Objective c 读取同一文件时无法获取保存的数据字节

我正在使用writeToFile和下面的代码将NSMutableData写入图像文件

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *file = [documentsDirectory stringByAppendingPathComponent:@"binaryData.jpg"];
NSMutableData *data = [NSMutableData alloc];
[data appendData:rawData]; 
[data writeToFile:file atomically:NO];

NSLog (@"Data Length: %d.",data.length); 

// Data Length: 30506

-(void)imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info
{
    UIImage *selectedImageFile = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData *PNGData = [NSData dataWithData:UIImagePNGRepresentation(selectedImageFile)];
    NSData *JPEGData = [NSData dataWithData:UIImageJPEGRepresentation(selectedImageFile, 1.0)];

    NSURL *imageURL = [info objectForKey:UIImagePickerControllerReferenceURL];
    ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];

    [library assetForURL:imageURL resultBlock:^(ALAsset *asset) {

        Byte *buffer = (Byte*)malloc(asset.defaultRepresentation.size);
        NSUInteger k = [asset.defaultRepresentation getBytes:buffer fromOffset: 0.0 length:asset.defaultRepresentation.size error:nil];
        rawData = [NSData dataWithBytesNoCopy:buffer length:k freeWhenDone:YES];  

    }

    NSLog (@"PNG Length: %d.", PNGData.length); // PNG Length: 78101
    NSLog (@"JPEG Length: %d.", JPEGData.length); // JPEG Length: 37548
    NSLog (@"Raw Data Length: %d.", PNGData.length); // Raw Data Length: 34163


}

我正在用下面的代码读取保存的图像文件

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *file = [documentsDirectory stringByAppendingPathComponent:@"binaryData.jpg"];
NSMutableData *data = [NSMutableData alloc];
[data appendData:rawData]; 
[data writeToFile:file atomically:NO];

NSLog (@"Data Length: %d.",data.length); 

// Data Length: 30506

-(void)imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info
{
    UIImage *selectedImageFile = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData *PNGData = [NSData dataWithData:UIImagePNGRepresentation(selectedImageFile)];
    NSData *JPEGData = [NSData dataWithData:UIImageJPEGRepresentation(selectedImageFile, 1.0)];

    NSURL *imageURL = [info objectForKey:UIImagePickerControllerReferenceURL];
    ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];

    [library assetForURL:imageURL resultBlock:^(ALAsset *asset) {

        Byte *buffer = (Byte*)malloc(asset.defaultRepresentation.size);
        NSUInteger k = [asset.defaultRepresentation getBytes:buffer fromOffset: 0.0 length:asset.defaultRepresentation.size error:nil];
        rawData = [NSData dataWithBytesNoCopy:buffer length:k freeWhenDone:YES];  

    }

    NSLog (@"PNG Length: %d.", PNGData.length); // PNG Length: 78101
    NSLog (@"JPEG Length: %d.", JPEGData.length); // JPEG Length: 37548
    NSLog (@"Raw Data Length: %d.", PNGData.length); // Raw Data Length: 34163


}

如果您看到上面的代码，我的源数据长度为“30506”，然后发送到WriteFile

但我无法在使用UIImagePickerController读取相同图像时获得相同的字节

我试过使用UIImagePNGRepresentation、uiimagejpegresentation和ALAssetsLibrary。但在我的任何试验中，我都无法获得相同的字节

---

有人能告诉我如何保存/获取相同的字节吗？

这看起来很棘手：

[NSMutableData alloc]。添加
init
调用，看看它是否有什么不同。但是，既然您已经将数据作为
NSData
对象（
[data appendData:rawData]；
），为什么还要创建
NSMutableData
）？稍后我将附加更多的NSData对象。这就是我声明NSMutableData的原因。我试过你的选择，但没有区别。