need to dim iphone screen while my app is running

Question

I don't want the phone to go to sleep so I am using:

    [ [ UIApplication sharedApplication ] setIdleTimerDisabled:YES ] ;

but I do need the phone to gray out its screen to not waste the battery. I have already seen this question How can I dim the view in an iPhone application?, but need more detail please.

I am trying something like this:

to set the opaqueWindow as frontmost (which has a 320 x 480 black image loaded)

[opaqueWindow makeKeyAndVisible];
[ opaqueWindow setAlpha:1.00 ] ;        
[ mainWindow setAlpha:0.10 ] ;

and to try to go back to the mainWindow and set it frontmost (a picker control and some labels):

    [ opaqueWindow setAlpha:0 ] ;       
    [mainWindow makeKeyAndVisible];
    [ mainWindow setAlpha:1.00 ] ;

There can only be one key window in my app, right? so when mainWindow becomes key, then opaqueWindow isn't and vice versa. I create opaqueWindow and access mainWindow as follows:

    opaqueWindow = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen ] bounds]];
    opaqueView = [[UIView alloc] init];
    [opaqueWindow addSubview:opaqueView];

mainWindow = [ myApplication keyWindow ] ;

Even when I try to make my mainWindow active again, my controls are still grayed out and opaqueWindow still seems to have control.

I am a newbie at iphone development, I have been looking at the Cocoa Touch for iphone 3 developer reference and a few other books.

I would appreciate any help or advice.

thank you!

Piesia

Edit: I'm assuming that opaqueWindow will need to pass down button clicks to mainWindow while opaqueWindow is key. Do I just call mainWindow's button handler from within opaqueWindow's button handler or is there a better way to do it. thanks! P.

Answer 1

As of iOS 5 you can use the public API:

[[UIScreen mainScreen] setBrightness:1.0];//replace 1.0 with any value...

Beats using the opacity frame thing...

Answer 2

While it might make sense from a usability perspective, I doubt that overlaying the window with a gray view actually improves battery run time. You would have to dim the backlight, which is the main energy drain. This is only possible with a jailbroken phone or maybe a private API (which will prevent your app from being approved by Apple).

Use this method in your view controller to dim by adding a black view with 50% alpha. Make sure to set userInteractionEnabled = NO to pass events to underlying views.

- (IBAction)dim:(id)sender {
    UIView *dimView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];
    dimView.backgroundColor = [UIColor blackColor];
    dimView.alpha = 0.5f;
    dimView.userInteractionEnabled = NO;
    [self.view addSubview:dimView];
}

In case you want to push your luck and risk being rejected, try this private API call:

[(id)[UIApplication sharedApplication] setBacklightLevel:1.0f];