Question

我有遵循的本条形码阅读器/扫描器教程。在ScannerPage中，当我单击一个按钮时，它将打开scanner，并且在读取后，它将使用API将结果传递到数据库，并返回到ScannerPage。我遇到此错误Page must not already have a parent，但我不知道为什么。怎么解决呢？

private async  void Button_Clicked(object sender, EventArgs e)
    {
        scanPage = new ZXingScannerPage();
        await Navigation.PushAsync(scanPage);
        scanPage.OnScanResult += (result) => 
        {
            Device.BeginInvokeOnMainThread( async() => 
            {
                await Navigation.PopAsync();
                //send something using WEB API
            });
        };
        await Navigation.PushAsync(scanPage);
    }

Answer 1

您两次按下scanPage

    scanPage = new ZXingScannerPage();

    // this is not needed
    // await Navigation.PushAsync(scanPage);

    scanPage.OnScanResult += (result) => 
    {
        Device.BeginInvokeOnMainThread( async() => 
        {
            await Navigation.PopAsync();
            //send something using WEB API
        });
    };

    // navigate here, AFTER you have defined your OnScanResult handler
    await Navigation.PushAsync(scanPage);

Answer 2

您两次成为await Navigation.PushAsync(scanPage);。

将其更改为：

private async  void Button_Clicked(object sender, EventArgs e)
{
    scanPage = new ZXingScannerPage();
    scanPage.OnScanResult += (result) => 
    {
        Device.BeginInvokeOnMainThread( async() => 
        {
            await Navigation.PopAsync();
            //send something using WEB API
        });
    };
    await Navigation.PushAsync(scanPage);
}

条形码扫描仪页面导航问题

2 个答案: