Q:
iOS18 發(fā)布之后，收到了很多拉起相冊時的崩潰客訴朴摊。堆棧日志如下：
#0 Thread
NSInternalInconsistencyException
opportunisticDegradedImagesToReturn cannot be zero.
解析原始
0
CoreFoundation
___exceptionPreprocess + 164
6
Photos
-[PHImageManager requestImageForAsset:targetSize:contentMode:options:resultHandler:] + 172
......(略)
crash 位置還是很清晰的默垄，但是原因不清晰啊，沒見過這個報錯甚纲，網(wǎng)上也沒搜到有效信息口锭，也沒聽說 iOS18 后，相冊哪里要做額外的兼容介杆。
我們項目中的這塊代碼實現(xiàn)鹃操，簡略如下：
PHImageRequestOptions *imageRequestOptions = [[PHImageRequestOptions alloc] initWithImageRequestOptions:options];
imageRequestOptions.synchronous = YES;
imageRequestOptions.networkAccessAllowed = YES;
imageRequestOptions.resizeMode = PHImageRequestOptionsResizeModeFast;
imageRequestOptions.deliveryMode = PHImageRequestOptionsDeliveryModeOpportunistic;
[[PHImageManager defaultManager] requestImageForAsset:phAsset targetSize:targetSize contentMode:PHImageContentModeAspectFit options:imageRequestOptions resultHandler:^(UIImage * _Nullable result, NSDictionary * _Nullable info) {
// TODO: image something
}];
A:
從報錯信息看，主要是說 opportunisticDegradedImages 這個東西春哨，不能是 zero荆隘，那 opportunistic 和 degraded 這兩個關鍵詞是什么意思呢？
opportunistic：
指的是 PHImageRequestOptions 對象 deliveryMode 屬性的值悲靴，他表示請求的圖像質(zhì)量和交付優(yōu)先級臭胜。我用的默認值 PHImageRequestOptionsDeliveryModeOpportunistic，表示平衡下圖像質(zhì)量和響應速度癞尚，也就是報錯這個關鍵詞耸三。詳情可參考這篇文章：鏈接
@property (nonatomic, assign) PHImageRequestOptionsDeliveryMode deliveryMode; // delivery mode. Defaults to PHImageRequestOptionsDeliveryModeOpportunistic
typedef NS_ENUM(NSInteger, PHImageRequestOptionsDeliveryMode) {
PHImageRequestOptionsDeliveryModeOpportunistic = 0, // client may get several image results when the call is asynchronous or will get one result when the call is synchronous
PHImageRequestOptionsDeliveryModeHighQualityFormat = 1, // client will get one result only and it will be as asked or better than asked
PHImageRequestOptionsDeliveryModeFastFormat = 2 // client will get one result only and it may be degraded
};
degraded：
這單詞是降級的意思，翻了翻 PHImageRequestOptions 的 API浇揩，allowSecondaryDegradedImage 屬性看起來比較接近仪壮，他表示除了初始的降級結果之外，如果條件允許胳徽，是否還返回一個額外的降級結果积锅。
這是 iOS17 新增的 API爽彤，官方也并沒太多的說明介紹 AppleDevelopDoc鏈接
@property (nonatomic) BOOL allowSecondaryDegradedImage API_AVAILABLE(macos(14), ios(17), tvos(17)); // in addition to the initial degraded result, an additional degraded result will be returned if conditions permit
fix 方案：
于是嘗試把 allowSecondaryDegradedImage 設為 YES 看看，然后就 OK 了缚陷。适篙。。就不崩了箫爷。嚷节。。虎锚。
if (@available(iOS 17, *)) {
imageRequestOptions.allowSecondaryDegradedImage = YES;
} else {
// Fallback on earlier versions
}
至于底層原理是為什么硫痰，我也不清楚，只是根據(jù)報錯信息窜护，蒙著改了效斑。如果有了解這塊的朋友，歡迎大家留言討論柱徙。
