Question

我正在开发一个C＃Xamarin项目。在项目中，我使用了ZXing.Net.Mobile类库来实现QR代码扫描程序。

用户扫描QR码后，会显示一个网址。用于将数据发送到Web服务。我的问题是：在执行方法 connectToBackend 期间，线程BeginInvokeOnMainThread到期。因此， connectToBackend 的执行永远不会完成。我需要有关如何处理此线程场景的帮助，以便我可以处理我的服务器请求。

public void ShowScannerPage() {

        ZXingScannerPage scanPage = new ZXingScannerPage();

        scanPage.OnScanResult += (result) => {

            // stop scanning
            scanPage.IsScanning = false;

            ZXing.BarcodeFormat barcodeFormat = result.BarcodeFormat;
            string type = barcodeFormat.ToString();


    // This thread finishes before the method, connectToBackend, inside has time to finish   
            Xamarin.Forms.Device.BeginInvokeOnMainThread(() => {

                 //_pageService.PopAsync();
                _pageService.PopAsync();


                App.UserDialogManager.ShowAlertDialog("The Barcode type is : " + type, "The text is : " + result.Text, " OK");

        // problem here 
                connectToBackend(result.Text);
            });

    // If I put connectToBackend here there is still a problem

        };

        _pageService.PushAsync(scanPage);

    }

为了提供更多信息，我正在使用MVVM方法。我有一个页面，当用户点击扫描按钮时，方法ShowScannerPage使用ZXing.Net Mobile库在其移动设备上打开扫描仪视图。我在下面粘贴了我的课程。

public class WorkoutViewModel {

    public ICommand ScanCommand { get; private set; }

    public readonly IPageService _pageService;

    public WorkoutViewModel(IPageService pageService) {

        this._pageService = pageService;

        ScanCommand = new Command(ShowScannerPage);

    }

    public void ShowScannerPage() {

        ZXingScannerPage scanPage = new ZXingScannerPage();

        scanPage.OnScanResult += (result) => {

            // stop scanning
            scanPage.IsScanning = false;

            ZXing.BarcodeFormat barcodeFormat = result.BarcodeFormat;
            string type = barcodeFormat.ToString();


    // This thread finishes before the method, connectToBackend, inside has time to finish   
            Xamarin.Forms.Device.BeginInvokeOnMainThread(() => {

                 //_pageService.PopAsync();
                _pageService.PopAsync();


                App.UserDialogManager.ShowAlertDialog("The Barcode type is : " + type, "The text is : " + result.Text, " OK");

        // problem here 
                connectToBackend(result.Text);
            });

    // If I put connectToBackend here there is still a problem

        };

        _pageService.PushAsync(scanPage);

    }

    public async void connectToBackend(String nodes) {

        // call api ...

    }

}

Answer 1

您正在调用不带async void connectToBackend(String nodes)关键字的异步函数（await）。

我认为您可以定义“async”事件scanPage.OnScanResult += (result) => {，以便您async connectToBackend功能。

我认为BeginInvokeOnMainThread不是必需的

Xamarin ZXing扫描仪在扫描完成后写入逻辑

1 个答案: