Helpex - Trao đổi & giúp đỡ Đăng nhập

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.

16 hữu ích 3 bình luận 16k xem chia sẻ

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.

26 hữu ích 0 bình luận chia sẻ

You can use

 if ([UIImage imageWithData:yourNSData]) {
     // there was an image
4 hữu ích 0 bình luận chia sẻ

For Swift try this,

if let image = UIImage(data: yourNSData){
   YourImageView.image = image
4 hữu ích 0 bình luận chia sẻ

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
            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).

3 hữu ích 1 bình luận chia sẻ

In Swift 4.2

self.userImageView.image = UIImage(data: data) != nil ? UIImage(data: data) : UIImage.init(named: "YourDesiredImage")
1 hữu ích 0 bình luận chia sẻ

Give this a try...

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


Nothing worked in my case besides this.

0 hữu ích 0 bình luận chia sẻ
if (tdata !=(NSData *)nil){ 
-1 hữu ích 0 bình luận chia sẻ
if (tdata !=nil){ 

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

-2 hữu ích 0 bình luận chia sẻ
Không tìm thấy câu trả lời bạn tìm kiếm? Duyệt qua các câu hỏi được gắn thẻ ios objective-c iphone uiimageview uiimage , hoặc hỏi câu hỏi của bạn.

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