screen brightness control

Am developing a ebook reader(just like ibook) for that i need to control the screen brightness of the background on image click in iphone. i did this.

background.m

-(void)brightness
{
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    UIImage *image = [UIImage imageNamed:@"brightness.jpg"];
    button.frame = CGRectMake(0, 0, image.size.width, image.size.height);
    [button setImage:image forState:UIControlStateNormal];

    UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];
    UIImage *image1 = [UIImage imageNamed:@"brightness.jpg"];
    button1.frame = CGRectMake(0, 0, image1.size.width, image1.size.height);
    [button1 setIma开发者_JS百科ge:image forState:UIControlStateNormal];
    [button1 addTarget:self action:@selector(brightnessControl:) forControlEvents:UIControlEventTouchUpInside];

    gBrightnessSetting=100;

    brightnessOverlay = [[CALayer alloc] init];
    brightnessOverlay.masksToBounds = YES;
    brightnessOverlay.backgroundColor = [[[UIColor blackColor] colorWithAlphaComponent:1.0] CGColor];
    brightnessOverlay.opacity = 0.0;
    [self.layer addSublayer:brightnessOverlay];

    bottomButtonsSize = SCREENWIDTH/5;

}

- (void)dealloc {
    [brightnessLessButton release];
    [brightnessMoreButton release];

    [super dealloc];
}
- (void) setLayerFrames {
    brightnessOverlay.frame = CGRectMake(self.layer.bounds.origin.x,self.layer.bounds.origin.y,self.bounds.size.width,self.layer.bounds.size.height);
}

-(void)brightnessControl:(id)sender
 {  
    if(brightnessOverlay.opacity <= 0.05) {
    }else{
        double newBrightness = (brightnessOverlay.opacity-0.15);
        brightnessOverlay.opacity = newBrightness;
        NSLog(@"BRIGHTNESS FLOAT %f",brightnessOverlay.opacity);
        gBrightnessSetting=100-(int)(newBrightness*100);
        NSLog(@"BRIGHTNESS Value %d%%",gBrightnessSetting);
    }

}

and am calling dis in ebook.m like this,

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

   if ([indexPath row]==0) {
       background *back=[[background alloc] init];
       [back brightness];

       [self.view addSubview:back];

    }
}

What's wrong with my code...when am pressing that brightness option my app getting crashed.any suggestions.

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iOS 5.0 , you can use [[UIScreen mainScreen]setBrightness:1.0];

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As it is obvious, there is no public API for doing this.

One way (may not be a better way) of doing this is to change the colors of your views, texts in your app between dimmer and brighter colors.

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There is no Apple documented way of achieving the brightness control of screen !

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Use the debugger and find out which line of code is causing the crash.

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There is a private API call, but if you use it you will surely be rejected

GSEventSetBacklightLevel(0.5f);