现象描述
图片在相册中的显示方向是对的,但是从相册中取出图片然后显示在UIImageView上时图片发生了旋转;
使用下面的取图片方法图片会发生旋转
用下面这段代码取出图片在放到UIImageView上就可能会发生旋转
// 通过ALAsset获取UIImage
- (UIImage *) imageFromALAsset:(ALAsset *)asset
{
if ([[asset valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])
{
ALAssetRepresentation *rep = [asset defaultRepresentation];
CGImageRef ref = [rep fullResolutionImage];
UIImage *img = [[UIImage alloc]initWithCGImage:ref ];
return img;
}
return nil;
}
// 通过assetURL获取ALAsset
- (void)assetFromURL:(NSURL*)assetsUrl
{
ALAssetsLibrary *lib = [[ALAssetsLibrary alloc] init];
[lib assetForURL:assetsUrl resultBlock:^(ALAsset *asset) {
// _OrientationIV是UIImageView的一个实例
_OrientationIV.image = [self imageFromALAsset:asset];
} failureBlock:^(NSError *error) {
}];
}
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{
NSURL *as = [info objectForKey:UIImagePickerControllerReferenceURL];
[self assetFromURL:as];
[picker dismissViewControllerAnimated:YES completion:nil];
}
但是同一张图片用下面的代码获取就不会发生旋转
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{ UIImage *img = [info objectForKey:UIImagePickerControllerOriginalImage];
_OrientationIV.image = img; // _OrientationIV是UIImageView的一个实例
[picker dismissViewControllerAnimated:YES completion:nil];
}
所以猜测发生旋转的问题可能发生在通过ALAsset获取UIImage这块代码中的下面这一行代码
// 方法一
UIImage *img = [[UIImage alloc]initWithCGImage:ref ];
于是查看API文档,发现还有一个通过CGImage生成UIImage的方法
// 方法二
- (instancetype)initWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation
这个“方法二”比“方法一”多了一个scale
参数和一个orientation
参数,这里要使用orientation
参数来解决问题;
恰好ALAssetRepresentation
中有一个获取orientation
的方法,只要将orientation
做参数传递给“方法二”就可以解决图片旋转的问题,
这里有一个注意点."方法二"中参数的类型是
UIImageOrientation
类型,而从ALAssetRepresentation
中获取的orientation
是ALAssetOrientation
类型,所以在使用时要用下面的代码做一下强转
UIImageOrientation orientation = (UIImageOrientation)[rep orientation];
最终正确的代码如下:
- (UIImage *) imageFromALAsset:(ALAsset *)asset
{
if ([[asset valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])
{
ALAssetRepresentation *rep = [asset defaultRepresentation];
CGImageRef ref = [rep fullResolutionImage];
// 解决图片发生旋转的问题
UIImageOrientation orientation = (UIImageOrientation)[rep orientation];
UIImage *img = [[UIImage alloc]initWithCGImage:ref scale:1.0 orientation:orientation];
return img;
}
return nil;
}
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