Using propertyChanged in wpf, binding should update on button click

Question

I have created a errorMessage as a string in my ViewModel. When you get an error or stuff like that, I will use this one to display a message to the user.

In ViewModel

I have implemented the INotifyPropertyChanged interface, also I have created this block:

#region INotifyPropertyChanged members
    public event PropertyChangedEventHandler PropertyChanged;

    protected void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    #endregion

In top of the ViewModel, I have created a string called ErrorMessage.

public string ErrorMessage { get; set; }

In the constructor, I have tested it with

 ErrorMessage = "Error message";

And I can see the text in my view on load. The problem is when I hit an exception like in a try / catch block and sets the error to a text, it wont get updated.

In the Exception or on a button click, I have tried entering:

ErrorMessage = "No rooms with entered settings were found";

The View

<StackPanel Margin="10, 5" Grid.Row="5" Grid.ColumnSpan="3">
        <TextBlock FontFamily="../Fonts/bold.ttf#bold" Height="40" Foreground="Red" Text="{Binding ErrorMessage, UpdateSourceTrigger=PropertyChanged}"></TextBlock>
    </StackPanel>

If you scroll to the right, you can see that I have binded ErrorMessage and given it the UpdateSourceTrigger=PropertyChanged.

What do I need, so I can in my ViewModel, set the ErrorMessage equal to a text on certain scenarios?

Have you set the DataContext of your view to your ViewModel? — ChrisF
– ChrisF, Commented Apr 17, 2016 at 19:26
You need to call NotifyPropertyChanged in the setter of the property, you can't use an Auto property. — Siderite Zackwehdex
– Siderite Zackwehdex, Commented Apr 17, 2016 at 19:30
ChrisF, yes, else it wont have worked when I set the ErrorMessage in the constructor, its after when the context is set that I want to change errorMessage based on scenario — Raaydk
– Raaydk, Commented Apr 17, 2016 at 19:33

user6174178 · Accepted Answer · 2016-04-17 19:40:21Z

1

You must call NotifyPropertyChanged("ErrorMessage") in set method. Extend your property with full get and set accessors implementation (with a private variabile) and then call notifypropertychanged in the set method after privateproperty= value line.

It's important to Notify your view when a property changes.

S

answered Apr 17, 2016 at 19:40

user6174178

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Comments

Kylo Ren · Accepted Answer · 2016-04-18 06:37:57Z

0

Change your ErrorMessage Property as:

private string errorMessage;

    public string ErrorMessage
    {
        get { return errorMessage; }
        set 
        { 
            errorMessage = value;
            NotifyPropertyChanged("ErrorMessage");
        }
    }

answered Apr 18, 2016 at 6:37

Kylo Ren

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