[英]Set default value in WPF ComboBox
我正在使用ComboBox ItemsSource屬性綁定來顯示從List到組合框的項目。
以下是代碼:
<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");
}
}
它正確顯示組合框中的項目。
TaxList "No Tax"
有一個特定項目,我想在組合框中默認選擇它。 此項目可以出現在列表中的任何索引處(不必是列表中的第一個或最后一個項目)。
我試圖使用以下代碼來設置組合框的選定索引屬性,但遺憾的是它無法正常工作。
TaxList = Classes.Charges.GetChargeList("Tax");
Cmb_Tax.DataContext = this;
int i = TaxList.FindIndex(x => x.ChargeName == tax_name);
Cmb_Tax.SelectedIndex = i;
該方法FindIndex()返回的索引"No Tax"
正確,但是當我嘗試將其分配給SelectedIndex
組合的SelectedIndex
不會改變。 它保持在-1。
UPDATE1
private void Cmb_Tax_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
MessageBox.Show(SelectedTax.ChargeName);
}
Update2根據@ElectricRouge的建議更新了代碼
<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;
}
知道為什么會這樣嗎? 另外,請建議在組合框中顯示默認值的任何其他方法。
這是一個工作樣本:
視圖模型:
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));
}
}
}
}
視圖:
<ComboBox x:Name="cboTaxList"
ItemsSource="{Binding TaxList}"
DisplayMemberPath="ChargeName"
IsSynchronizedWithCurrentItem="True" />
List沒有實現INotifyCollectionChanged
使其成為ObservableCollection
ObservableCollection<Classes.Charges> _taxlist = new ObservableCollection<Classes.Charges>();
public ObservableCollection<Classes.Charges> TaxList
{
get
{
return _taxlist;
}
set
{
_taxlist = value;
OnPropertyChanged("TaxList");
}
}
並嘗試設置Mode = TwoWay
SelectedItem="{Binding SelectedTax,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"
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