objective-c – 声明并访问BOOL类方法

+(BOOL)isCameraDeviceAvailable
{
    BOOL isCameraAvailable=NO;
    if([UIImagePickerController issourceTypeAvailable:UIImagePickerControllersourceTypeCamera])
    {
        if([UIImagePickerController isCameraDeviceAvailable:UIImagePickerControllerCameraDeviceFront] || [UIImagePickerController isCameraDeviceAvailable:UIImagePickerControllerCameraDeviceRear])
            isCameraAvailable = YES;
    }
    return isCameraAvailable;
}

但是我不能正确地声明它并且得到了错误

Instance method '-isCameraDeviceAvailable' not found (return type defaults to 'id')

当我宣布如下.

+ (BOOL)isCameraDeviceAvailable;

然后以这种方式使用它

if([self isCameraDeviceAvailable]){
 }

我想我需要在不同的地方或以不同的方式宣布它.你能告诉我怎么做吗？