条码扫描仪页面导航问题

Question

我有我遵循的条形码阅读器/扫描仪教程。在ScannerPage 中，当我单击一个按钮时，它将打开scanner，读取后，它将使用API​​ 将结果传递给数据库并返回给ScannerPage。 我有这个错误Page must not already have a parent 但我不知道为什么。如何解决这个问题？

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

您正在推送 scanPage 两次

    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

你是await Navigation.PushAsync(scanPage); 两次。

改成：

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);
}