UIButton图像在“for”循环中不会发生变化

Question

i have a question:
I designed my GUI without the InterfaceBuilder,
now i want change the image of a button for a short period of time, but it won't change, until the whole for-loop has finished. What am i doing wrong?

    for (size_t i=0; i< 100; ++i){
      switch (variable) {
        case 0:
          [self changeRedButtonToWhite: redButton];
        break;
        case 1:
        ....
      }
    }

-(IBAction) changeRedButtonToWhite: (id)sender{
    [sender setBackgroundImage: whiteImage forState: UIControlStateNormal];
}

Answer 1

You can't use a for loop to do this, you should try using an NSTimer instead. The UI isn't refreshed while there is a loop going on inside the main thread.

Answer 2

@Luzal's explanation is correct. You're setting the background color of the button, but that only causes the button to be marked as needing to be redrawn. The redrawing doesn't happen (at least) until execution returns to the run loop, and that can't happen until your for loop finishes.

We can't tell from the code you posted what else you're doing in you for loop, but if you're using it as the delay mechanism and then changing the button color back to red when, say, variable hits 99, that's not a great plan anyway. You can use NSTimer to manage the duration of the color change, or -performSelector:afterDelay:, or use Core Animation.

Answer 3

将for循环放在后台线程上并在主线程上调用-changeRedButtonToWhite。

Answer 4

Can you not do the following?

Add all your buttons to an NSMutableArray , or just use NSArray if your not planning on adding more buttons to it after it has been allocated.

NSMutableArray *buttonsArray = [[NSMutableArray alloc] initWithObjects:button1, button2, button3, nil]; //and so on....

and then....

for(UIButton *button in buttonsArray){
     [button setBackgroundImage: whiteImage forState: UIControlStateNormal];
}