ALAsset和ALAssetRepresentation详解

ALAsset类代表相册中的每个资源文件，可以通过它获取资源文件的相关信息还能修改和新建资源文件，ALAssetRepresentation类代表相册中每个资源文件的详细信息，可以通过它获取资源的大小，名字，路径等详细信息。

//通过ALAsset获取相对应的资源，获取图片的等比缩略图，原图的等比缩略

                        CGImageRef ratioThum = [asset aspectRatioThumbnail];

                        //获取相片的缩略图，该缩略图是相册中每张照片的poster图

                        CGImageRef thum = [asset thumbnail];

                        UIImage* rti = [UIImage imageWithCGImage:ratioThum];

                        UIImage* ti = [UIImage imageWithCGImage:thum];

                        UIImageView* v1 = [[UIImageView alloc]initWithFrame:CGRectMake(20, 100, 120, 200)];

                        v1.image = rti;

                        v1.contentMode = UIViewContentModeScaleAspectFit;

                        UIImageView* v2 = [[UIImageView alloc]initWithFrame:CGRectMake(180, 100, 120, 200)];

                        v2.image = ti;

                        v2.contentMode = UIViewContentModeScaleAspectFit;

                        [self.view addSubview:v1];

                        [self.view addSubview:v2];

左侧为等比缩略图效果，右侧为poster效果的缩略图

UIImage* ni = [UIImage imageNamed:@"new.png"];

                        //修改指定路径的图片资源内容，替换掉原来的内容

                        [asset setImageData:UIImageJPEGRepresentation(ni, 1.0) metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {

                            NSLog(@"new:%@",assetURL);

                        }];

                        //根据给定的图片内容，重新生成一张新图

                        [asset writeModifiedImageDataToSavedPhotosAlbum:UIImageJPEGRepresentation(ni, 1.0) metadata:nil completionBlock:^(NSURL *assetURL, NSError *error) {

                            NSLog(@"new:%@",assetURL);

                        }];

                        //获取资源图片的详细资源信息

                        ALAssetRepresentation* representation = [asset defaultRepresentation];

                        //获取资源图片的长宽

                        CGSize dimension = [representation dimensions];

                        //获取资源图片的高清图

                        [representation fullResolutionImage];

                        //获取资源图片的全屏图

                        [representation fullScreenImage];

                        //获取资源图片的名字

                        NSString* filename = [representation filename];

                        NSLog(@"filename:%@",filename);

                        //缩放倍数

                        [representation scale];

                        //图片资源容量大小

                        [representation size];

                        //图片资源原数据

                        [representation metadata];

                        //旋转方向

                        [representation orientation];

                        //资源图片url地址，该地址和ALAsset通过ALAssetPropertyAssetURL获取的url地址是一样的

                        NSURL* url = [representation url];

                        NSLog(@"url:%@",url);

                        //资源图片uti，唯一标示符

                        NSLog(@"uti:%@",[representation UTI]);