为什么这个 UWP ComboBox 初始化后可以为空，但可以正常选择? [英] Why this UWP ComboBox can be blank after initialization but works fine for selection?

问题描述

我有一个这样的组合框

<ComboBox
    Grid.Column="1"
    Padding="5,0,0,0"
    DisplayMemberPath="Description" 
    SelectedItem="{Binding MaxXXAge, Mode=TwoWay, Converter={StaticResource MaxXXAgeToMaxXXAgeMemberConverter}}"
    ItemsSource="{Binding ElementName=SettingsXXScrollViewer, Path=DataContext.MaxXXAgeMemberGroup, Mode=OneWay}" />

但是，初始化后，combobox是空白的.在此之后它实际上工作正常.我可以按预期选择并显示所选项目.这只是第一眼不起作用.但是，我已经初始化了 MaxXXAge 并且转换器已被触发.这是群

However, after initialization, the combobox is blank. It actually works fine after this. I can select and show the selected item as expected. It's just the first glance doesn't work. However, I already initialized MaxXXAge and the converter has been triggered. Here is the group

public IReadOnlyList<MaxXXAgeMembers> MaxXXAgeMemberGroup { get { return MaxXXAgeMembers.Options; } }

这是 MaxXXAgeMembers 的定义

And this is the definition for MaxXXAgeMembers

public class MaxXXAgeMembers
        {
            public MaxXXAge MaxXXAge { get; private set; }
            public string Description { get; private set; }

            public static readonly IReadOnlyList<MaxXXAgeMembers> Options = new ReadOnlyCollection<MaxXXAgeMembers>(new[]
            {
                new MaxXXAgeMembers { MaxXXAge =  MaxXXAge.OneDay, Description = Strings.SettingSync_OneDay},
.......
            });

            public static MaxXXAgeMembers FromMaxXXAge(MaxXXAge maxXXAge)
            {
                return Options.First(option => option.MaxXXAge == maxXXAge);
            }
        }

//稍后添加覆盖相等

public override bool Equals(object obj)
{
     if (obj == null || !(obj is MaxEmailAgeMembers))
          return false;
     return ((MaxEmailAgeMembers)obj).Description.Equals(this.Description);
}

public override int GetHashCode()
{
     return this.Description.GetHashCode();
}

转换器是这样的

public sealed class MaxEmailAgeToMaxEmailAgeMemberConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        return WPSettingsEmailViewModel.MaxEmailAgeMembers.FromMaxEmailAge((MaxEmailAge)value);
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        return ((WPSettingsEmailViewModel.MaxEmailAgeMembers)value).MaxEmailAge;
    }
}

有什么想法吗?

推荐答案

我对ItemResource使用了x:Bind，并在后面的代码中添加了ViewModel，解决了这个问题.

I used x:Bind for the ItemResource and added ViewModel inside code behind, and solved this problem.

这篇关于为什么这个 UWP ComboBox 初始化后可以为空，但可以正常选择?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！