Changing Backlight Level, iPhone

Question

I searched around for a way to set the backlight level within an app on the iPhone. I found a solution here:

http://www.iphonedevsdk.com/forum/29097-post3.html

The problem I have is, when I add this to my app I get an error and a warning. My code is as follows:

#include "GraphicsServices.h"

- (void) viewWillAppear:(BOOL)animated
{

NSNumber *bl = (NSNumber*) CFPreferencesCopyAppValue(CFSTR("SBBacklightLevel" ), CFSTR("com.apple.springboard"));
previousBacklightLevel = [bl floatValue];
//Error here : incompatible types in assignment

[bl release];   

GSEventSetBacklightLevel(0.5f);
// Warning here : implicit declaration of function 'GSEventSetBacklightLevel'

}

//...The rest of my app

- (void)applicationWillTerminate:(UIApplication *)TheNameOfMyAppIsHere
{
    GSEventSetBacklightLevel(previousBacklightLevel);
}

I am unsure of what is causing this. I also don't really know what needs to be in my .h file here, but I have:

NSNumber *previousBacklightLevel;

EDIT// Changed

NSNumber *previousBacklightLevel 

to

float previousBacklightLevel;

as suggested and this sorted the incompatible types in assignment error.

Now left with:

"_GSEventSetBacklightLevel", referenced from:

-[MyAppViewController viewWillAppear:] in MyAppViewController.o

-[MyAppViewController applicationWillTerminate] in MyAppViewController.o

symbol(s) not found

collect2: ld returned 1 exit status

Not sure how to fix this one either!

Any help would be appreciated,

// EDIT

All problems sorted. Thanks to all who helped me out. I really do appreciate it and can't wait till I can give a little back, by answering some questions.

Many thanks,

Stu

Answer 1

you can add the private framework by jus drag and drop to your xcode project from /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.2.sdk/System/Library/PrivateFrameworks/GraphicsServices.framework and also import the #import "GraphicsServices.h" header in your .h file

Answer 2

The reason you are getting a warning is because GSEventSetBacklightLevel() is a private API not declared in any of of the SDK headers. If you are planning to submit this to the app store your app will get rejected if you call it. If this is for a jailbroken device, you can just declare the function yourself.

void GSEventSetBacklightLevel(float level);

The reason you are getting the error is because you are trying to assign a float (which is a scalar) to an NSNumber *. You probably want to change previousBacklightLevel to be a float.