使用 MVVM 绑定 ComboBox SelectedItem

我有一个问题选定的项目 in my ComboBox.

<ComboBox Name="cbxSalesPeriods"
        ItemsSource="{Binding SalesPeriods}"
        DisplayMemberPath="displayPeriod"
        SelectedItem="{Binding SelectedSalesPeriod}"
        SelectedValuePath="displayPeriod"
        IsSynchronizedWithCurrentItem="True"/>

If I open the ComboBox, I see the values.

If I select an item, the selected Item won't be shown.

有人有想法吗？

在我的 ViewModel 中，我有这两个属性：

public ObservableCollection<SalesPeriodVM> SalesPeriods { get; private set; }

private SalesPeriodVM selectedSalesPeriod;
public SalesPeriodVM SelectedSalesPeriod
{
    get { return selectedSalesPeriod; }

    set 
    {
        if (selectedSalesPeriod != value)
        {
            selectedSalesPeriod = value;
            RaisePropertyChanged("SelectedSalesPeriod");
        }
    }
}

这些是该类的一些属性：

public SalesPeriodVO Vo
{
    get { return period; }
}

public int Year
{
    get { return period.Year; }
    set
    {
        if (period.Year != value)
        {
            period.Year = value;
            RaisePropertyChanged("Year");
        }
    }
}

public int Month
{
    get { return period.Month; }
    set
    {
        if (period.Month != value)
        {
            period.Month = value;
            RaisePropertyChanged("Month");
        }
    }
}

public string displayPeriod { 
    get
    {
        return this.ToString();
    }
}

public override string ToString()
{
    return String.Format("{0:D2}.{1}", Month, Year);
}

EDIT: The Following happens If I remove the Property DisplayMemberPath:

您似乎不必要地设置了您的属性ComboBox。您可以删除DisplayMemberPath and SelectedValuePath具有不同用途的属性。您可以看看SelectedItem、SelectedValue 和 SelectedValuePath 之间的区别 https://stackoverflow.com/questions/4902039/difference-between-selecteditem-selectedvalue-and-selectedvaluepath在此发布以获取这些属性的解释。尝试这个：

<ComboBox Name="cbxSalesPeriods"
    ItemsSource="{Binding SalesPeriods}"
    SelectedItem="{Binding SelectedSalesPeriod}"
    IsSynchronizedWithCurrentItem="True"/>

此外，使用您的displayPeriod属性，WPF 框架将其称为ToString方法自动用于需要显示但没有DataTemplate明确地为他们设置。

更新>>>

由于我看不到你的所有代码，我无法告诉你你做错了什么。相反，我所能做的就是为您提供一个完整的工作示例，说明如何实现您想要的目标。我已经删除了无意义的displayPeriod财产以及您的SalesPeriodVO来自您班级的财产，因为我对此一无所知...也许这就是您问题的原因？？尝试这个：

public class SalesPeriodV
{
    private int month, year;

    public int Year
    {
        get { return year; }
        set
        {
            if (year != value)
            {
                year = value;
                NotifyPropertyChanged("Year");
            }
        }
    }

    public int Month
    {
        get { return month; }
        set
        {
            if (month != value)
            {
                month = value;
                NotifyPropertyChanged("Month");
            }
        }
    }

    public override string ToString()
    {
        return String.Format("{0:D2}.{1}", Month, Year);
    }

    public virtual event PropertyChangedEventHandler PropertyChanged;
    protected virtual void NotifyPropertyChanged(params string[] propertyNames)
    {
        if (PropertyChanged != null)
        {
            foreach (string propertyName in propertyNames) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            PropertyChanged(this, new PropertyChangedEventArgs("HasError"));
        }
    }
}

然后我在视图模型中添加了两个属性：

private ObservableCollection<SalesPeriodV> salesPeriods = new ObservableCollection<SalesPeriodV>();
public ObservableCollection<SalesPeriodV> SalesPeriods
{
    get { return salesPeriods; }
    set { salesPeriods = value; NotifyPropertyChanged("SalesPeriods"); }
}
private SalesPeriodV selectedItem = new SalesPeriodV();
public SalesPeriodV SelectedItem
{
    get { return selectedItem; }
    set { selectedItem = value; NotifyPropertyChanged("SelectedItem"); }
}

然后初始化集合your values:

SalesPeriods.Add(new SalesPeriodV() { Month = 3, Year = 2013 } );
SalesPeriods.Add(new SalesPeriodV() { Month = 4, Year = 2013 } );

然后进行数据绑定only这两个属性为ComboBox:

<ComboBox ItemsSource="{Binding SalesPeriods}" SelectedItem="{Binding SelectedItem}" />

就是这样......这就是一个完美工作示例所需要的一切。您应该看到项目的显示来自ToString method without your displayPeriod财产。希望您能从这个代码示例中找出错误。