Question about INotifyPropertyChanged

Question

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Hello community!
Learning WPF isn't that easy :P

I have the following problem:

I have a Textbound which DataContext is bound to a "DVD"-instance in backcode:

DvdNameTextBox.DataContext = myDvd;

But if I change my DVD like the following:

myDvd = new Dvd("From outer space", 1978);

my Binding doesn't get updated.

Now i tried to put myDvd into a class called MainWindowData, which i made INotifyPropertyChanged and tried to set the DataContext to

myData.myDvd

...Still no update.

Now i found out if i set the DataContext to

myData

and the Binding to

Text="myDvd.Name"

that the text gets updated because my PropertyChangedEventHandler isn't null anymore (I think because I used myData as DataContext)

Would have been there an more easy way to achieve data binding? I just want to get my DVDs name and have to change to DVD instance in backcode.

Thanks for your help and sorry for the long question :)

--------------------------------
--------------------------------
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IMPROVE QUESTION:

I have in MainWindowData:

private Mix selectedDVD = null;

C#

public Mix SelectedDVD
{
  get { return selectedDVD; }
  set
  {
    selectedDVD = value;
    NotifyPropertyChanged("SelectedDVD");
  }
}

On WindowLoaded I do:

MixNameTextBox.DataContext = Data.SelectedDVD;

My XAML looks the following:

C#

<TextBlock Name="DVDNameTextBox" VerticalAlignment="Center" Text="{Binding Name, Converter={StaticResource ReplaceNullStringConverter},ConverterParameter='No DVD selected'}" ></TextBlock>

And on ListBox.SelectionChanged (the ListBox to select the DVD):

C#

Data.SelectedDVD = (DVD)e.AddedItems[0];

And on this line there is the problem: The program doesn't mind that the source was changed.
It doesn't change anything to implement INotifyPropertyChange on MyWindowData and/or on DVD.

Why doesn't my Textbox realise that it has a new DataSource?

Thanks!

Posted 22-Jun-12 3:46am

NeonMika

Updated 22-Jun-12 21:32pm

v2

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3 solutions

Solution 1

It looks like what you want to do is two-way binding. Here is a Code Project article that should help clear up your questions:

Simple WPF databinding (with some additional WPF goodies)[^]

Posted 22-Jun-12 3:49am

Tim Corey

Comments

NeonMika 23-Jun-12 3:30am

No, i don't need two-way-binding, I just want to presentate my value TO the GUI without changes to make.

I have in MainWindowData:

private Mix selectedDVD = null;
public Mix SelectedDVD
{
get { return selectedDVD; }
set
{
selectedDVD = value;
NotifyPropertyChanged("SelectedDVD");
}
}

On WindowLoaded I do:

MixNameTextBox.DataContext = Data.SelectedDVD;

My XAML looks the following:
<textblock name="DVDNameTextBox" verticalalignment="Center" text="{Binding Name, Converter={StaticResource ReplaceNullStringConverter},ConverterParameter='No mix selected'}">

And on ListBox.SelectionChanged (the ListBox to select the DVD):
Data.SelectedDVD = (DVD)e.AddedItems[0];

And on this line there is the problem: The program doesn't mind that the source was changed.
It doesn't change anything to implement INotifyPropertyChange on MyWindowData and/or on DVD.

Why doesn't my Textbox realise that it has a new DataSource?

Thanks!

Solution 2

The DataContext should be set to MyDvd

For assigning Text="Name"

<textbox datacontext="MyDvd" text="{Binding Name, Mode = TwoWay}">

This works 100%

Posted 22-Jun-12 4:31am

kishhr

Comments

NeonMika 23-Jun-12 3:37am

It works if my DataContext is never changed.
The problem is, that not a Property is changed, the problem is, that the whole DataContext gets changed and this is not recognized for some reason.

Thanks.

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Amir Mahfoozi · Accepted Answer · 2012-06-23T03:21:00

Hi,
The problem is that your SelectedDVD is not a dependency property. When you bind to the Name property you are not notified of its value changes. So you should either make Name into a Dependency Property or The whole SelectedDVD object into a dependency property.

Here is a working example that I have changed the whole SelectedDVD into a dependency property (Also I have changed its name to Mix) :

C#

public partial class CPTest1 : Window
{
    public static readonly DependencyProperty MixProperty =
        DependencyProperty.Register("Mix", typeof (Mix), typeof (CPTest1), new PropertyMetadata(default(Mix)));

    public Mix Mix
    {
        get { return (Mix) GetValue(MixProperty); }
        set { SetValue(MixProperty, value); }
    }

    public CPTest1()
    {
        InitializeComponent();

        Mix = new Mix("Film 1", 2009);

        DVDNameTextBox.DataContext = this;
    }

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        Mix = new Mix("Film 2", 2011);
    }

}

public class Mix
{
    public Mix(string name, int year)
    {
        Name = name;
        Year = year;
    }

    public string Name { get; set; }
    public int Year { get; set; }
}

And the XAML part :

XML

<TextBlock Name="DVDNameTextBox" VerticalAlignment="Center" Text="{Binding Path=Mix.Name}" ></TextBlock>
<Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="178,42,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />

For creating dependency properties you can use Intelisense for getting assistance.

Good Luck.