如何确定滚动视图中当前可见的区域并确定中心? [英] How can I determine the area currently visible in a scrollview and determine the center?

问题描述

我有一个地图应用程序，用户可以在其中手动放置航点.我希望他们按下航点按钮，并将航点放置在内容视图上当前可见视图的中心.

I have a map app where the user can place waypoints manually. I would like for them to press the waypoint button and have a waypoint placed in the center of their currently visible view on the content view.

推荐答案

需要考虑缩放的程度，然后可以将内容偏移量转换为完整图像的大小并添加一些内容.///这是地图图像的完整大小CGSize fullSize = CGPointMake(13900，8400);

Need to account for how zoomed it is, then I can convert the content offset to the size of the full image and add some. /// this is the full size of the map image CGSize fullSize = CGPointMake(13900, 8400);

    /// determines how the current content size compares to the full size
    float zoomFactor = size.width/self.contentSize.width; 

    /// apply the zoom factor to the content offset , this basically upscales 
    /// the content offset to apply to the dimensions of the full size map

    float newContentOffsetX = self.contentOffset.x*zoomFactor + (self.bounds.size.width/2) *zoomFactor-300;
    float newContentOffsetY = self.contentOffset.y*zoomFactor + (self.bounds.size.height/2) * zoomFactor-300;

    /// not sure why i needed to subtract the 300, but the formula wasn't putting 
    /// the point in the exact center, subtracting 300 put it there in all situations though 

    CGPoint point = CGPointMake(newContentOffsetX,newContentOffsetY );

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