How to pass data between the View and the ViewModel

问题

I'm a newbie in the MVVM design patter I'm trying to create a simple app where a list of students is shown in the main window and I want the user to be able to add a new student to the list I have accomplished the binding of the observable collection where the students' data are but how can I create a new user by fetching the data from the textboxes and using them as a parameter in a command

Here is my View

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="2*"/>
        <RowDefinition Height="2*"/>
        <RowDefinition Height="2*"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto"/>
        <ColumnDefinition Width="*"/>
    </Grid.ColumnDefinitions>

    <TextBlock x:Name="NameTextBlock"
               Text="Name"
               Style="{StaticResource TextBlockTextStyle}"/>
    <TextBlock x:Name="SurnameTextBlock"
               Grid.Row="1"
               Text="Surname"
               Style="{StaticResource TextBlockTextStyle}"/>
    <TextBlock x:Name="AgeTextBlock"
               Grid.Row="2"
               Text="Age"
               Style="{StaticResource TextBlockTextStyle}"/>
    <TextBox x:Name="NameTextBox"
             Grid.Column="1"
             Style="{StaticResource TextBoxTextStyle}"/>
    <TextBox x:Name="SurnameTextBox"
             Grid.Row="1"
             Grid.Column="1"
             Style="{StaticResource TextBoxTextStyle}"/>
    <TextBox x:Name="AgeTextBox"
             Grid.Row="2"
             Grid.Column="1"
             Style="{StaticResource TextBoxTextStyle}"/>
    <ListBox x:Name="StudentListBox"
             Grid.ColumnSpan="2"
             Grid.Row="4"
             Style="{StaticResource ListBoxStyle}"
             ItemsSource="{Binding StudentList}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto"/>
                        <ColumnDefinition Width="Auto"/>
                        <ColumnDefinition Width="Auto"/>
                    </Grid.ColumnDefinitions>
                    <TextBlock Text="{Binding Name}"
                               Style="{StaticResource TextBlockTextStyle}"/>
                    <TextBlock Text="{Binding Surname}"
                               Grid.Column="1"
                               Style="{StaticResource TextBlockTextStyle}"/>
                    <TextBlock Text="{Binding Age}"
                               Grid.Column="2"
                               Style="{StaticResource TextBlockTextStyle}"/>
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
    <Button x:Name="AddButton"
            Grid.Row="7"
            Grid.ColumnSpan="2"
            HorizontalAlignment="Center"
            Content="Add"
            Margin="7,7,7,7"
            Command="{Binding AddStudentCommand}"/>        
</Grid>

And here is my ViewModel

public class MainViewModel : ViewModelBase
{
    ObservableCollection<Student> studentList;
    public MainViewModel()
    {
        //populate some sample data
        studentList = new ObservableCollection<Student>()
        {
            new Student(){Name="John", Surname="Smith", Age="28"},
            new Student(){Name="Barbara", Surname="Anderson", Age="23"}
        };
    }

    public ObservableCollection<Student> StudentList
    {
        get { return studentList; }
        set { RaisePropertyChanged("studentList"); }
    }

    Student selectedPerson;
    public Student SelectedPerson
    {
        get { return selectedPerson; }
        set
        {
            selectedPerson = value;
            RaisePropertyChanged("SelectedPerson");
        }
    }

    private RelayCommand _addStudentCommand;
    public ICommand AddStudentCommand
    {
        get
        {
            return _addStudentCommand
                ?? (_addStudentCommand = new RelayCommand(() =>
                {
                    Student student = new Student();
                    // here should be the logic of defining the name, surname, 
                    // age and id of the newly created student
                    studentList.Add(student);
                }));
        }
    }

}

I am using MVVMLight in the current project and there are a lot of thing that I do not understand so please explain how I should pass the data of the textboxes and what exactly should happen in the command that it is being used.

Tell me to add more of the code if necessary.

回答1:

What I would do is create some properties that the textboxes are bound to in the ViewModel. Like this for all three (in your viewmodel)

private string _Name;
    public string Name
    {
        get { return _Name; }
        set
        {
            _Name = value;
            RaisePropertyChanged("Name");
        }
    }

Then, in the XAML, bind the textbox's text to this:

<TextBox x:Name="NameTextBox"
             Text="{Binding Name}"
         Grid.Column="1"
         />

Finally in the AddStudent Command you reference the properties in the viewmodel that are bound to the textboxes.

private RelayCommand _addStudentCommand;
    public ICommand AddStudentCommand
    {
        get
        {
            return _addStudentCommand
                ?? (_addStudentCommand = new RelayCommand(() =>
                {
                    Student student = new Student();
                    student.Name = this.Name;
                    student.Surname = this.Surname;
                    student.Age = this.Age;
                    // here should be the logic of defining the name, surname, 
                    // age and id of the newly created student
                    _StudentList.Add(student);
                }));
        }
    }

回答2:

(cheekily posted from my comment)

As you've stated, you've not had much experience and don't understand much with MVVM, so although I could answer this question, I think the best thing I could do is provide you with a few links to watch :

youtube.com/watch?v=BClf7GZR0DQ

and

channel9.msdn.com/blogs/kreekman/

The second video is from the guy who wrote MVVM-light.

They basically cover the same material, but both bring a slightly different perspective!

来源：https://stackoverflow.com/questions/20036466/how-to-pass-data-between-the-view-and-the-viewmodel