Iphone 从触摸视图的点拖动视图

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;

    }


}

但是我想从我接触它的地方开始拖动视图或图像。例如，如果我拖动（我高亮显示视图并将蓝色放置在光标上）：

当我开始拖动时，如果我向右拖动鼠标20 px，那么我希望视图也拖动20 px，而不是：

也许我得把视角的中心换到我第一次碰到它的地方。我怎么能这么做

换句话说，当你在iPad上拖动应用程序时，我想做一些类似的事情：

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;
    }
}

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确保定位。y-星形以及东西的x侧是正确的。我忘了提到这个例子只是沿着x轴拖动一些东西。确保做location.y-startY以及东西的x面都是正确的。我忘了提到这个例子只是沿着x轴拖动一些东西。