Question

我不确定bind对combobox control view model的正确方法是什么。

我正在使用MVVM方法，所以在我的viewmodel我正在加载所有CDType数据，并将其源与实际记录属性model.CDType.id和{{绑定在一起1}}。

当我更改文本时会发生什么？ - 我保留旧ID（来自加载例程）并从组合框绑定中获取新文本值，因此总是在现有记录上写入创建一个新的。

如果文本不在列表中，如何让我的组合框将id设置为0 / undefined？（手动？ - 有点蹩脚）

一切都会有所帮助 - 谢谢！

TL; DR：可编辑的组合框不会在文本更改时更新ID。

示例Xaml绑定：

model.CDType.name

Answer 1

我可以理解，当手动更改所选ComboBox项的名称时，您需要更新上一个最后选择的值，并且此名称未显示在ComboBox ItemSource中。这是我的建议，它是您的ComboBox控件数据绑定和ViewModel中定义的逻辑的组合。

绑定说明

由于ComboBox ItemsSource是Cd（ComboModels的集合）的集合，因此TextSearch.TextPath绑定应定义为CDType.Name，其中CdType是在描述子模型的ComboModel中定义的属性，并且名称是描述子模型的实际搜索路径。
ComboBox Text属性绑定到AssignmentText属性，以在组合丢失焦点时触发更新逻辑（如绑定中所定义）。
您的示例代码中定义的ItemsSource是微不足道的。
选定的值将使整个模型更新（如果我们更改所选的值名称）。
由于ComboBox ItemsSource是Cd的集合（我们称之为ComboModel），DisplayMemberPath绑定应定义为CDType.Name，其中CdType是描述子模型的ComboModel中定义的属性，名称是描述子模型的实际搜索路径。

Xaml代码：

        <Grid VerticalAlignment="Bottom">
        <Grid.DataContext>
            <comboBoxWhenNoAnySelectedHelpAttempt:ComboboxDataContext/>
        </Grid.DataContext>
        <StackPanel Orientation="Vertical">
            <ComboBox x:Name="ddlCDType"    
                      IsTextSearchEnabled="True"     
                      IsTextSearchCaseSensitive="False"     
                      StaysOpenOnEdit="True"    
                      TextSearch.TextPath="CDType.Name"
                      Text="{Binding AssignmentText,     
                      UpdateSourceTrigger=LostFocus, Mode=TwoWay,
                      ValidatesOnDataErrors=True}"
                      ItemsSource="{Binding CDTypes}"    
                      SelectedValue="{Binding Assignment}"     
                      DisplayMemberPath="CDType.Name"     
                      IsEditable="True"     
                      HorizontalAlignment="Left"     
                      Margin="98,10,0,0"     
                      VerticalAlignment="Top"     
                      Width="136" />
            <!--added to see changes in updated combo box item-->
            <TextBlock >
                      <Run Text="Name:"/>
                      <Run Text="{Binding Assignment.CDType.Name, UpdateSourceTrigger=PropertyChanged}"></Run>
                      <Run Text="Id:"/>
                      <Run Text="{Binding Assignment.CDType.ID, UpdateSourceTrigger=PropertyChanged}"></Run>
            </TextBlock>
        </StackPanel>
    </Grid>

虚拟机代码

public class ComboboxDataContext:BaseObservableObject
{
    private ObservableCollection<ComboModel> _cdTypes;
    private ComboModel _assignment;
    private string _assignmentText;
    private string _lastAcceptedName;


    public ComboboxDataContext()
    {
        CDTypes = new ObservableCollection<ComboModel>
        {
            new ComboModel
            {
                CDType = new ComboModelSubModel
                {
                    Name = "Cd-1",
                    ID = "1",
                },
            },
            new ComboModel
            {
                CDType = new ComboModelSubModel
                {
                    Name = "Cd-2",
                    ID = "2",
                }
            },
            new ComboModel
            {
                CDType = new ComboModelSubModel
                {
                    Name = "Cd-3",
                    ID = "3",
                },
            },
            new ComboModel
            {
                CDType = new ComboModelSubModel
                {
                    Name = "Cd-4",
                    ID = "4",
                }
            }
        };
        Assignment = CDTypes.FirstOrDefault();
    }

    public ObservableCollection<ComboModel> CDTypes
    {
        get { return _cdTypes; }
        set
        {
            _cdTypes = value;
            OnPropertyChanged();
        }
    }

    public ComboModel Assignment
    {
        get { return _assignment; }
        set
        {
            if (value == null)
                _lastAcceptedName = _assignment.CDType.Name;
            _assignment = value;
            OnPropertyChanged();
        }
    }

    //on lost focus when edit is done will check and update the last edited value
    public string AssignmentText
    {
        get { return _assignmentText; }
        set
        {
            _assignmentText = value;
            OnPropertyChanged();
            UpDateSourceCollection(AssignmentText);
        }
    }

    //will do the the update on combo lost focus to prevent the 
    //annessasary updates (each property change will make a lot of noice in combo)
    private void UpDateSourceCollection(string assignmentText)
    {
        var existingModel = CDTypes.FirstOrDefault(model => model.CDType.Name == assignmentText);
        if (existingModel != null) return;
        if (_lastAcceptedName == null)
        {
            CDTypes.Add(new ComboModel{CDType = new ComboModelSubModel{ID = string.Empty, Name = assignmentText}});
        }
        else
        {
            var existingModelToEdit = CDTypes.FirstOrDefault(model => model.CDType.Name == _lastAcceptedName);
            if(existingModelToEdit == null) return;
            existingModelToEdit.CDType.Name = assignmentText;
            existingModelToEdit.CDType.ID = string.Empty;
        }

    }
}

public class ComboModel:BaseObservableObject
{
    private ComboModelSubModel _cdType;

    public ComboModelSubModel CDType
    {
        get { return _cdType; }
        set
        {
            _cdType = value;
            OnPropertyChanged();
        }
    }
}

public class ComboModelSubModel:BaseObservableObject
{
    private string _id;
    private string _name;

    public string ID
    {
        get { return _id; }
        set
        {
            _id = value;
            OnPropertyChanged();
        }
    }

    public string Name
    {
        get { return _name; }
        set
        {
            _name = value;
            OnPropertyChanged();
        }
    }
}

BaseObservableObject代码

    /// <summary>`enter code here`
/// implements the INotifyPropertyChanged (.net 4.5)
/// </summary>
public class BaseObservableObject : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual void OnPropertyChanged<T>(Expression<Func<T>> raiser)
    {
        var propName = ((MemberExpression)raiser.Body).Member.Name;
        OnPropertyChanged(propName);
    }

    protected bool Set<T>(ref T field, T value, [CallerMemberName] string name = null)
    {
        if (!EqualityComparer<T>.Default.Equals(field, value))
        {
            field = value;
            OnPropertyChanged(name);
            return true;
        }
        return false;
    }
}

问候。

WPF绑定可编辑组合框不更改文本更改时的ID

1 个答案: