CODEWITHSUNDEEP
c#wpfmvvm
nichu09
nichu09

Reputation: 892

In mvvm the view doesn't update

i am beginner in mvvm concept.so i tried one sample application.it contains two textbox are name and id, one submit button,one label.when i click submit button it combine the two strings from the textbox and display in label.

i can submit the values and in viewmodel the property contain the result.but its not shown in view.why..?

in view contains

<grid>
<TextBox Grid.Column="1" Grid.Row="1" Text="{Binding name}"  Height="23"  Margin="9" Name="txtname"  Width="120" />
<TextBox Grid.Column="1" Grid.Row="2" Text="{Binding id}" Height="23"  Margin="9" Name="txtid"  Width="120" />
<Button Command="{Binding submit}" Content="submit" Grid.Column="2" Grid.Row="2" Height="23"   Name="btnsubmit"  Width="75" />
<Label Content="{Binding display}" Grid.Row="3" Height="38" HorizontalAlignment="Left"  Name="lbldisplay"  Width="192" />

</grid>

view.cs code is

public MainWindow()
    {
        InitializeComponent();
        DataContext = new DemoViewModel();
    }

in my viewmodel contains two .cs file

one is DemoViewModelInotify.cs.in this i write the code for inotifypropertychanged. another one is DemoViewModel.cs.this contain the property and commands.

namespace mvvmdemonixon.ViewModel
{
public  class DemoViewModel :DemoViewModelInotify
{
  public ICommand submit { get; set; }

  public string name { get; set; }
  public string display { get; set; }
  public int id{get;set;}
  public DemoModel model { get; set; }
  public DemoViewModel()
  {

      submit = new DelegateCommand<object>(this.add);

  }

  public void add(object paramter)
  {
    string a=  mvvmdemonixon.Model.DemoModel.addstring(name, id);
    display = a;
  }

}
}

my model contains

namespace mvvmdemonixon.Model
{
public  class DemoModel
{
   public static string addstring(string name1, int no1)
   {
       string display = "The Student Name Is " + name1 + "and Id Is" + no1 + ".";
       return display;
   }

}
}

in my app.xaml.cs

private void OnStartup(object sender, StartupEventArgs e)
    {
        mvvmdemonixon.MainWindow view = new MainWindow();
        view.DataContext = new mvvmdemonixon.ViewModel.DemoViewModel();
        view.Show();
    }

in my app xaml

<Application x:Class="mvvmdemonixon.App"
Startup="OnStartup">
</Application>

advance thanks..

Upvotes: 0

Views: 2405

Answers (3)

Ekk
Ekk

Reputation: 5715

There are two things you were missing. The first thing is your View's binding is OneTime. The second thing is you ViewModel does not notify when a property changed.

To fix the first problem, you have to update xaml like below.

<Label Content="{Binding display, Mode=OneWay}" Grid.Row="3" Height="38" HorizontalAlignment="Left"  Name="lbldisplay"  Width="192" />

To fix your second problem, you have to implement INotifyPropertyChanged.

Upvotes: 0

Dennis
Dennis

Reputation: 37790

WPF binding engine uses INotifyPropertyChanged (for scalar properties) and INotifyCollectionChanged (for collection properties) interfaces to reflect changes, which has been made in bound data source (view model).

This:

public string display { get; set; }

means, that any property setting will not notify the view, because setter's code doesn't contain any notifications. The code should be like this:

public string display 
{ 
    get { return _display; }
    set
    {
        if (_display != value)
        {
            _display = value;
            OnPropertyChanged("display");
        }
    } 
}
private string _display;

where OnPropertyChanged raises INotifyPropertyChanged.PropertyChanged event.

This is true for other view-bound properties in your view model, which should update the view.

Upvotes: 2

MichaelS
MichaelS

Reputation: 7123

You need to implement INotifyPropertyChanged in your ViewModel. And raise the property changed event from each property setter.

Upvotes: 0

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