ActivityIndicator 未以 xamarin 形式显示

Question

///ActivityIndicator defined in xmal 

 <ActivityIndicator x:Name="popupView"  VerticalOptions="Center" HorizontalOptions="Center"  Color="DarkBlue"  IsRunning="True" IsVisible="false" IsEnabled="True" />

在我的 C# 代码中：

 popupView.IsVisible = true;

for (int i = 0; i < item.Count; i++)
                {
                    dataGrid.Children.Add(new Label
                    {
                        Text = item[i].Value,
                        TextTransform = TextTransform.None,
                        HorizontalTextAlignment = TextAlignment.Center,
                        TextColor = Color.Black,
                        Padding = 1,
                        WidthRequest = 200,
                        BackgroundColor = Color.LightGray

                    }, i, j + 1);
                }

 popupView.IsVisible = false;

ActivityIndicator is not shown. What should I do?

Answer 1

尝试使用主线程中的代码。

Device.BeginInvokeOnMainThread(() =>
    { popupView.IsVisible = true;

            for (int i = 0; i < item.Count; i++)
                {
                    dataGrid.Children.Add(new Label
                    {
                        Text = item[i].Value,
                        TextTransform = TextTransform.None,
                        HorizontalTextAlignment = TextAlignment.Center,
                        TextColor = Color.Black,
                        Padding = 1,
                        WidthRequest = 200,
                        BackgroundColor = Color.LightGray

                    }, i, j + 1);
                }

 popupView.IsVisible = false;
     });

Answer 2

为了看到 activity 指标，需要在某处进行延迟。

大概这是您正在做的测试，您的“真实”代码将“需要足够的时间”才能看到 activity 指标。

这是一种有效的方法。使用“睡眠”模拟您的代码需要时间。

xaml:

<!-- give appropriate name to your indicator. "popupView" sounds like a different type of element. -->
<!-- Use "IsRunning" to control visibility of ActivityIndicator, not "IsVisible". -->
<ActivityIndicator x:Name="indicator" VerticalOptions="Center" HorizontalOptions="Center" Color="DarkBlue" />

cs:

// Use "IsRunning" to control visibility of ActivityIndicator.
indicator.IsRunning = true;

Task.Run( () =>
{
    // This code runs on background thread.
    for (int i = 0; i < item.Count; i++)
    {
        // Simulate an operation that takes time.
        System.Threading.Thread.Sleep(500);
        ...
    }

    Device.BeginInvokeOnMainThread( () =>
    {
        // This code runs on MainThread.
        indicator.IsRunning = false;
    });
});

注意说明哪些代码在后台线程上运行，哪些代码在 MainThread 上运行的注释。

Answer 3

根据你的代码，我做了一个简单的demo，运行正常。

您可以参考以下代码：

MainPage.xaml

<StackLayout>
    <ActivityIndicator x:Name="popupView"  VerticalOptions="Start" HorizontalOptions="FillAndExpand"   IsRunning="True" IsEnabled="True"  IsVisible="false"   Color="Red"      />

    <Grid x:Name="dataGrid" ></Grid>

    <Button Text="test" Clicked="Button_Clicked"  HorizontalOptions="FillAndExpand" HeightRequest="50"/>
</StackLayout>

MainPage.xaml.cs

    private void Button_Clicked(object sender, EventArgs e)
    {
        popupView.IsVisible = true;


        Task.Run(() => {

            Device.BeginInvokeOnMainThread(() => {

                int j = 0;

                for (int i = 0; i < 30; i++)
                {

                    dataGrid.Children.Add(new Label
                    {
                        Text = "test:" + i,
                        TextTransform = TextTransform.None,
                        HorizontalTextAlignment = TextAlignment.Center,
                        TextColor = Color.Black,
                        Padding = 1,
                        WidthRequest = 200,
                        BackgroundColor = Color.LightGray

                    }, i, j + 1);

                    j = 0;
                }

                popupView.IsVisible = false;
            });
        });
    }

ActivityIndicator 未以 xamarin 形式显示

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ActivityIndicator 未以 xamarin 形式显示