MKMapView的visibleMapRect属性的奇怪行为 [英] Strange behavior of MKMapView visibleMapRect property

问题描述

我试图设置 visibleMapRect 属性MKMapView对象，但结果映射rect不是我想要的确切。

这是我的代码：

  NSLog（@current size％f％f，mapView.visibleMapRect.size.width ，mapView.visibleMapRect.size.height）; 
 NSLog（@target size％f％f，newBounds.size.width，newBounds.size.height）; 
 mapView.visibleMapRect = newBounds; 
 NSLog（@new size％f％f，mapView.visibleMapRect.size.width，mapView.visibleMapRect.size.height）; 
  

这是结果：

  2013-01-15 19：21：25.440 MyApp [4216：14c03]当前大小67108864.594672 46006272.643333 
 2013-01-15 19：21：25.441 MyApp [4216：14c03] size 3066685.527175 2102356.690531 
 2013-01-15 19：21：25.442 MyApp [4216：14c03] new size 4194304.162631 2875392.126220 
  

这是什么样的魔法？

解决方案

感谢Anna Karenina的评论，我发现了答案。 MKMapView setVisibleMapRect方法显示具有最大缩放级别的矩形以适合输入矩形，并显示地图瓦片每个像素的像素以保持图像看起来清晰。因此，我编写此代码以预测MKMapRect将显示输入MKMapRect。

   - （MKMapRect）expectedMapRectForMapRect：（MKMapRect）mapRect inMapView：（MKMapView *）mapView 
 {
 CGFloat targetPointPerPixelRatio = MAX（MKMapRectGetWidth（mapRect）/ CGRectGetWidth（mapView.bounds），MKMapRectGetHeight（mapRect）/ CGRectGetHeight（mapView.bounds））; 
 CGFloat expextedPointPerPixelRatio = powf（2，ceilf（log2f（targetPointPerPixelRatio）））; 
 
 NSLog（@expextedPointPerPixelRatio％f，expextedPointPerPixelRatio）; 
 MKMapRect expectedMapRect; 
 expectedMapRect.size = MKMapSizeMake（CGRectGetWidth（mapView.bounds）* expextedPointPerPixelRatio，CGRectGetHeight（mapView.bounds）* expextedPointPerPixelRatio）; 
 expectedMapRect.origin = MKMapPointMake（MKMapRectGetMidX（mapRect） -  expectedMapRect.size.width / 2，MKMapRectGetMidY（mapRect） -  expectedMapRect.size.height / 2）; 
 
 expectedMapRect.origin.x = roundf（expectedMapRect.origin.x / expextedPointPerPixelRatio）* expextedPointPerPixelRatio; 
 expectedMapRect.origin.y = roundf（expectedMapRect.origin.y / expextedPointPerPixelRatio）* expextedPointPerPixelRatio; 
 return expectedMapRect; 
} 
  

I tried to set visibleMapRect property of MKMapView object but result map rect is not the exact what I expected.

This is my code:

NSLog(@"current size %f %f", mapView.visibleMapRect.size.width, mapView.visibleMapRect.size.height);
NSLog(@"target size %f %f", newBounds.size.width, newBounds.size.height);
mapView.visibleMapRect = newBounds;
NSLog(@"new size %f %f", mapView.visibleMapRect.size.width, mapView.visibleMapRect.size.height);

And this is the result:

2013-01-15 19:21:25.440 MyApp[4216:14c03] current size 67108864.594672 46006272.643333
2013-01-15 19:21:25.441 MyApp[4216:14c03] target size 3066685.527175 2102356.690531
2013-01-15 19:21:25.442 MyApp[4216:14c03] new size 4194304.162631  2875392.126220

What kind of magic is this? And how can I set the precise visible rect to my map view?

解决方案

Thanks to Anna Karenina's comment I found the answer. MKMapView setVisibleMapRect methods shows rect with maximum zoom level to fit input rect and show map tiles pixel per pixel to keep image looks crisp.

So I write this code to predict MKMapRect that will be shown for input MKMapRect.

- (MKMapRect)expectedMapRectForMapRect:(MKMapRect)mapRect inMapView:(MKMapView*)mapView
{
    CGFloat targetPointPerPixelRatio = MAX(MKMapRectGetWidth(mapRect) / CGRectGetWidth(mapView.bounds), MKMapRectGetHeight(mapRect) / CGRectGetHeight(mapView.bounds));
    CGFloat expextedPointPerPixelRatio = powf(2, ceilf(log2f(targetPointPerPixelRatio)));

    NSLog(@"expextedPointPerPixelRatio %f", expextedPointPerPixelRatio);
    MKMapRect expectedMapRect;
    expectedMapRect.size = MKMapSizeMake(CGRectGetWidth(mapView.bounds)*expextedPointPerPixelRatio, CGRectGetHeight(mapView.bounds)*expextedPointPerPixelRatio);
    expectedMapRect.origin = MKMapPointMake(MKMapRectGetMidX(mapRect) - expectedMapRect.size.width/2, MKMapRectGetMidY(mapRect) - expectedMapRect.size.height/2);

    expectedMapRect.origin.x = roundf(expectedMapRect.origin.x / expextedPointPerPixelRatio) * expextedPointPerPixelRatio;
    expectedMapRect.origin.y = roundf(expectedMapRect.origin.y / expextedPointPerPixelRatio) * expextedPointPerPixelRatio;
    return expectedMapRect;
}

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