What's wrong with my WPF Binding (in C# code)?

Question

I didnt use WPF for a long time so I'm quite sure this is an easy question for most of you but here is my xaml code :

<Grid>
    <ProgressBar Name="Progress" Width="200" Height="20" Minimum="0" Maximum="100" Margin="10"/>
</Grid>

and here is the C# code :

namespace WpfApplication1
{
    public partial class MainWindow : Window, INotifyPropertyChanged
    {
        private int _MyInt;
        public int MyInt
        {
            get { return _MyInt; }
            set
            {
                _MyInt = value;
                RaisePropertyChanged("MyInt");
            }
        }

        public MainWindow()
        {
            InitializeComponent();

            MyInt = 99;

            Random random = new Random();
            System.Timers.Timer aTimer = new System.Timers.Timer();
            aTimer.Elapsed += (sender, e) =>
            {
                MyInt = random.Next(0, 100);
            };
            aTimer.Interval = 500;
            aTimer.Enabled = true;

            Binding b = new Binding();
            b.Source = MyInt;
            b.Mode = BindingMode.OneWay;
            Progress.SetBinding(ProgressBar.ValueProperty, b);
        }
        public event PropertyChangedEventHandler PropertyChanged;
        public void RaisePropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
                handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

When the application starts I got a 99 value on my ProgressBar so the binding seems to work but then, it doesn't refresh at all...

Progress.Value = MyInt; should do it no ? I tried with an ItemSource of a ListBox and it worked — Guillaume Slashy
– Guillaume Slashy, Commented Dec 1, 2011 at 14:33
take a look at this: stackoverflow.com/questions/2368479/wpf-data-binding-with-code — N_A
– N_A, Commented Dec 1, 2011 at 14:34
I know I can do a Binding "manually" but can't I but it this way ? (like in my code snippet) — Guillaume Slashy
– Guillaume Slashy, Commented Dec 1, 2011 at 14:36
All your snippet is doing is assigning a value to the value of your control. You need to explicitly set the binding for it to work (either in xaml or in the code) — N_A
– N_A, Commented Dec 1, 2011 at 14:44

Rachel · Accepted Answer · 2011-12-01 15:27:15Z

3

Progress.Value = MyInt is simply setting the value to whatever the current value in MyInt is. This is not the same as binding the value, which means the value will point to MyInt, not be a copy of MyInt

To create a binding in the code-behind, it would look something like this:

Binding b = new Binding();
b.Source = this;
b.Path = new PropertyPath("MyInt");
Progress.SetBinding(ProgressBar.ValueProperty, b);

An alternative is to just bind the value in your XAML and update it as needed:

<ProgressBar Name="Progress" Value="{Binding MyInt}" />

Then in the code behind: MyInt = newValue;

edited Dec 1, 2011 at 15:27

answered Dec 1, 2011 at 14:40

Rachel

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16 Comments

Guillaume Slashy Over a year ago

Code this strange error : Member System.Windows.Controls.Primitives.RangeBase.ValueProperty' cannot be accessed with an instance reference; qualify it with a type name instead

Rachel Over a year ago

@GuillaumeCogranne Sorry, the binding needs to reference the ProgressBar class, not your ProgressBar Instance. I updated my answer

Guillaume Slashy Over a year ago

I got this error with ur new version : {"'The invocation of the constructor on type 'WpfApplication1.MainWindow' that matches the specified binding constraints threw an exception.' Line number '3' and line position '9'."}

Guillaume Slashy Over a year ago

If I comment the line "Progress.SetBinding(ProgressBar.ValueProperty, myBinding);" I got no more error but the binding doesnt work ofc.. !

Guillaume Slashy Over a year ago

And I got the same error if I try to bind in the xaml file :( Dunno if this has to do with the Timer im using

|

MBen · Accepted Answer · 2011-12-01 14:40:23Z

0

First, I don't think your window should be implementing the INotifyPropertyChanged. You are putting the data in your Window. You should have a separate class that implements INotifyPropertyChanged, and then set it as a DataContext to your Window. After that you need to add a Binding either through code, or in XAml like this :

<ProgressBar Name="Progress" Width="200" Height="20" Minimum="0" Maximum="100" Margin="10" Value="67" Value="{Binding MyInt}"/>

answered Dec 1, 2011 at 14:40

MBen

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9 Comments

Guillaume Slashy Over a year ago

I'm not sure about the necessity of INotifyPropertyChanged but the thing is that I'd like to code the binding in C# code (not xaml) !

N_A Over a year ago

INotifyPropertyChanged is typically used on the view model not on a view. Since you have code in your view code-behind, that doesn't really fit the architecture you're using.

MBen Over a year ago

Rachel posted the code needed to create Binding in C#. BUt you still need to INotifyPropertyChanged, since WPF can't know when you values change, unless it checks it everytime, very suboptimal, we need to let it know that something changed.

MBen Over a year ago

@mydogisbox even if it is in the Window, WPF has no way to know that the values changed, unless he calls Progress.Value = MyInt; everytime MyInt changes

MBen Over a year ago

and it that case Binding is useless

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