Xamarin 中 QR 扫描后的处理对话框

我在Xamarin应用程序中使用QR码扫描仪，当它扫描QR码时，它会执行一些操作，大约需要一分钟，而在执行操作时，我想在屏幕上显示一个加载对话框。但是，它没有显示在屏幕上，并且在应用程序的其他地方，它运行得很好。

Code

var expectedFormat = ZXing.BarcodeFormat.QR_CODE;
var opts = new ZXing.Mobile.MobileBarcodeScanningOptions { PossibleFormats = new List<ZXing.BarcodeFormat> { expectedFormat } };
var scanner = new ZXing.Mobile.MobileBarcodeScanner();
var result = await scanner.Scan(opts);
if (result == null)
{
    // code

    return null;
}
else
{
    using (UserDialogs.Instance.Loading("Processing"))
    {
        // code
    }
}

更新代码示例

public async Task Verification(object sender, EventArgs e)
{
    try
    {
        var expectedFormat = ZXing.BarcodeFormat.QR_CODE;
        var opts = new ZXing.Mobile.MobileBarcodeScanningOptions { PossibleFormats = new List<ZXing.BarcodeFormat> { expectedFormat } };
        var scanner = new ZXing.Mobile.MobileBarcodeScanner();
        var result = await scanner.Scan(opts);
        if (result == null)
        {
            // Code
            
            return null;
        }
        else
        {
            try
            {
                // QR Scan Result
                string qr_scan = result.Response;

                var result = JsonConvert.DeserializeObject<QRScan>(qr_scan);

                await CreateConnection();
            }
            catch (Exception error)
            { }
            finally
            {
                // navigate to next page
                await NavigationService.NavigateToAsync<NextViewModel>();
            }
        }
    }
    catch (Exception error)
    { }

    return null;
}

public async Task CreateConnection()
{
    UserDialogs.Instance.Loading("Processing");
     
    if ()
    {
        try
        {
            // Code
        }
        catch (Exception error)
        {
            // Code
        }
        finally
        {
            await CreateFolder(default, default);
        }
    }
}

public async Task CreateFolder(object sender, EventArgs e)
{
    UserDialogs.Instance.Loading("Processing");

    try
    {
        // Code
    }
    catch (Exception error)
    {
        // Code
    }

    return null;
}  

您可以使用Xamarin.Essentials https://learn.microsoft.com/en-us/xamarin/essentials/' 主线程 https://learn.microsoft.com/en-us/xamarin/essentials/main-thread?content=xamarin/xamarin-forms类，更具体地说 -InvokeOnMainThreadAsync方法。此方法的想法是不仅在 UI/主线程上执行代码，而且还要等待它的代码。这样您就可以同时拥有异步/等待逻辑和主线程执行。

try
{
    // QR Scan Result
    string qr_scan = result.Response;
    var result = JsonConvert.DeserializeObject<QRScan>(qr_scan);
    await MainThread.InvokeOnMainThreadAsync(() => CreateConnection());
}
catch (Exception error)
{ }
finally
{
    // navigate to next page
    await NavigationService.NavigateToAsync<NextViewModel>();
}

请记住，如果该方法CreateConnection执行时间较长，那么最好只在主线程上执行对话框呈现（UserDialogs.Instance.Loading("")).