如何使用 MVVM 架构在 WPF 中设置组合框值答案

【问题标题】：How to set combo box value in WPF using MVVM architecture如何使用 MVVM 架构在 WPF 中设置组合框值
【发布时间】：2020-05-20 05:45:27
【问题描述】：

我在 WPF MVVM 架构中创建了一个 POC。我在其中使用了组合框控件，您可以在下面的代码中看到。

 <ComboBox Name="DeptCombo" Grid.Row="4" Grid.Column="1" ItemsSource="{Binding DepartmentList,Mode=TwoWay}" SelectedItem="{Binding Path=CurrentDepartment,Mode=TwoWay}" DisplayMemberPath="DepartmentName">
</ComboBox>

这里 CurrentDepartment 是 Department 类的一个属性。

一切都很好，我填充了该组合，将该组合值保存在数据库中，但我面临的唯一问题是，我无法在该组合中设置保存的数据库值。我没有得到任何解决方案关于那个。请帮助我。

【问题讨论】：

标签： c# mvvm combobox wpf-controls

【解决方案1】：

添加UpdateSourceTrigger

  SelectedItem="{Binding Path=CurrentDepartment,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"

他的代码应该是这样的：

  class ViewModel: INotifyPropertyChanged
{
    public ObservableCollection<string> Datas { get; set; } = new ObservableCollection<string>()
    {
        "FF", "AA", "BB"
    };

    private string currentItem;
    public string CurrentItem
    {
        get => currentItem;
        set
        {
            currentItem = value;
            OnPropertyChanged("CurrentItem");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    public void OnPropertyChanged([CallerMemberName]string prop="")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(prop));
    }
}

型号示例： PersonModel.cs：

   class PersonModel
{
    public string Name { get; set; }
    public int Age { get; set; }
}

ViewModel.cs：

 class ViewModel: INotifyPropertyChanged
    {
        public ObservableCollection<PersonModel> Datas { get; set; } = new ObservableCollection<PersonModel>()
        {
            new PersonModel(){Age = 10, Name="Tom"},
            new PersonModel(){Age = 10, Name="Mark"},
        };

        private PersonModel currentItem;
        public PersonModel CurrentItem
        {
            get => currentItem;
            set
            {
                currentItem = value;
                OnPropertyChanged("CurrentItem");
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged([CallerMemberName]string prop="")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(prop));
        }
    }

MainWindow.xaml：

 <ComboBox ItemsSource="{Binding Datas}" SelectedItem="{Binding CurrentItem, UpdateSourceTrigger=PropertyChanged}"
              Height="100" Width="100">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <StackPanel>
                    <TextBlock Text="{Binding Name}"/>
                    <TextBlock Text="{Binding Age}"/>
                </StackPanel>
            </DataTemplate>
        </ComboBox.ItemTemplate>
    </ComboBox>

【讨论】：

嗨@典型请详细解释您的解决方案为什么我在这里使用 UpdateSourceTrigger
@Shubham，当 ViewModel CurrentDepartment 发生变化时，它需要更新您的 ComboBox 属性。 UpdateSourceTrigger 旨在设置更新数据的逻辑。
它不起作用我需要在视图模型中添加更多关于 PropertyChanged 的内容
@Shubham，我在回复中添加了一个示例
完美@典型，当我在组合中绑定字符串类型变量列表时它工作正常，但是当我使用类类型对象列表时，问题就出现了，在我的情况下 ItemsSource="{Binding DepartmentList,Mode=TwoWay}" 这里Department list是Department类的列表，SelectedItem="{Binding path=CurrentDepartment,Mode=TwoWay}" 这里CurrentDepartment是Department类的属性

【解决方案2】：

部门类：

 public class Department : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertychanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    private int id;
    public int Id
    {
        get { return id; }
        set { id = value; OnPropertychanged("Id"); }
    }

    private string departmentName;
    public string DepartmentName
    {
        get { return departmentName; }
        set { departmentName = value; OnPropertychanged("DepartmentName"); }
    }

    private bool isActive;
    public bool IsActive
    {
        get { return isActive; }
        set { isActive = value; OnPropertychanged("IsActive"); }
    }
}

查看模型：

private ObservableCollection<Department> departmentList;
    public ObservableCollection<Department> DepartmentList
    {
        get { return departmentList; }
        set { departmentList = value; OnPropertyChanged("DepartmentList"); }
    }

 private Department currentDepartment;
    public Department CurrentDepartment
    {
        get { return currentDepartment; }
        set { currentDepartment = value; OnPropertyChanged("CurrentDepartment"); }
    }

 private void DepartmentPop()
    {
        DepartmentList = new ObservableCollection<Department> 
                (objDepartmentService.GetAll());
    }

【讨论】：