ALAsset和ALAssetRepresentation详解

码客说

发布于 2019-10-22 14:31:42

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发布于 2019-10-22 14:31:42

文章被收录于专栏：码客码客码客

前言

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。

根据URL获取ALAsset

怎样根据url获取ALAsset对象 url类似于(assets-library://asset/asset.PNG?id=2EAEEF99-2C75-4484-B922-9A2F34507537&ext=PNG)

注意这里有个坑在ios8.1上会出现

解决方法如下

定义Block

typedef void(^ZJGetALAssetBlock)(ALAsset *);

获取方法

+ (void)getALAssetByNSURL:(NSURL *)url callback:(ZJGetALAssetBlock)block{
    ALAssetsLibrary *lib = [DNAsset defaultAssetsLibrary];
    [lib assetForURL:url resultBlock:^(ALAsset *asset){
        if (asset) {
            block(asset);
        } else {
            // On iOS 8.1 [library assetForUrl] Photo Streams always returns nil. Try to obtain it in an alternative way
            [lib enumerateGroupsWithTypes:ALAssetsGroupPhotoStream
                               usingBlock:^(ALAssetsGroup *group, BOOL *stop)
             {
                 [group enumerateAssetsWithOptions:NSEnumerationReverse
                                        usingBlock:^(ALAsset *result, NSUInteger index, BOOL *stop) {
                                            
                                            if([[result valueForProperty:ALAssetPropertyAssetURL] isEqual:url])
                                            {
                                                block(asset);
                                                *stop = YES;
                                            }
                                        }];
             }
                             failureBlock:^(NSError *error)
             {
                 block(nil);
             }];
        }
        
    } failureBlock:^(NSError *error){
        block(nil);
    }];
}

属性获取

//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]);

判断选择的是图片还是视频

let representation =  alasset.defaultRepresentation()
//类型
let alassetType = alasset.valueForProperty(ALAssetPropertyType) as! String;
//文件名
let fileName = representation.filename();
//文件大小
let fileSize = representation.size();
//时间
let fileDate = alasset.valueForProperty(ALAssetPropertyDate) as! NSDate;
if(alassetType == ALAssetTypePhoto){
    
}else if(alassetType == ALAssetTypeVideo){
    
}

文件上传

ALAsset的url没法用于上传，虽然可以夺取NSData 但是这样就把数据都加载在内存中，如果是一个较大的视频文件显然是不太合理的所以我们可以把文件自己保存到临时的位置进行上传

定义宏

// 照片原图路径
#define ZJImageCachesPath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"images"]

// 视频URL路径
#define ZJVideoCachesPath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:@"video"]

定义Block

typedef void(^ALAssetToNSURLBlock)(NSURL *);

方法

// 将原始图片转化为NSData数据,写入沙盒
+ (void)getImageUrlWithALAsset:(ALAsset *)asset callback:(ALAssetToNSURLBlock) block
{
    // 创建存放原始图的文件夹--->OriginalPhotoImages
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSFileManager * fileManager = [NSFileManager defaultManager];
        if (![fileManager fileExistsAtPath:ZJImageCachesPath]) {
            [fileManager createDirectoryAtPath:ZJImageCachesPath withIntermediateDirectories:YES attributes:nil error:nil];
        }
        
        ALAssetRepresentation *rep = [asset defaultRepresentation];
        Byte *buffer = (Byte*)malloc((unsigned long)rep.size);
        NSUInteger buffered = [rep getBytes:buffer fromOffset:0.0 length:((unsigned long)rep.size) error:nil];
        NSData *data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];
        NSString * imagePath = [ZJImageCachesPath stringByAppendingPathComponent:rep.filename];
        //删除原有的临时文件
        if ([fileManager fileExistsAtPath:imagePath]) {
            [fileManager removeItemAtPath:imagePath error:nil];
        }
        [data writeToFile:imagePath atomically:YES];
        block([NSURL fileURLWithPath:imagePath]);
    });
}

// 将原始视频转化为NSData数据,写入沙盒
+ (void)getVideoUrlWithALAsset:(ALAsset *)asset callback:(ALAssetToNSURLBlock) block
{
    // 解析一下,为什么视频不像图片一样一次性开辟本身大小的内存写入?
    // 想想,如果1个视频有1G多,难道直接开辟1G多的空间大小来写?
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSFileManager * fileManager = [NSFileManager defaultManager];
        if (![fileManager fileExistsAtPath:ZJVideoCachesPath]) {
            [fileManager createDirectoryAtPath:ZJVideoCachesPath withIntermediateDirectories:YES attributes:nil error:nil];
        }
        
        ALAssetRepresentation *rep = [asset defaultRepresentation];
        NSString * videoPath = [ZJVideoCachesPath stringByAppendingPathComponent:rep.filename];
        
        //删除原有的临时文件
        if ([fileManager fileExistsAtPath:videoPath]) {
            [fileManager removeItemAtPath:videoPath error:nil];
        }
        char const *cvideoPath = [videoPath UTF8String];
        FILE *file = fopen(cvideoPath, "ab+");
        if (file) {
            const int bufferSize = 1024 * 1024;
            // 初始化一个1M的buffer
            Byte *buffer = (Byte*)malloc(bufferSize);
            NSUInteger read = 0, offset = 0, written = 0;
            NSError* err = nil;
            if (rep.size != 0)
            {
                do {
                    read = [rep getBytes:buffer fromOffset:offset length:bufferSize error:&err];
                    written = fwrite(buffer, sizeof(char), read, file);
                    offset += read;
                } while (read != 0 && !err);//没到结尾，没出错，ok继续
            }
            // 释放缓冲区，关闭文件
            free(buffer);
            buffer = NULL;
            fclose(file);
            file = NULL;
        }
        block([NSURL fileURLWithPath:videoPath]);
    });
}

用Alamofire上传

上传时附带其他参数(multipart) 但是这种方式没法得到上传进度

//上传文件
static func uploadImage(url:String,parameters:[String:AnyObject],imagePath:NSURL,fileParName:String){
Alamofire.upload(
    .POST,
    url,
    multipartFormData: { multipartFormData in
        multipartFormData.appendBodyPart(fileURL: imagePath, name: fileParName)
        // 这里就是绑定参数的地方
        for (key, value) in parameters {
            if(value.stringValue != nil){
                multipartFormData.appendBodyPart(data: value.stringValue.dataUsingEncoding(NSUTF8StringEncoding)!, name: key);
            }
        }
    },
    encodingCompletion: { encodingResult in
        switch encodingResult {
        case .Success(let upload, _, _):
            upload.responseJSON { response in
                debugPrint(response)
            }
        case .Failure(let encodingError):
            print(encodingError)
        }
    }
)

可以获取上传进度的方式但是没法附带其他参数

Alamofire.upload(.POST, "https://httpbin.org/post", file: imagePath)
    .progress { bytesWritten, totalBytesWritten, totalBytesExpectedToWrite in
        dispatch_async(dispatch_get_main_queue()) {
            print("Total bytes written on main queue: \(totalBytesWritten)")
        }
    }
    .validate()
    .responseJSON { response in
        debugPrint(response)
}

所以例如设置用户头像等就用第一种方式要是做文件上传就必须用第二种方式第二种方式也能控制暂停、继续、停止等操作

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原始发表：2016-06-03，如有侵权请联系 cloudcommunity@tencent.com 删除

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