取相册第一张图片--ALAssetsLibrary使用

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转载： http://small.qiang.blog.163.com/blog/static/97849307201402133420155/

ALAssetsLibrary使用

在iOS中，我们调用摄像头和选择相册中的资源，我们可以使用：UIImagePickerController类来完成。

当然，我们也可以不使用UI的形式来访问iOS设备的相册资源。

那就是使用：ALAssetsLibrary

一、ALAssetsLibrary是什么

可以说，是一个桥梁把。连接了我们应用程序和相册之间的访问。

ALAssetsLibrary提供了我们对iOS设备中的相片、视频的访问。

ALAssetsLibrary被封装在框架中。所以，我们在使用时，需要引入该框架。

需添加AssetsLibrary.framework
然后引入

#import <AssetsLibrary/ALAsset.h>

#import <AssetsLibrary/ALAssetsLibrary.h>

#import <AssetsLibrary/ALAssetsGroup.h>

#import <AssetsLibrary/ALAssetRepresentation.h>

self.assetsLibrary= [[ALAssetsLibraryalloc]init];

    dispatch_queue_t dispatchQueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);

    dispatch_async(dispatchQueue, ^(void) {

        // 遍历所有相册

        [self.assetsLibraryenumerateGroupsWithTypes:ALAssetsGroupAll

                                         usingBlock:^(ALAssetsGroup*group, BOOL*stop) {

                                              // 遍历每个相册中的项ALAsset

                                              [groupenumerateAssetsUsingBlock:^(ALAsset*result, NSUIntegerindex,BOOL*stop) {

                                                  __blockBOOLfoundThePhoto = NO;

                                                  if(foundThePhoto){

                                                      *stop = YES;

}

                                                  // ALAsset的类型

                                                  NSString*assetType = [result valueForProperty:ALAssetPropertyType];

                                                  if([assetType isEqualToString:ALAssetTypePhoto]){

                                                      foundThePhoto = YES;

                                                      *stop = YES;

                                                      ALAssetRepresentation*assetRepresentation =[result defaultRepresentation];

                                                      CGFloatimageScale = [assetRepresentation scale];

                                                      UIImageOrientationimageOrientation = (UIImageOrientation)[assetRepresentation orientation];

                                                      dispatch_async(dispatch_get_main_queue(), ^(void) {

                                                          CGImageRefimageReference = [assetRepresentation fullResolutionImage];

                                                          // 对找到的图片进行操作

                                                          UIImage*image =[[UIImagealloc]initWithCGImage:imageReferencescale:imageScaleorientation:imageOrientation];

                                                          if(image != nil){

                                                              //获取到第一张图片

                                                          }else{

                                                              NSLog(@"Failed to create the image.");

                                                          } });

}

}];

}

                                       failureBlock:^(NSError*error) {

                                            NSLog(@"Failed to enumerate the asset groups.");

}];

});

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