現(xiàn)象描述

圖片在相冊中的顯示方向是對的嫂用，但是從相冊中取出圖片然后顯示在UIImageView上時圖片發(fā)生了旋轉(zhuǎn)型凳；

使用下面的取圖片方法圖片會發(fā)生旋轉(zhuǎn)

用下面這段代碼取出圖片在放到UIImageView上就可能會發(fā)生旋轉(zhuǎn)

// 通過ALAsset獲取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;
}

// 通過assetURL獲取ALAsset
- (void)assetFromURL:(NSURL*)assetsUrl
{
    ALAssetsLibrary *lib = [[ALAssetsLibrary alloc] init];
    [lib assetForURL:assetsUrl resultBlock:^(ALAsset *asset) {
        // _OrientationIV是UIImageView的一個實例
        _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];
}

但是同一張圖片用下面的代碼獲取就不會發(fā)生旋轉(zhuǎn)

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary<NSString *,id> *)info
{    UIImage *img = [info objectForKey:UIImagePickerControllerOriginalImage];
    _OrientationIV.image = img;  // _OrientationIV是UIImageView的一個實例
    [picker dismissViewControllerAnimated:YES completion:nil];
}

所以猜測發(fā)生旋轉(zhuǎn)的問題可能發(fā)生在通過ALAsset獲取UIImage這塊代碼中的下面這一行代碼

// 方法一
UIImage *img = [[UIImage alloc]initWithCGImage:ref ];

于是查看API文檔，發(fā)現(xiàn)還有一個通過CGImage生成UIImage的方法

// 方法二
- (instancetype)initWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation

這個“方法二”比“方法一”多了一個scale參數(shù)和一個orientation參數(shù),這里要使用orientation參數(shù)來解決問題嘱函；

恰好ALAssetRepresentation中有一個獲取orientation的方法甘畅，只要將orientation做參數(shù)傳遞給“方法二”就可以解決圖片旋轉(zhuǎn)的問題，

這里有一個注意點."方法二"中參數(shù)的類型是UIImageOrientation類型往弓，而從ALAssetRepresentation中獲取的orientation是ALAssetOrientation類型疏唾，所以在使用時要用下面的代碼做一下強(qiáng)轉(zhuǎn)

UIImageOrientation orientation = (UIImageOrientation)[rep orientation];

最終正確的代碼如下：

- (UIImage *) imageFromALAsset:(ALAsset *)asset
{
    if ([[asset valueForProperty:ALAssetPropertyType] isEqualToString:ALAssetTypePhoto])
    {
        ALAssetRepresentation *rep = [asset defaultRepresentation];
        CGImageRef ref = [rep fullResolutionImage];
        // 解決圖片發(fā)生旋轉(zhuǎn)的問題
        UIImageOrientation orientation = (UIImageOrientation)[rep orientation];
        UIImage *img = [[UIImage alloc]initWithCGImage:ref scale:1.0 orientation:orientation];
        return img;
    }
    return nil;
}

知識點

• imageOrientation