Turn on torch/flash on iPhone

Here's a shorter version you can now use to turn the light on or off:

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];if ([device hasTorch]) {    [device lockForConfiguration:nil];    [device setTorchMode:AVCaptureTorchModeOn];  // use AVCaptureTorchModeOff to turn off    [device unlockForConfiguration];}

UPDATE: (March 2015)

With iOS 6.0 and later, you can control the brightness or level of the torch using the following method:

- (void)setTorchToLevel:(float)torchLevel{    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];    if ([device hasTorch]) {        [device lockForConfiguration:nil];        if (torchLevel <= 0.0) {            [device setTorchMode:AVCaptureTorchModeOff];        }        else {            if (torchLevel >= 1.0)                torchLevel = AVCaptureMaxAvailableTorchLevel;            BOOL success = [device setTorchModeOnWithLevel:torchLevel   error:nil];        }        [device unlockForConfiguration];    }}

You may also want to monitor the return value (success) from setTorchModeOnWithLevel:. You may get a failure if you try to set the level too high and the torch is overheating. In that case setting the level to AVCaptureMaxAvailableTorchLevel will set the level to the highest level that is allowed given the temperature of the torch.

iWasRobbed's answer is great, except there is an AVCaptureSession running in the background all the time. On my iPhone 4s it takes about 12% CPU power according to Instrument so my app took about 1% battery in a minute. In other words if the device is prepared for AV capture it's not cheap.

Using the code below my app requires 0.187% a minute so the battery life is more than 5x longer.

This code works just fine on any device (tested on both 3GS (no flash) and 4s). Tested on 4.3 in simulator as well.

#import <AVFoundation/AVFoundation.h>- (void) turnTorchOn:(BOOL)on {    Class captureDeviceClass = NSClassFromString(@"AVCaptureDevice");    if (captureDeviceClass != nil) {        AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];        if ([device hasTorch] && [device hasFlash]){            [device lockForConfiguration:nil];            if (on) {                [device setTorchMode:AVCaptureTorchModeOn];                [device setFlashMode:AVCaptureFlashModeOn];                torchIsOn = YES;            } else {                [device setTorchMode:AVCaptureTorchModeOff];                [device setFlashMode:AVCaptureFlashModeOff];                torchIsOn = NO;                        }            [device unlockForConfiguration];        }    }}

See a better answer below: https://stackoverflow.com/a/10054088/308315

Old answer:

First, in your AppDelegate .h file:

#import <AVFoundation/AVFoundation.h>@interface AppDelegate : NSObject <UIApplicationDelegate> {    AVCaptureSession *torchSession;}@property (nonatomic, retain) AVCaptureSession * torchSession;@end

Then in your AppDelegate .m file:

@implementation AppDelegate@synthesize torchSession;- (void)dealloc {    [torchSession release];    [super dealloc];}- (id) init {    if ((self = [super init])) {    // initialize flashlight    // test if this class even exists to ensure flashlight is turned on ONLY for iOS 4 and above        Class captureDeviceClass = NSClassFromString(@"AVCaptureDevice");        if (captureDeviceClass != nil) {            AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];            if ([device hasTorch] && [device hasFlash]){                if (device.torchMode == AVCaptureTorchModeOff) {                NSLog(@"Setting up flashlight for later use...");                    AVCaptureDeviceInput *flashInput = [AVCaptureDeviceInput deviceInputWithDevice:device error: nil];                    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];                    AVCaptureSession *session = [[AVCaptureSession alloc] init];                [session beginConfiguration];                    [device lockForConfiguration:nil];                    [session addInput:flashInput];                    [session addOutput:output];                    [device unlockForConfiguration];                    [output release];                [session commitConfiguration];                [session startRunning];                [self setTorchSession:session];                [session release];                    }            }        }    }     return self;}

Then anytime you want to turn it on, just do something like this:

// test if this class even exists to ensure flashlight is turned on ONLY for iOS 4 and aboveClass captureDeviceClass = NSClassFromString(@"AVCaptureDevice");if (captureDeviceClass != nil) {    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];    [device lockForConfiguration:nil];    [device setTorchMode:AVCaptureTorchModeOn];    [device setFlashMode:AVCaptureFlashModeOn];    [device unlockForConfiguration];}

And similar for turning it off:

// test if this class even exists to ensure flashlight is turned on ONLY for iOS 4 and aboveClass captureDeviceClass = NSClassFromString(@"AVCaptureDevice");if (captureDeviceClass != nil) {    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];    [device lockForConfiguration:nil];    [device setTorchMode:AVCaptureTorchModeOff];    [device setFlashMode:AVCaptureFlashModeOff];    [device unlockForConfiguration];}