How to check if a NSData is valid for usage in UIImage

问题

NSError *error = nil;
NSURL *url = [NSURL URLWithString:[imageLinks objectAtIndex:0]];
NSData *tdata = [NSData dataWithContentsOfURL:url options:NSDataReadingUncached error:&error];
if (error) {
    NSLog(@"%@", [error localizedDescription]);
}else {
    // no error, this one is being called within my app
    NSLog(@"Data loaded successfully");
}
self.pictureView1.image = [UIImage imageWithData:tdata];

I have a jpeg file, I can confirm that the URL content is gathered successfully, but when I try to put my image data into the UIImage my app fails. I wonder if there is any check for NSData to confirm it is usable for UIImage.

I also don't know what causes this failure, and how to prevent it. Any help would be appreciated.

回答1:

As stated in the documentation imageWithData: returns nil if UIImage could not create an image from the data. The correct way to handle this at runtime is to provide a placeholder image when that method returns nil.

As for the diagnostic, first look at the console messages, they sometimes provide useful info. If not, your best luck is to dump the NSData to disk and compare the result to the file stored on the server. You sometimes get corrupted data, you sometimes just get an html error message where you were expecting jpeg binary data.

回答2:

You can use

 if ([UIImage imageWithData:yourNSData]) {
     // there was an image
 }

回答3:

For Swift try this,

if let image = UIImage(data: yourNSData){
   YourImageView.image = image
}

回答4:

In Swift 4.2

self.userImageView.image = UIImage(data: data) != nil ? UIImage(data: data) : UIImage.init(named: "YourDesiredImage")

回答5:

Give this a try...

if ((dataImage != NULL) && ![v isKindOfClass:[NSNull class]])
{

}

Nothing worked in my case besides this.

回答6:

If you're dealing with a single small image, you could convert Data to an UIImage :

if let _ = UIImage(data: data) {
   print("data contains image data")
} else {
   print("data does not contain image data")
}

But if you're dealing with numerous images or high definition images, you could use what's called The magic bytes in all files, that is, the first few bytes representing a file signature.

Basically you'll just have to extract a few bytes instead of allocation a whole image.

Here is a Data extension using this technique :

import Foundation

extension Data {
    var isImageData: Bool {
        let array = self.withUnsafeBytes {
            [UInt8](UnsafeBufferPointer(start: $0, count: 10))
        }
        let intervals: [[UInt8]] = [
            [0x42, 0x4D], // bmp
            [0xFF, 0xD8, 0xFF], // jpg
            [0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A], // png
            [0x00, 0x00, 0x00, 0x0C, 0x6A, 0x50, 0x20, 0x20], // jpeg2000
            [0x49, 0x49, 0x2A, 0x00], // tiff1
            [0x4D, 0x4D, 0x00, 0x2A] // tiff2
        ]

        for interval in intervals {
            var image = true
            for i in 0..<interval.count {
                if array[i] != interval[i] {
                    image = false
                    break
                }
            }
            if image { return true }
        }
        return false
    }
}

You can add more images or imagine any file type recognition based on that code and file types (see Wikipedia list of file signatures for example).

回答7:

if (tdata !=(NSData *)nil){ 
    NSlog(@"Valid");
}

回答8:

if (tdata !=nil){ 
    NSlog(@"Valid");
}

try this, this would check whether nsdata is empty or not.

来源：https://stackoverflow.com/questions/11072613/how-to-check-if-a-nsdata-is-valid-for-usage-in-uiimage

标签

ios

objective-c

iphone

uiimageview

uiimage