与在的ItemsSource IEnumerable的默认值替换NULL [英] Replace NULL with a default Value in an ItemsSource IEnumerable

问题描述

我有一个 自定义控制 衍生自 的ItemsControl

I'm having a Custom Control derived from an ItemsControl.

我接到的双向绑定的不明物体在发行WPF自定义控件依赖项属性

在上面的问题，他们使用集合中的视图模型

In the above Question, they use the Collection in the View Model

private ObservableCollection<string> _collection = new ObservableCollection<string>();

public ObservableCollection<string> Collection
{
    get { return _collection; }
    set
    {
        _collection = value;
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Collection"));
    }
}

该XAML代码是

The XAML Code is

<Window x:Class="SampleControl.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:SampleControl" 
        Title="MainWindow" Height="400" Width="525">
    <Grid>
        <local:BTextBox 
            ItemsSource="{Binding Collection}" 
            ProviderCommand="{Binding AutoBTextCommand}" 
            AutoItemsSource="{Binding SuggCollection}" />
    </Grid>
</Window>

如果我删除了新的ObservableCollection<串>（）; 那么它将成为

If I removed the new ObservableCollection<string>(); then it will became

private ObservableCollection<string> _collection;

public ObservableCollection<string> Collection
{
    get { return _collection; }
    set
    {
        _collection = value;
        if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Collection"));
    }
}

现在该物业的 收藏 保存值 NULL 。此属性是在的ItemsSource 绑定。所以，我怎么可能将数据推入的ItemsSource

Now the Property Collection hold the value NULL. This Property is bind in the ItemsSource. So, how could I push the data into the ItemsSource

CustomControl方法是

The CustomControl Method is

private static void OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) {
    var tb = d as BTextBox;
    if ((e.NewValue != null) && ((tb.ItemsSource as IList) != null)) {
        foreach (var item in e.NewValue as IEnumerable) {
            (tb.ItemsSource as IList).Add(item);
        }
    }
}

在该方法中，将检查对于 NULL ，如果的ItemsSource 为 NOT NULL ，然后它推动数据。

In this method, it checks for NULL, IF the ItemsSource is NOT NULL, then it pushes the data.

IF（（e.NewValue！= NULL） &功放;及（！（tb.ItemsSource为IList的）= NULL））。如果在 的ItemsSource 为 NOT NULL ，然后才把项目被推到集合（tb.ItemsSource作为IList的）。新增（项目）;

请帮助我，如何分配值在 为空的的IEnumerable ？

Kindly assist me, how to assign the Value in a Null-able IEnumerable ?

推荐答案

我们可以添加项目，添加项目之前，我们需要创建一个实例

We Can add the Item, before adding the Item we need to create an Instance

if(this.ItemsSource == null)
{
    this.ItemsSource = (new List<object>()).AsEnumerable();
}

(tb.ItemsSource as IList).Add(item);

现在，它不会引发任何的 NULL 参考例外

Now, it won't throw any NULL Reference exception.

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