尝试执行方法调用时使用未声明的标识符错误

Question

I am using the AV Foundation framework. I am trying to perform a method call of "deviceInputWithDevice" for an "AVCaptureDeviceInput" object.

The problem is that the method call contains an "error" parameter that I have named "error" and I keep getting this warning in xcode: Use of undelcared identifier 'error'

All of my AV Foundation code is located in the View Controller's ViewDidLoad method implementation. Here it is:

    AVCaptureSession *session = [[AVCaptureSession alloc]init];

    session.sessionPreset = AVCaptureSessionPresetHigh;

    AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:error];

    [session addInput:input];

I can't figure out why it keeps giving me the undeclared identifier warning for the "error" parameter.

Any help is greatly appreciated.

Answer 1

You have to declare the error variable that you are trying to use:

NSError *error = nil;
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

And note that you need an & before error when you pass it to the method. And of course you should check it:

if (input) {
    // it succeeded, do something
} else {
    NSLog(@"Error trying to call deviceInputWithDevice: %@", error);
}