代码之家 › 专栏 › 技术社区 › Chris Dunaway

基于对另一个组合框的选择填充一个组合框

mvvm data-binding wpf

3

Chris Dunaway · 技术社区 · 15 年前

我正在学习wpf mvvm,并且一直在与我觉得可能很简单的事情作斗争,但我自己还没能解决。

我想要的是能够在填充的组合框中选择一个项目,然后基于该选择填充另一个组合框。我似乎无法加载第二个组合框来响应选择。

我已经包含了一个包含两个组合框和一个文本块的示例。当我运行应用程序并在第一个组合框中选择一个项目时,文本块会根据绑定进行更新,但我不知道在哪里调用代码来更新第二个组合框。

我尝试将调用添加到selectedString属性setter,但似乎从未调用过它。我肯定我错过了一些简单的东西,但我需要有人帮忙揭开面纱!

我尝试过其他帖子的建议,但到目前为止我还是没有成功。

以下是视图的XAML:

<Window x:Class="ThrowAwayMVVMApp.Views.MainView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Main Window" Height="400" Width="800">

    <DockPanel>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="60*" />
                <RowDefinition Height="282*" />
            </Grid.RowDefinitions>
            <!-- Add additional content here -->
            <ComboBox ItemsSource="{Binding MyStrings}" SelectedItem="{Binding Path=SelectedString, Mode=TwoWay}" Height="23" HorizontalAlignment="Left" Margin="18,24,0,0" Name="comboBox1" VerticalAlignment="Top" Width="204" />
            <TextBlock Text="{Binding SelectedString}" Height="23" HorizontalAlignment="Left" Margin="276,24,0,0" Name="textBlock1" VerticalAlignment="Top" Width="227" Background="#FFFAE7E7" />
            <ComboBox ItemsSource="{Binding ResultStrings}"  Height="23" HorizontalAlignment="Left" Margin="543,25,0,0" Name="comboBox2" VerticalAlignment="Top" Width="189" />
        </Grid>
    </DockPanel>
</Window>

这是视图模型:

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        this.MyStrings = new ObservableCollection<string>
            {
                "One",
                "Two",
                "Three",
                "Four",
                "Five"
            };
    }

    public ObservableCollection<string> MyStrings { get; set; }
    public ObservableCollection<string> ResultStrings { get; set; }

    public string SelectedString
    {
        get { return (string)GetValue(SelectedStringProperty); }
        set 
        { 
            SetValue(SelectedStringProperty, value);
            this.ResultStrings = getResultStrings(value);
        }
    }

    // Using a DependencyProperty as the backing store for SelectedString.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SelectedStringProperty =
        DependencyProperty.Register("SelectedString", typeof(string), typeof(MainViewModel), new UIPropertyMetadata(""));


    private ObservableCollection<string> getResultStrings(string input)
    {
        ObservableCollection<string> result = null;

        if (input == "Three")
        {
            result = new ObservableCollection<string> { "Six", "Seven", "Eight" };
        }
        else
        {
            result = new ObservableCollection<string> { "Nine", "Ten", "Eleven" };
        }

        return result;
    }
}

2 回复 | 直到 15 年前

1

2

Marco Amendola 15 年前

selectedString依赖项属性实现错误:应注册propertyChangedCallback,以便在直接访问DP时得到通知,而不是使用clr属性集(请参见 http://msdn.microsoft.com/en-us/library/system.windows.propertychangedcallback.aspx );这样,即使直接使用dp,也可以更改相关集合。

当绑定到依赖属性(如 SelectedString )wpf绑定不使用clr属性setter,因此永远不会 getResultStrings 打电话。

顺便说一句,我会考虑在视图模型上使用POCO方法,实现inotifypropertieschanged:dp是编写的一个难题,并且会给vms增加很多噪音(除了对system.windows的严重依赖)。

查看此博客文章进行广泛比较: http://kentb.blogspot.com/2009/03/view-models-pocos-versus.html

2

0

Agies 15 年前

尝试

private string selectedString;
public string SelectedString
{
    get { return selectedString; }
    set 
    { 
        if (selectedString == value) return;
        selectedString = value;
        // Required for the UI to know the change was successful
        RaisePropertyChanged("SelectedString");
        LoadStringResults(value);
    }
}

private ObservableCollection<string> resultStrings;
public ObservableCollection<string> ResultStrings
{
    get { return resultStrings; }
    set 
    { 
        if (resultStrings== value) return;
        resultStrings= value;
        // Required for databinding to know that ResultStrings changed
        // Previously you changed this property without updating the UI
        RaisePropertyChanged("ResultStrings");
    }
}

private void LoadStringResults(string input)
{
    ObservableCollection<string> result = null;

    if (input == "Three")
    {
        result = new ObservableCollection<string> { "Six", "Seven", "Eight" };
    }
    else
    {
        result = new ObservableCollection<string> { "Nine", "Ten", "Eleven" };
    }

    ResultStrings = result;
}