在第一次和第二次单击后更改 gridView Items 背景颜色

Question

我的意思是在第一次单击后将 gridViewItem 的背景颜色更改为蓝色，在第二次单击后更改为红色，然后是蓝色，然后是红色...

这是我的 c# 代码，但它在“gvi.Background = new SolidColorBrush(Windows.UI.Colors.Blue);”上引发了异常“System.NullReferenceException”：

   private void GridViewItem_Click (Object sender, ItemClickEventArgs e)
    {
        if(e!=null)
        {

            for (int numberOfClick= 1; numberOfClick <100; ++numberOfClick)
            {
                GridViewItem gvi = (GridViewItem)NameOf_ItemClick.ContainerFromItem(e);

                if (numberOfClick % 2 == 0)
                {

                    gvi.Background = new SolidColorBrush(Windows.UI.Colors.Red);

                }
                else
                {
                    gvi.Background = new SolidColorBrush(Windows.UI.Colors.Blue);
                }
            }

        }
    }

这是我的Xaml 代码：

<Page
x:Class="HNT_listView2.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:HNT_listView2"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:data="using:HNT_listView2.Models"
mc:Ignorable="d">

<Grid Background= "Salmon" Margin="0,0,10,0"  >

    <GridView ItemsSource="{x:Bind MyContactList}" 
              ItemClick="GridViewItem_Click" Name="NameOf_ItemClick"
              IsItemClickEnabled="True" >


        <GridView.ItemTemplate>
            <DataTemplate x:DataType="data:Contact">
                <StackPanel >
                    <FlyoutBase.AttachedFlyout>
                        <MenuFlyout Placement="Top">
                            <MenuFlyoutItem Text="Call"/>
                            <MenuFlyoutItem Text="Send a message"/>
                            <MenuFlyoutItem Text="Delete"/>
                        </MenuFlyout>
                    </FlyoutBase.AttachedFlyout>

                    <StackPanel HorizontalAlignment="Center" Orientation="Horizontal">


                    <Image Width="100" Height="120" Source="{x:Bind Photo}" HorizontalAlignment="Center" Stretch="UniformToFill"/>
                    <StackPanel Orientation="Vertical">
                        <TextBlock FontSize="30" Text="{x:Bind Name}" HorizontalAlignment="Center"/>
                        <TextBlock FontSize="30" Text="{x:Bind Phone}" HorizontalAlignment="Center"/>
                    </StackPanel>
                </StackPanel>
                </StackPanel>
            </DataTemplate>
        </GridView.ItemTemplate>

    </GridView>


</Grid>

模型中的我的 Contact.cs：

public class Contact
{
    public string Name { get; set; }
    public string Photo { get; set; }
    public string Phone { get; set; }
}


public class ContactManager
{
    public static List<Contact> GetContacts()
    {
        var contact1 = new List<Contact>();
        contact1.Add(new Contact { Name = "Nguyen Van A", Phone = "0168111222", Photo = "Assets/1.jpg" });
        contact1.Add(new Contact { Name = "Tran Van B", Phone = " 0168333444", Photo = "Assets/2.jpg" });
        contact1.Add(new Contact { Name = "Le Van C", Phone = "0166555666", Photo = "Assets/3.jpg" });

        return contact1;
    }
}

任何帮助将不胜感激，谢谢！

Answer 1

为什么不使用布尔值作为计数器？

   private byte GridViewSwitch = 0;
   private void GridViewItem_Click (Object sender, ItemClickEventArgs e)
    {
        if(e!=null)
        {
            var item = (GridViewItem)NameOf_ItemClick.ContainerFromItem(e);
            switch(GridViewSwitch)
            case 0 : item.Background = new SolidColorBrush(Windows.UI.Colors.Red); GridViewSwitch++;  break ;
           case 1 : item.Background = new SolidColorBrush(Windows.UI.Colors.Blue); GridViewSwitch++;   break ;

            case 2: item.Background = new SolidColorBrush(Windows.UI.Colors.Green); GridViewSwitch=0;   break ;

        }
    }

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