Question

从网络服务读取数据时，我尝试显示指示器，在网上搜索并与我的代码匹配后，具有以下代码以返回ListView和显示指示器，但指示器不显示。在主页中，单击“显示新闻”按钮并导航到新表单中的新表单初始形式后应包含以下代码：

private async void GetProduct()
{
    var indicator = new ActivityIndicator
    {
        HorizontalOptions = LayoutOptions.CenterAndExpand,
        Color = Color.Black,
        IsVisible = true
    };
    HttpClient httpClient = new HttpClient();
    var response = await httpClient.GetStringAsync("http://mySrvice.domain.com/api/news/getlastten");

    indicator.IsRunning = true;
    indicator.IsVisible = true;
    var TProducts = JsonConvert.DeserializeObject<List<News>>(response);
    Label header = new Label
    {
        Text = "Last ten news",
        FontSize = Device.GetNamedSize(NamedSize.Medium, typeof(Label)),
        HorizontalOptions = LayoutOptions.Center
    };

    ListView listView = new ListView
    {
        ItemsSource = TProducts,
        ItemTemplate = new DataTemplate(() =>
        {
            // Create views with bindings for displaying each property.
            Label nameLabel = new Label();
            nameLabel.SetBinding(Label.TextProperty, "Title");
            nameLabel.SetBinding(Label.FontFamilyProperty, "BNazanin.ttf#Nazanin");
            nameLabel.SetBinding(Label.HorizontalTextAlignmentProperty, "Start");



            Image nImage = new Image();
            nImage.SetBinding(Image.SourceProperty, "ImageURL");

            Label ViewdLabel = new Label();
            ViewdLabel.SetBinding(Label.TextProperty, "Viewed");

            nameLabel.SetBinding(Label.FontFamilyProperty, "BNazanin.ttf#Nazanin");

            // Return an assembled ViewCell.
            return new ViewCell
            {
                View = new StackLayout
                {
                    Padding = new Thickness(0, 5),
                    Orientation = StackOrientation.Horizontal,
                    FlowDirection = FlowDirection.RightToLeft,
                    Children =
                        {
                            nImage,
                            new StackLayout
                            {
                                VerticalOptions = LayoutOptions.Center,

                                Spacing = 0,
                                Children =
                                {

                                    nameLabel,
                                    ViewdLabel
                                }
                                }
                        }
                }
            };
        })
    };

    listView.ItemSelected += async (sender, e) =>
    {
        News = (News)e.SelectedItem;

        await Navigation.PushAsync(new NewsDetails(News));
    };
    this.Content = new StackLayout
    {
        Children =
        {
            indicator,
            header,
            listView
        }
    };
    indicator.IsRunning = false;
    indicator.IsVisible = false;
}

Answer 1

正如其他用户在评论中指出的那样，除非您将ActivityIndicator添加到页面中，否则不会出现。您正在将其添加到GetProduct()末尾的页面上，并立即使其不可见，因此它从不可见，这是因为尚未添加它，或者是因为它已被添加看不见的。

有几种可能性可以实现您想要的。最简单的方法是将ActivityIndicator的开头添加GetProducts()

var indicator = new ActivityIndicator
{
    HorizontalOptions = LayoutOptions.CenterAndExpand,
    Color = Color.Black,
    IsVisible = true,
    IsRunning = true
};
this.Content = indicator; 

HttpClient httpClient = new HttpClient();
var response = await httpClient.GetStringAsync("http://mySrvice.domain.com/api/news/getlastten");

（{IsRunning被立即设置，因为我假设您希望指示器在期间运行，而您是从服务器而不是之后从服务器获得产品的。）

您不需要在最终的堆栈布局中使用指示器，因此可以将Content设置为

this.Content = new StackLayout
{
    Children =
    {
        header,
        listView
    }
};

附带说明：使用XAML和MVVM对这些事情很有帮助。

Xamarin指示器未显示

1 个答案: