NSData to UIImage

user_270635 0
Viewed 61740

I'm trying to save a UIIMage and then retrieve it and display it. I've been successful by saving an image in the bundle, retrieving it from there and displaying. My problem comes from when I try to save an image to disk (converting it to NSData), then retrieving it. I convert the image to NSData like so... 

NSData* topImageData = UIImageJPEGRepresentation(topImage, 1.0);

then I write it to disk like so...

[topImageData writeToFile:topPathToFile atomically:NO];

then I tried to retrieve it like so...

topSubView.image = [[UIImage alloc] initWithContentsOfFile:topPathToFile];

which returns no image (the size is zero). so then I tried...

NSData *data = [[NSData alloc] initWithContentsOfFile:topPathToFile];
topSubView.image = [[UIImage alloc] initWithData:data];

to no avail. When I step through the debugger I do see that data contains the correct number of bytes but I'm confused as to why my image is not being created. Am I missing a step? Do I need to do something with NSData before converting to an image?

nsdata uiimage iphone
5 Answers

You should be able to use class methods of UIImage 

[UIImage imageWithContentsOfFile:topPathToFile];

OR

[UIImage imageWithData:data];

Did that not work?

Hope this helps!

user_833550
user_5993550

Use if-let block with Data to prevent app crash & safe execution of code, as function UIImagePNGRepresentation returns an optional value. 

if let img = UIImage(named: "TestImage.png") {
    if let data:Data = UIImagePNGRepresentation(img) {
       // Handle operations with data here...         
    }
}

Note: Data is Swift 3+ class. Use Data instead of NSData with Swift 3+

Generic image operations (like png & jpg both):

if let img = UIImage(named: "TestImage.png") {  //UIImage(named: "TestImage.jpg")
        if let data:Data = UIImagePNGRepresentation(img) {
               handleOperationWithData(data: data)     
        } else if let data:Data = UIImageJPEGRepresentation(img, 1.0) {
               handleOperationWithData(data: data)     
        }
}

*******
func handleOperationWithData(data: Data) {
     // Handle operations with data here...
     if let image = UIImage(data: data) {
        // Use image...
     }
}

By using extension:

extension UIImage {

    var pngRepresentationData: Data? {
        return UIImagePNGRepresentation(img)
    }

    var jpegRepresentationData: Data? {
        return UIImageJPEGRepresentation(self, 1.0)
    }
}

*******
if let img = UIImage(named: "TestImage.png") {  //UIImage(named: "TestImage.jpg")
      if let data = img.pngRepresentationData {
              handleOperationWithData(data: data)     
      } else if let data = img.jpegRepresentationData {
              handleOperationWithData(data: data)     
     }
}

*******
func handleOperationWithData(data: Data) {
     // Handle operations with data here...
     if let image = UIImage(data: data) {
        // Use image...
     }
}
user_56386300
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