Just as my title mentions, I want to use NSImageView, To "animate" an image, but not loop when it reaches the end of its animation.
The infinite loop of a gif image is not a bad habit of the NSImageView, it is determined by a value (in Application Extension) within the gif image data. You can ask for that value by
NSBitmapImageRep *gifRep = // get the gif image from wherever
NSInteger loopCount = [[gifRep valueForProperty: NSImageLoopCount] integerValue];
// a lopCount of zero means: infinite
But you can also set that value (before sending it to the NSImageView). If you want the animation to stop after one loop, do this:
NSImage *img = [[NSImage alloc] initWithContentsOfFile:fileName]; // or similar
NSBitmapImageRep *gifRep = [[img representations] objectAtIndex:0];
[gifRep setProperty:NSImageLoopCount withValue:@(1)]; //one loop, then stop
[myImageView setImage:img];