并非每次都调用AVCapturePhotoCaptureDelegate方法

我正在制作一台定制相机,但结果不稳定。当我试图捕捉图像时,我 有时 未收到预期的委托回调。例如,以下是我的委托方法:

func photoOutput(_ output: AVCapturePhotoOutput, willBeginCaptureFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
    print("will begin")
}

func photoOutput(_ output: AVCapturePhotoOutput, willCapturePhotoFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
    print("will capture")
}

func photoOutput(_ output: AVCapturePhotoOutput, didCapturePhotoFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
    print("did capture")
}

func photoOutput(_ output: AVCapturePhotoOutput, didFinishCaptureFor resolvedSettings: AVCaptureResolvedPhotoSettings, error: Error?) {
    print("finished capture")
}

func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
    print("finish process")
}

我有一个按钮,可以触发以下方法:

func capture() {
    print("capture called")
    let settings = AVCapturePhotoSettings()
    captureOutput.capturePhoto(with: settings, delegate: self)
}

每次调用此方法时,我都会在控制台中看到以下输出:

capture called

will begin
will capture
did capture
finish process
finished capture
image set

然而,我只得到以下输出的可能性似乎是50/50:

capture called
did capture

这是怎么回事?