如何在 Objective-C 中将 PHAsset 转换为 UIImage

Question

我有一个充满PHAsset 对象（https://developer.apple.com/library/prerelease/ios/documentation/Photos/Reference/PHAsset_Class/index.html）的数组，我想知道如何将它们转换为 UIImage，然后将它们保存在数组中。

包含 PHAsset 对象的数组称为 self.assets，这是我目前所拥有的：

PHImageManager *manager = [PHImageManager defaultManager];

CGFloat scale = UIScreen.mainScreen.scale;

NSMutableArray *images = [NSMutableArray arrayWithCapacity:[self.assets count]];

for (int i = 0; i < [self.assets count]; i++) {

    CGSize targetSize = CGSizeMake(scale, scale);

    [manager requestImageForAsset:[self.assets objectAtIndex:i]
                       targetSize:targetSize
                      contentMode:PHImageContentModeAspectFill
                          options:self.requestOptions
                    resultHandler:^(UIImage *image, NSDictionary *info){
                        [images addObject:image];
                    }];
}

self.requestOptions 是 .h 中的一个属性

@property (nonatomic, strong) PHImageRequestOptions *requestOptions;

在 viewDidLoad 我正在这样做：

self.requestOptions = [[PHImageRequestOptions alloc] init];
self.requestOptions.resizeMode   = PHImageRequestOptionsResizeModeExact;
self.requestOptions.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;

但在进行一些调试后，我一直看到self.assets 具有以下值：

(
<PHAsset: 0x1743828a0> 3B6D658D-EC76-43A1-9793-35D889E9CF15/L0/001 mediaType=1/0, assetSource=3, (2448x2448), creationDate=2015-07-27 02:02:46 +0000, location=1, hidden=0, favorite=0 ,
<PHAsset: 0x174382970> 50F05575-71D2-446B-BD1E-8E3250E375AD/L0/001 mediaType=1/0, assetSource=3, (2448x2448), creationDate=2015-07-27 02:02:47 +0000, location=1, hidden=0, favorite=0 
)

而images 为空。有谁知道我如何将 PHAssets 添加到 UIImages 并将它们添加到 images 数组中？任何帮助表示赞赏。谢谢！

Answer 1

对于任何像我一样在这个问题上苦苦挣扎的人，这是要走的路。

首先将requestOptions设置为：

self.requestOptions = [[PHImageRequestOptions alloc] init];
self.requestOptions.resizeMode   = PHImageRequestOptionsResizeModeExact;
self.requestOptions.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;

// this one is key
self.requestOptions.synchronous = YES;

如果在一个填充有 PHAsset 对象的数组中有多个资产，则添加以下代码：

self.assets = [NSMutableArray arrayWithArray:assets];
PHImageManager *manager = [PHImageManager defaultManager];
NSMutableArray *images = [NSMutableArray arrayWithCapacity:[assets count]];

// assets contains PHAsset objects.
 __block UIImage *ima;

for (PHAsset *asset in self.assets) {
    // Do something with the asset

    [manager requestImageForAsset:asset
                       targetSize:PHImageManagerMaximumSize
                      contentMode:PHImageContentModeDefault
                          options:self.requestOptions
                    resultHandler:^void(UIImage *image, NSDictionary *info) {
                        ima = image;

                        [images addObject:ima];
                    }];


}

现在images 数组包含uiimage 格式的所有图像。

Answer 2

Swift 3.0 答案

let photoAsset = asset
        let manager = PHImageManager.default()
        var options: PHImageRequestOptions?
        options = PHImageRequestOptions()
        options?.resizeMode = .exact
        options?.isSynchronous = true
        manager.requestImage(
            for: photoAsset,
            targetSize: PHImageManagerMaximumSize,
            contentMode: .aspectFill,
            options: options
        ) { [weak self] result, _ in
            completion(result)
        }

options?.isSynchronous = true很重要

BOOL synchronous; // return only a single result, blocking until available (or failure). Defaults to NO

Answer 3

图像可能为零（很少）。最好评估一下，否则array add nil会导致app崩溃。

if(image){
    ima = image;
    [images addObject:ima];
}