iOS UIImageJPEGRepresentation错误：不是JPEG文件：以0xff 0xd9开头 [英] iOS UIImageJPEGRepresentation error: Not a JPEG file: starts with 0xff 0xd9

问题描述

我正在将.jpg文件写入我的应用文档目录，如下所示：

I am writing a .jpg file to my app's Documents directory like this:

NSData *img = UIImageJPEGRepresentation(myUIImage, 1.0);
BOOL retValue = [img writeToFile:myFilePath atomically:YES];

稍后，我使用以下方法将该图像加载回UIImage：

Later, I load that image back into a UIImage using:

UIImage *myImage = [UIImage imageWithContentsOfFile:path];

我知道它有效，因为我可以在表格单元格中绘制图像，这很好。现在，如果我尝试使用UIImageJPEGRepresentation（myImage，1.0），调试器将打印出这些行：

I know it works because I can draw the image in a table cell and it is fine. Now if I try to use UIImageJPEGRepresentation(myImage, 1.0), the debugger prints out these lines:

<Error>: Not a JPEG file: starts with 0xff 0xd9
<Error>: Application transferred too few scanlines

并且函数返回nil。有人知道为什么会这样吗？加载后我没有做任何事情来操纵UIImage数据。我刚刚将UIImage提供给单元格中的图像视图。我设置了图像视图属性，使得单元格中的所有图像对齐并且大小相同，但我认为这与将UIImage转换为NSData无关。

And the function returns nil. Does anybody have an idea why this would happen? I haven't done anything to manipulate the UIImage data after it was loaded. I just provided the UIImage to an image view in a cell. I set the image view properties such that all the images in the cells line up and are the same size, but I don't think that should have anything to do with being able to convert the UIImage to NSData.

推荐答案

图像没有损坏，我能够正确显示它们。问题可能是UIImage中的一个错误，或者文档应该更清楚使用imageWithContentsOfFile：。

The images were not corrupt, I was able to display them correctly. The issue is possibly a bug in UIImage, or perhaps the documentation should be more clear about using imageWithContentsOfFile:.

我能够通过更改

I was able to eliminate the error message by changing

UIImage *myImage = [UIImage imageWithContentsOfFile:path];

到

NSData *img = [NSData dataWithContentsOfFile:path];
UIImage *photo = [UIImage imageWithData:img];

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