调用'UIImagePickerController didFinishPickingMediaWithInfo'iOS7 XCode时的大量CPU使用情况

Question

I noticed a huge CPU usage when I press 'Use Photo' on UIImagePickerController calling the proper method:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{

}

even if the method is empy! Here an image logging CPU usage while above method is called.

Top that I recorded was 169%. So wtf?!?

Answer 1

This is because size of the image that you are using is very large normally more than 2mb. So so a image resize before using it. here is the code snippet:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    if([[info objectForKey:UIImagePickerControllerMediaType] isEqualToString:@"public.image"]) {
    UIImage *originalImage = info[UIImagePickerControllerOriginalImage];

    if (!originalImage)
        return;

    // Optionally set a placeholder image here while resizing happens in background

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Set desired maximum height and calculate width
        CGFloat height = 640.0f;  // or whatever you need
        CGFloat width = (height / self.view.frame.size.height) * self.view.frame.size.width;

        // Resize the image
        UIImage * image = [originalImage resizedImage:CGSizeMake(width, height) interpolationQuality:kCGInterpolationDefault];

        //save/use the image here
        UIImageWriteToSavedPhotosAlbum(image, nil, nil, NULL);//for saving to camera roll
    });
}
}