第一次和第二次单击后更改 gridViewItem 的背景颜色

问题描述

我的观点是在第一次点击后将 gridViewItem 的背景颜色更改为蓝色，在第二次点击后更改为红色，然后是蓝色，然后是红色 ...

My point is to change gridViewItem's background color to Blue after first click and to Red after second click on it, then Blue, then Red ...

这是我的 c# 代码，但它在gvi.Background = new SolidColorBrush(Windows.UI.Colors.Blue);"上抛出了一个异常System.NullReferenceException":

Here is my c# code but it threw an exception 'System.NullReferenceException' on "gvi.Background = new SolidColorBrush(Windows.UI.Colors.Blue);":

   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:

My Contact.cs in Models:

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！

Any help will be appreciated, thank you !

推荐答案

为什么不使用布尔值作为计数器?

Why not use a boolean as the counter?

   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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