读取照片库PhotoLibrary
iOS中如果我们只有一次读取一张图片或者一个视频（或拍一张照片/视频）的需求，那么我们用 UIImagePickerController 就可以搞定。但是很多时候我们需要一次性从PhotoLibrary读取多个照片或者视频，这时候我们就需要另辟蹊径了，好在apple为我们提供了相应的接口。
在开始coding之前我们想要认识几个类：
ALAssetsLibrary：代表整个PhotoLibrary，我们可以生成一个它的实例对象，这个实例对象就相当于是照片库的句柄。
ALAssetsGroup：照片库的分组，我们可以通过ALAssetsLibrary的实例获取所有的分组的句柄。
ALAsset：一个ALAsset的实例代表一个资产，也就是一个photo或者video，我们可以通过他的实例获取对应的subnail或者原图等等。
还需要了解的一个东东就是blocks，apple在iOS 4.0以后大量出现了这玩意儿，有使用越来越广的意思，不过这玩意儿确实好用。关于这玩意儿的内容我在这里不多讲，关注我的博客我会细讲。
对于本文的需求，我们读取group和每个asset都是异步的，但是我们现在用blocks我们可以在一个函数里面搞定。所以blocks确实很方便。
下面直接看代码吧:
ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc]init];//生成整个photolibrary句柄的实例
NSMutableArray *mediaArray = [[NSMutableArray alloc]init];//存放media的数组
[assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {//获取所有group
[group enumerateAssetsUsingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {//从group里面
NSString* assetType = [result valueForProperty:ALAssetPropertyType];
if ([assetType isEqualToString:ALAssetTypePhoto]) {
NSLog(@"Photo");
}else if([assetType isEqualToString:ALAssetTypeVideo]){
NSLog(@"Video");
}else if([assetType isEqualToString:ALAssetTypeUnknown]){
NSLog(@"Unknow AssetType");
}
NSDictionary *assetUrls = [result valueForProperty:ALAssetPropertyURLs];
NSUInteger assetCounter = 0;
for (NSString *assetURLKey in assetUrls) {
NSLog(@"Asset URL %lu = %@",(unsigned long)assetCounter,[assetUrls objectForKey:assetURLKey]);
}
NSLog(@"Representation Size = %lld",[[result defaultRepresentation]size]);
}];
} failureBlock:^(NSError *error) {
NSLog(@"Enumerate the asset groups failed.");
}];
保存图片或视频到PhotoLibrary
时文件然后，然后通过临时文件的路径去转存到photo library。
我们直接来看相应的API：
// These methods can be used to add photos or videos to the saved photos album. // With a UIImage, the API user can use -[UIImage CGImage] to get a CGImageRef, and cast -[UIImage imageOrientation] to ALAssetOrientation. - (void)writeImageToSavedPhotosAlbum:(CGImageRef)imageRef orientation:(ALAssetOrientation)orientation completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock; // The API user will have to specify the orientation key in the metadata dictionary to preserve the orientation of the image - (void)writeImageToSavedPhotosAlbum:(CGImageRef)imageRef metadata:(NSDictionary *)metadata completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_1); // If there is a conflict between the metadata in the image data and the metadata dictionary, the image data metadata values will be overwritten - (void)writeImageDataToSavedPhotosAlbum:(NSData *)imageData metadata:(NSDictionary *)metadata completionBlock:(ALAssetsLibraryWriteImageCompletionBlock)completionBlock __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_1); - (void)writeVideoAtPathToSavedPhotosAlbum:(NSURL *)videoPathURL completionBlock:(ALAssetsLibraryWriteVideoCompletionBlock)completionBlock;
- (void)saveImage:(UIImage*)image{
ALAssetsLibrary *assetsLibrary = [[ALAssetsLibrary alloc]init];
[assetsLibrary writeImageToSavedPhotosAlbum:[image CGImage] orientation:(ALAssetOrientation)image.imageOrientation completionBlock:^(NSURL *assetURL, NSError *error) {
if (error) {
NSLog(@"Save image fail：%@",error);
}else{
NSLog(@"Save image succeed.");
}
}];
}
- (void)save:(NSString*)urlString{
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:urlString]
completionBlock:^(NSURL *assetURL, NSError *error) {
if (error) {
NSLog(@"Save video fail:%@",error);
} else {
NSLog(@"Save video succeed.");
}
}];
}
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