WPF - 自动刷新组合框的内容 [英] WPF - Auto refresh combobox content

问题描述

我得到的样本MVVM应用程序。用户界面有一个文本框，一个按钮和一个组合框。当我输入在文本框中的东西，按下按钮，我输入的文本被添加到一个ObservableCollection。组合框被绑定到该集合。我如何获得组合框全自动显示新添加字符串？

I got a sample mvvm app. The UI has a textbox, a button and a combobox. when I enter something in the textbox and hit the button, the text I enter gets added to an observablecollection. The Combobox is bound to that collection. How do I get the combobox to display the newly added string automaticly?

推荐答案

据我理解正确的话，您要添加的项并选择它。
下面是例子，如何可以使用视图模型和绑定完成

As I understand correctly, you want to add an item and select it. Here is the example how it can be done using ViewModel and bindings.

XAML中：

<StackPanel>
    <TextBox Text="{Binding ItemToAdd}"/>
    <ComboBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" />
    <Button Content="Add" Click="Button_Click"/>
</StackPanel>

视图模型：

ViewModel:

public class MainViewModel:INotifyPropertyChanged
{
    public ObservableCollection<string> Items { get; set; }

    public string ItemToAdd { get; set; }

    private string selectedItem;

    public string SelectedItem
    {
        get { return selectedItem; }
        set
        {
            selectedItem = value;
            OnPropertyChanged("SelectedItem");
        }
    }

    public void AddNewItem()
    {
        this.Items.Add(this.ItemToAdd);
        this.SelectedItem = this.ItemToAdd;
    }


    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

的

MainViewModel 有3个属性（一个用于文本框和另外两名为组合框）和方法 AddNewItem 不带参数。

The MainViewModel has 3 properties (one for the TextBox and two other for the ComboBox) and the method AddNewItem without parameters.

该方法可以从命令触发，但对于命令没有标准类，所以我将其称之为从后台代码：

The method can be triggered from a command, but there is no standard class for commands, so I will call it from the code-behind:

   ((MainViewModel)this.DataContext).AddNewItem();

因此​​，作为选择将其添加到集合后，必须明确设置添加的项目。

So you must explicitly set an added item as selected after you add it to a collection.

由于该方法 OnItemsChanged 组合框类>被保护， 'T被使用。

Because the method OnItemsChanged of the ComboBox class is protected and can't be used.

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