在WPF组合框设为默认值 [英] Set default value in WPF ComboBox

问题描述

我使用的组合框ItemsSource属性绑定来显示列表项组合框。

I am using ComboBox ItemsSource property binding to display items from a List to combo box.

以下是code：

<ComboBox x:Name="Cmb_Tax" ItemsSource="{Binding TaxList}" 
            DisplayMemberPath="ChargeName" SelectedItem="{Binding 
            SelectedTax,UpdateSourceTrigger=PropertyChanged}" IsEditable="True" 
            IsTextSearchEnabled="True" SelectionChanged="Cmb_Tax_SelectionChanged"/>

Classes.Charges _selected_tax = new Classes.Charges();
public Classes.Charges SelectedTax
{
    get
    {
        return _selected_tax;
    }
    set
    {
        _selected_tax = value;
    }
}

List<Classes.Charges> _taxlist = new List<Classes.Charges>();
public List<Classes.Charges> TaxList
{
    get
    {
        return _taxlist;
    }
    set
    {
        _taxlist = value;
        OnPropertyChanged("TaxList");
    }
}

它正确地显示在组合框中的项目。

It displays the items in the combo box correctly.

有一个在TaxList一个特定的项目无税，我想在默认情况下，在组合框中选择。此产品可present在列表（列表中没有必要的第一个或最后一个项目）任何指数。

There is a particular item in TaxList "No Tax" which I want to be selected by default in the combo box. This item can be present at any index in the list (Not necessary first or last item of the list).

我尝试使用下面的code的组合框中选定的索引属性设置，但遗憾的是它不工作。

I am trying to use the following code to set the selected index property of combo box, but sadly its not working.

TaxList = Classes.Charges.GetChargeList("Tax");
Cmb_Tax.DataContext = this;            
int i = TaxList.FindIndex(x => x.ChargeName == tax_name);
Cmb_Tax.SelectedIndex = i;

该方法FindIndex（）返回的无税正确索引，但是当我尝试将其分配给的SelectedIndex 组合的的SelectedIndex 不会改变。它保持在-1。

The Method FindIndex() returns the index of the "No Tax" correctly but when I try assigning it to SelectedIndex of combo the SelectedIndex doesn't change. It stays at -1.

UPDATE1

private void Cmb_Tax_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    MessageBox.Show(SelectedTax.ChargeName);
}

UPDATE2 更新了code按建议的@ElectricRouge

Update2 Updated the code as per suggested by @ElectricRouge

<ComboBox x:Name="Cmb_Tax" ItemsSource="{Binding TaxList, Mode=TwoWay}" 
                      DisplayMemberPath="ChargeName" SelectedItem="{Binding SelectedTax,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"
                      IsEditable="True" IsTextSearchEnabled="True" 
                      SelectionChanged="Cmb_Tax_SelectionChanged"/>


Classes.Charges _selected_tax = new Classes.Charges();
        public Classes.Charges SelectedTax
        {
            get
            {
                return _selected_tax;
            }
            set
            {
                _selected_tax = value;
                OnPropertyChanged("SelectedTax");
            }
        }

        ObservableCollection<Classes.Charges> _taxlist = new ObservableCollection<Classes.Charges>();
        public ObservableCollection<Classes.Charges> TaxList
        {
            get
            {
                return _taxlist;
            }
            set
            {
                _taxlist = value;
                OnPropertyChanged("TaxList");
            }
        }

public void Load_Tax(string tax_name = null, Classes.Charges selected_tax = null)
        {
            TaxList = Classes.Charges.GetParticularChargeList("Tax");
            Cmb_Tax.DataContext = this;
            //Cmb_Tax.SelectedValue = tax_name;
            SelectedTax = selected_tax;
            //int i = TaxList.FindIndex(x => x.ChargeName == tax_name);
            //Cmb_Tax.SelectedIndex = i;
        }

任何想法，为什么这必须是这样吗？ 也请提出任何其他的方法来显示默认的组合框。

Any idea why this must be happening? Also please suggest any other approach to display default in combo box.

推荐答案

下面是一个工作示例：

视图模型：

 public MainWindow()
    {
        InitializeComponent();

        var vm = new ViewModel();
        this.DataContext = vm;
        this.Loaded += (o,e) => vm.LoadData();
    }

    public class ViewModel : INotifyPropertyChanged
    {
        private IList<Charges> taxList;
        public ICollectionView TaxList { get; private set; }

        public void LoadData()
        {                
            taxList = Charges.GetChargeList("taxes");

            TaxList = CollectionViewSource.GetDefaultView(taxList);
            RaisePropertyChanged("TaxList");

            TaxList.CurrentChanged += TaxList_CurrentChanged;              

            var noTax = taxList.FirstOrDefault(c => c.ChargeName == "No Tax");
            TaxList.MoveCurrentTo(noTax);
        }

        void TaxList_CurrentChanged(object sender, EventArgs e)
        {
            var currentCharge = TaxList.CurrentItem as Charges;
            if(currentCharge != null)
                MessageBox.Show(currentCharge.ChargeName);
        }



        public event PropertyChangedEventHandler PropertyChanged;
        public void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}

查看：

<ComboBox x:Name="cboTaxList" 
              ItemsSource="{Binding TaxList}" 
              DisplayMemberPath="ChargeName"
              IsSynchronizedWithCurrentItem="True" />

这篇关于在WPF组合框设为默认值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！