UIView在圓形路徑中移動（不是動畫）

Question

我有UIView，我必須在圓形路徑中移動它。

Answer 1

簡單。將UIImageView添加到UIView的子類，該子類具有圖像的屬性，以便您可以在代碼中移動它。實現touchesBegan：... touchesMoved：...和touchesEnded：...將圖像移動到圓上適當的點。這裏有一些簡單的數學：

編輯：添加了一些評論，並修復了象限錯誤。

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { 
    [super touchesMoved:touches withEvent:event]; 

    CGPoint viewCenter = CGPointMake(self.frame.size.width/2, self.frame.size.height/2); 
    CGPoint imageOrigin = self.imageOnCircle.frame.origin; 
    CGSize imageSize = self.imageOnCircle.frame.size; 
    CGPoint imageCenter = CGPointMake(imageOrigin.x + imageSize.width/2, 
             imageOrigin.y + imageSize.height/2); 

    CGFloat xDist = imageCenter.x - viewCenter.x; 
    CGFloat yDist = imageCenter.y - viewCenter.y; 
    CGFloat radius = sqrt(xDist*xDist + yDist*yDist); 

    CGPoint touchPoint = [[touches anyObject] locationInView:self]; 
    CGFloat touchXDist = touchPoint.x - viewCenter.x; 
    CGFloat touchYDist = touchPoint.y - viewCenter.y; 

    // angles in the view coordinates are measured from the positive x axis 
    // positive value means clockwise rotation 
    // -π/2 is vertically upward (towards the status bar) 
    // π/2 is vertically downward (towards the home button) 

    CGFloat newAngle = atanf(touchYDist/touchXDist); 
    // arctan takes a value between -π/2 and π/2 

    CGFloat newXDist = radius * cosf(newAngle); 
    // cos has a value between -1 and 1 
    // since the angle is between -π/2 and π/2, newXDist will always be positive. 
    if (touchXDist < 0) 
     newXDist *= -1; 

    CGFloat newYDist = radius * sinf(newAngle); 
    // sin has a value between -1 and 1 
    // since the angle is between -π/2 and π/2, newYDist can attain all its values. 
    // however, the sign will be flipped when x is negative. 
    if (touchXDist < 0) 
     newYDist *= -1; 

    CGPoint newCenter = CGPointMake(viewCenter.x + newXDist, 
            viewCenter.y + newYDist); 
    CGPoint newOrigin = CGPointMake(newCenter.x - self.imageOnCircle.frame.size.width/2, 
            newCenter.y - self.imageOnCircle.frame.size.height/2); 
    self.imageOnCircle.frame = CGRectMake(newOrigin.x, 
              newOrigin.y, 
              self.imageOnCircle.frame.size.width, 
              self.imageOnCircle.frame.size.height); 
} 

此外，您可能想添加一個最大/最小角度，以運動限制一方或另一方...