Setting the NSImage of a NSImageView from a NSURL

Question

Okay, so I'm a newbie trying to write a practice app where you click a button, an NSOpenPanel appears, you select an image file, and the image gets displayed in an NSImageView.

I've got the open panel working okay, and it returns an NSArray of NSURLs. I avoided using filename paths as the Apple docs said it was depreciated. I then try to make an NSImage object using initWithContentsOfURL, and then try to setImage of the NSImageView to the new image.

Here's what I think are the relevant parts of the implementation...

   - (IBAction)openImage:(NSButton *)sender {
    NSLog(@"%@ was clicked", sender);

    NSOpenPanel *panel = [[NSOpenPanel alloc] init];

    if ([panel runModal] == NSModalResponseOK)
    {
        NSArray* selectedFile = [panel URLs];
        NSLog(@"%@ was selected", selectedFile[0]);
        NSImage *theImage = [[NSImage alloc] initWithContentsOfURL:selectedFile[0]];

        [imageViewer setImage:theImage];
        }
    }

And from the header:

    @property (weak) IBOutlet NSImageView *imageViewer;
    - (IBAction)openImage:(NSButton *)sender;
   @end

When I try to set the image, Xcode says there's imageViewer is undeclared, and wants to correct it to _imageViewer. I tried following its advice and ran it, but then the app just crashes once I select a file from the open panel so something is obviously still not right.

The NSLog lines shows the button was clicked, and shows the correct URL of the file selected, but I'm having issues setting the NSImageView. It's probably something really simple but I can't seem to figure it out.

Use self.imageViewer or use _imageViewer. I suggest using self.imageViewer as it uses the setter. — Hermann Klecker, May 27 '15 at 07:32

score 1 · Answer 1 · answered May 27 '15 at 07:43

You need to declare the variable imageViewer in your headers (.h) interface , for example:

@interface AppDelegate : NSObject <NSApplicationDelegate> {
     IBOutlet NSImageView *__weak imageViewer; 
}
@property (weak) IBOutlet NSImageView *imageViewer;
- (IBAction)openImage:(NSButton *)sender;
@end

Then in your class (.m) just synthesize the variable:

@implementation AppDelegate
@synthesize imageViewer;

...

Since you hadn't declared the variable in the interface you were receiving the error.

score 0 · Answer 2 · answered May 27 '15 at 07:36

Try this code.

- (IBAction)openImage:(NSButton *)sender {
    NSLog(@"%@ was clicked", sender);

    NSOpenPanel *panel = [[NSOpenPanel alloc] init];

    if ([panel runModal] == NSModalResponseOK)
    {
        NSArray* selectedFile = [panel URLs];
        NSLog(@"%@ was selected", selectedFile[0]);
        NSURL *url = (NSURL *)selectedFile[0];
        NSString *filePath = [url absoluteString];
        NSImage *theImage = [[NSImage alloc] initWithContentsOfFile:filePath];

        [imageViewer setImage:theImage];
        }
    }

score 0 · Accepted Answer · answered May 28 '15 at 01:09

Okay, so I feel stupid now. I'm still learning stuff so I wasn't sure why it was freezing up until I noticed Xcode kept switching to the "Debug" panel, which clued me into what might be happening.

I figured out I accidentally clicked a line number, which apparently sets breakpoints for debugging. I also might have somehow clicked "Toggle global breakpoint state" in the bottom Debug area.

Because I selected the line where the setImage was, it looked like the app crashed/froze whenever it hit that line, but it actually just paused the app to allow me to look at what's going on with the app and debug it. I deselected the lines and turned off the global breakpoint state button and everything runs fine now.

A newbie coder mistake from somebody not used to working in an IDE. :P

Setting the NSImage of a NSImageView from a NSURL

3 Answers3