扫描完成后，Xamarin Zxing扫描仪写作逻辑

Question

我正在从事C＃Xamarin项目。在项目中，我使用了zxing.net.mobile类库来实现QR码扫描仪。

用户扫描QR码后，显示了一个URL。用于将数据发送到Web服务。我的问题是：在执行方法 connectTobackend 的中途中间。结果，执行 connectTobackend 永远不会完成。我需要有关如何处理此线程方案的帮助，以便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，当用户单击"扫描"按钮时，方法显示CannerPage使用ZXing.net移动库在其移动设备上打开扫描仪视图。我在下面有一个粘贴的班级。

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

您在没有await关键字的情况下调用异步函数（async void connectToBackend(String nodes)）。

我认为您可以定义" async"事件scanPage.OnScanResult += (result) => {，因此您可以async connectToBackend函数。

我认为BeginInvokeOnMainThread不是必需的