

【英文标题】：How to draw a circle and move it / drag it on touch in Android

【发布时间】：2012-09-24 11:27:33

【问题描述】：

在我的应用程序中，我需要画一个圆圈，用户可以将它拖到屏幕上的任何位置。

为此，我创建了一个视图，在onDraw 方法中绘制了圆圈。我尝试使用onTouchEvent 跟踪运动。但是当我尝试拖动圆圈时，圆圈并没有真正移动，而是在我触摸屏幕的任何地方创建一个新圆圈。

请有人帮我解决我缺少的问题。

这是我的代码

public class Circle extends View 

Paint paint, paintSmall;
private Point start = null;
private Point cursorAtMouseDown = null;
private Point startAtMouseDown = null;
private Point endAtMouseDown = null;
private boolean movingStart = false;
private boolean movingEnd = false;
private boolean movingLine = false;

public Circle(Context context) 
    super(context);
    init();


public Circle(Context context, AttributeSet attrs) 
    super(context, attrs);
    init();


public Circle(Context context, AttributeSet attrs, int defStyle) 
    super(context, attrs, defStyle);
    init();


private void init() 
    paint = new Paint();
    start = new Point(100, 100);
    paint.setColor(Color.BLUE);
    paint.setStrokeWidth(10);
    paint.setStyle(Paint.Style.STROKE);



@Override
protected void onDraw(Canvas canvas) 
    super.onDraw(canvas);
    paint.setStyle(Paint.Style.STROKE);
    canvas.drawCircle(start.x, start.y, 80, paint);

    canvas.drawCircle(start.x, start.y, 10, paint);



@Override
public boolean onTouchEvent(MotionEvent event) 

    Log.d("Inside On Touch", "");
    switch (event.getAction()) 
    case MotionEvent.ACTION_UP:

        if (movingStart || movingEnd || movingLine) 
            invalidate();
        

        movingStart = false;
        movingEnd = false;
        movingLine = false;
        break;
    case MotionEvent.ACTION_OUTSIDE:
        if (movingStart || movingEnd || movingLine) 
            invalidate();
        

        movingStart = false;
        movingEnd = false;
        movingLine = false;
        break;
    case MotionEvent.ACTION_MOVE:

        Log.d("Inside On Touch", "ACTION_MOVE");

        if (movingStart) 
            start.x = (int) event.getX();
            start.y = (int) event.getY();
            invalidate();
            Log.d("Inside On Touch", "--movingStart=" + movingStart);
            return true;
         else if (movingEnd) 
            start.x = (int) event.getX();
            start.y = (int) event.getY();
            invalidate();
            Log.d("Inside On Touch", "--movingEnd=" + movingEnd);
            return true;
         else if (movingLine) 
            Log.d("Inside On Touch", "--movingLine=" + movingLine);
            if (cursorAtMouseDown != null) 
                // double diffX = event.getX() - cursorAtMouseDown.x;
                // double diffY = event.getY() - cursorAtMouseDown.y;
                // start.x = (int) (startAtMouseDown.x + diffX);
                // start.y = (int) (startAtMouseDown.y + diffY);

                start = cursorAtMouseDown;

                invalidate();
                return true;
            

        
        return false;

    case MotionEvent.ACTION_DOWN:
        cursorAtMouseDown = new Point((int) event.getX(),
                (int) event.getY());

        if (cursorAtMouseDown.equals(start)) 

        

        if (isCircleCenterChaged(cursorAtMouseDown)) 
            movingLine = true;
        

        return true;

    default:
        return super.onTouchEvent(event);

    
    return false;

【问题讨论】：

您介意分享代码吗？

【参考方案1】：

我不确定，但是如果您管理以下变量，那么它可以解决您的问题：

private Point cursorAtMouseDown = null; 
private Point startAtMouseDown = null; 
private Point endAtMouseDown = null; 
private boolean movingStart = false; 
private boolean movingEnd = false; 
private boolean movingLine = false; 

请管理布尔变量和鼠标移动。

【参考方案2】：

我不完全确定使用movingLine、movingEnd 和movingStart 标志是什么意思；但是似乎movingEnd和movingStart标志从未设置为true。因此，它们对应的 onTouch() 代码块永远不会被访问。