jpg images in iphone and 2x images

Question

I am working on an iphone app and targeting iOS 4.0 or later. I am trying to add an image to UIImageView, and image is in jpeg format. This i

Answer 1

You just need to provide the full name of image.

bgImageView.image = [UIImage imageNamed:@"background.jpg"]; 

don't leave off the extension.

As for the @2x, it is not necessary to call it out anywhere in the code. If you code correctly there is no need to test for a retina display as some here have suggested.

Answer 2

According to the UIImage Class Reference:

Discussion

This method looks in the system caches for an image object with the specified name and returns that object if it exists. If a matching image object is not already in the cache, this method loads the image data from the specified file, caches it, and then returns the resulting object.

On a device running iOS 4 or later, the behavior is identical if the device’s screen has a scale of 1.0. If the screen has a scale of 2.0, this method first searches for an image file with the same filename with an @2x suffix appended to it. For example, if the file’s name is button, it first searches for button@2x. If it finds a 2x, it loads that image and sets the scale property of the returned UIImage object to 2.0. Otherwise, it loads the unmodified filename and sets the scale property to 1.0. See iOS Application Programming Guide for more information on supporting images with different scale factors. Special

Considerations

On iOS 4 and later, the name of the file is not required to specify the filename extension. Prior to iOS 4, you must specify the filename extension.

Since you're targeting iOS 4.0 and later, you should not need the filename extension. I tried to reproduce this potential bug, but it worked as expected for me without the filename extensions.

Here are some ideas for what may have gone wrong to create this effect in your app:

1. It's possible that the problem comes from the cache if you changed your images at some point.

2. If you choose not to use the filename extensions, and you have both "background.jpg" and "background.png" as options, the preference appears to be to use the ".png" file.

3. If you set the target to iOS 4.0 and later after first running the app, then the filename extension would have been required and the image may have been cached blank, which leads back to theory 1.

That's the best I can make of this.

Answer 3

You can use jpgs, just tried it myself and it worked. Only suggestion is how you are instantiating it. Try it this way:

stockImage = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"Morbo.jpg"]];

stockImage.frame = CGRectMake(0,0, self.view.bounds.size.width, self.view.bounds.size.height)  ;

[self.view addSubview:stockImage];

This is the image I used:

http://futurama.wikia.com/wiki/File:Morbo.jpg

Answer 4

Write a wrapper to get the image like

-(UIImage*) getImage:(NSString*)imageName{

    UIImage *image;

    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)] == YES && [[UIScreen mainScreen] scale] == 2.00) {

        // RETINA DISPLAY
        NSString *jpegFile = [imageName stringByAppendingString:@"@2x.jpg"];
        image = [UIImage imageNamed:jpegFile];
    }
    else{

        NSString *jpegFile = [imageName stringByAppendingString:@".jpg"];
        image = [UIImage imageNamed:jpegFile];
    }

    return image;
}

And from your code call

bgImageView.image                   =   getImage(@"background");

Answer 5

With the dawn of Xcode 6 I have found that JPG images might not render at all on certain iOS7 devices (they may work on some but not on others, or they may not work on any, and you may see a different result on a different developers machine, there doesn't seem to be any consistency). This is regardless of whether the image is just referenced in UIImageView in a XIB or programmatically with [UIImage imageNamed:] (which returns nil).

After scratching my head for a long time, the solution was to rename the *.jpg file extension to *.png (whilst obviously leaving the file contents as JPG data).

HTH