从您触摸iPhone的点拖动视图

Question

我知道如何拖动视图或对象：

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

    UITouch *touch = [[event allTouches] anyObject];


    if( [touch view] == ViewMain)
    {
       CGPoint location = [touch locationInView:self.view];
       ViewMain.center = location;

    }


}

但我想从触摸它的位置开始拖动该视图或图像。例如，如果我拖动（我突出显示视图并在光标上放置蓝色）：

我开始拖动的那一刻，如果我将鼠标向右拖动20 px然后我希望视图也拖动20 px而不是：

也许我必须将视图的中心更改为我触摸它的位置。我怎么能这样做？

换句话说，我想做的事情就像在iPad上拖动应用程序时那样：

Answer 1

float startX = 0;
float startY = 0;
-(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event allTouches] anyObject];

    if( [touch view] == ViewMain)
    {
        CGPoint location = [touch locationInView:self.view];
        startX = location.x - ViewMain.center.x;        
        startY = ViewMain.center.y;
    }
}
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
    UITouch *touch = [[event allTouches] anyObject];
    if( [touch view] == ViewMain)
    {
        CGPoint location = [touch locationInView:self.view];
        location.x =location.x - startX;
        location.y = startY;
        ViewMain.center = location;
    }
}