使用 MVVM 绑定 ComboBox SelectedItem

Question

我的 ComboBox 中的 SelectedItem 有问题。

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

如果我打开 ComboBox，我会看到值。

如果我选择一个项目，所选项目将不会显示。

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);
}

---

编辑： 如果我删除属性 DisplayMemberPath，会发生以下情况：

Answer 1

您似乎在您的ComboBox 上设置了不必要的属性。您可以删除具有不同用途的DisplayMemberPath 和SelectedValuePath 属性。您可以在此处查看Difference between SelectedItem, SelectedValue and SelectedValuePath 帖子以了解这些属性的说明。试试这个：

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

此外，使用 displayPeriod 属性毫无意义，因为 WPF 框架会自动为需要显示的对象调用 ToString 方法，而这些对象没有明确设置 DataTemplate。

---

更新>>>

由于我看不到您的所有代码，因此我无法告诉您您做错了什么。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。我已经从您的班级中删除了毫无意义的displayPeriod 属性以及您的SalesPeriodVO 属性，因为我对此一无所知……也许这就是您的问题的原因？？试试这个：

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"); }
}

然后用你的值初始化集合：

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

然后数据只将这两个属性绑定到ComboBox：

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

就是这样......这就是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 方法没有您的displayPeriod 属性。希望您可以通过此代码示例解决您的错误。

Answer 2

我遇到了类似的问题，当我在组合框中选择某些内容时，SelectedItem 绑定没有更新。我的问题是我必须为绑定设置 UpdateSourceTrigger=PropertyChanged。

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

Answer 3

<!-- xaml code-->
    <Grid>
        <ComboBox Name="cmbData"    SelectedItem="{Binding SelectedstudentInfo, Mode=OneWayToSource}" HorizontalAlignment="Left" Margin="225,150,0,0" VerticalAlignment="Top" Width="120" DisplayMemberPath="name" SelectedValuePath="id" SelectedIndex="0" />
        <Button VerticalAlignment="Center" Margin="0,0,150,0" Height="40" Width="70" Click="Button_Click">OK</Button>
    </Grid>



        //student Class
        public class Student
        {
            public  int Id { set; get; }
            public string name { set; get; }
        }

        //set 2 properties in MainWindow.xaml.cs Class
        public ObservableCollection<Student> studentInfo { set; get; }
        public Student SelectedstudentInfo { set; get; }

        //MainWindow.xaml.cs Constructor
        public MainWindow()
        {
            InitializeComponent();
            bindCombo();
            this.DataContext = this;
            cmbData.ItemsSource = studentInfo;

        }

        //method to bind cobobox or you can fetch data from database in MainWindow.xaml.cs
        public void bindCombo()
        {
            ObservableCollection<Student> studentList = new ObservableCollection<Student>();
            studentList.Add(new Student { Id=0 ,name="==Select=="});
            studentList.Add(new Student { Id = 1, name = "zoyeb" });
            studentList.Add(new Student { Id = 2, name = "siddiq" });
            studentList.Add(new Student { Id = 3, name = "James" });

              studentInfo=studentList;

        }

        //button click to get selected student MainWindow.xaml.cs
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Student student = SelectedstudentInfo;
            if(student.Id ==0)
            {
                MessageBox.Show("select name from dropdown");
            }
            else
            {
                MessageBox.Show("Name :"+student.name + "Id :"+student.Id);
            }
        }