结合使用MVVM组合框的SelectedItem [英] Binding ComboBox SelectedItem using MVVM

问题描述

我有一个问题在的SelectedItem 在我的组合框。

I have a problem with the SelectedItem in my ComboBox.

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

如果我打开组合框，我看到的值。

If I open the ComboBox, I see the values.

如果我选择一个项目，所选项目将不会被显示。

有任何人的想法？

在我的ViewModel我有这两个属性：

In my ViewModel I have these two properties:

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

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

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

这是一些属性从类：

These are a few properties from the class :

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);
}

---

修改：
发生以下情况如果我删除了物业的DisplayMemberPath：

---

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

推荐答案

您似乎对你的组合框不必要地设置属性。您可以删除具有不同用途的DisplayMemberPath 和 SelectedValuePath 属性。这可能是一个想法，让你看看的<一个href=\"http://stackoverflow.com/questions/4902039/difference-between-selecteditem-selectedvalue-and-selectedvaluepath\">Difference的SelectedItem，的SelectedValue和SelectedValuePath之间张贴在这里对这些属性的解释。试试这个：

You seem to be unnecessarily setting properties on your ComboBox. You can remove the DisplayMemberPath and SelectedValuePath properties which have different uses. It might be an idea for you to take a look at the Difference between SelectedItem, SelectedValue and SelectedValuePath post here for an explanation of these properties. Try this:

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

此外，这是毫无意义的使用 displayPeriod 属性，如WPF框架将自动调用的ToString 方法它需要显示的对象不具有<​​code>的DataTemplate 为他们设置明确的。

Furthermore, it is pointless using your displayPeriod property, as the WPF Framework would call the ToString method automatically for objects that it needs to display that don't have a DataTemplate set up for them explicitly.

更新>>>

由于我不能看到所有的code，我不能告诉你，你在做什么错。相反，所有我能做的就是为您提供如何实现你想要的一个完整的工作的例子。我从你的类中删除无谓 displayPeriod 属性，并且还你的 SalesPeriodVO 财产我什么都不知道吧..也许这是你的问题的原因??。试试这个：

As I can't see all of your code, I cannot tell you what you are doing wrong. Instead, all I can do is to provide you with a complete working example of how to achieve what you want. I've removed the pointless displayPeriod property and also your SalesPeriodVO property from your class as I know nothing about it... maybe that is the cause of your problem??. Try this:

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，我添加了两个属性到我的code背后：

Then I added two properties into my code behind:

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"); }
}

然后初始化集合用的您的值：

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

然后绑定数据的只有的这两个属性到组合框：

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

这就是它......这一切你需要一个完美的工作的例子。您应该看到的项目的显示来自的ToString 方法的没有的你的 displayPeriod 属性。希望你可以从这个code例如制定出你的错误。

That's it... that's all you need for a perfectly working example. You should see that the display of the items comes from the ToString method without your displayPeriod property. Hopefully, you can work out your mistakes from this code example.

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