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Notification of a change to a computed database property in WPF

As an exercise, I decided to create a calculator for bikes in WPF. I created two private fields with setters that trigger OnPropertyChanged(), but I have one databound property ratio, which behaves like readonly, because it is dynamically computed. When I run the program, the text fields are displayed, the initial values ​​are displayed correctly, the "working" word is displayed in the handler with the changed property, but the text block is rationot updated.

I suspect that this is due to the way the "getted" property is interesting, it would be absolutely necessary to add a personal field for everyone, I wonder if there should be some DependencyProperty in this ... But actually I have reached my limit of knowledge about this and cannot make this trivial program work.

This is my model:

class SingleGearsetModel : INotifyPropertyChanged
{
    public SingleGearsetModel()
    {
        crank = 44;
        cog = 16;
    }

    private int _crank;
    private int _cog;

    public int crank { 
        get{return _crank;}
        set{
            _crank = value;
            OnPropertyChanged("crank");
        }
    }

    public int cog {
        get{return _cog;}
        set{
            _cog = value;
            OnPropertyChanged("cog");
        } 
    }

    public double ratio
    {
        get {
            return (double)crank / (double)cog;
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string arg)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(arg));
            Console.Writeline("working");
        }
    }

} // end class

This is my XAML:

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="CalculadorFixaWPF.MainWindow"
    x:Name="Window"
    Title="MainWindow"
    Width="640" Height="480">

    <DockPanel x:Name="LayoutRoot">
            <TextBox Text="{Binding crank, Mode=TwoWay}"/>
            <TextBox Text="{Binding cog, Mode=TwoWay}"/>
            <TextBlock Text="{Binding ratio, StringFormat={}{0:0.00}}"/>
    </DockPanel>
</Window>

And this is in my code (MainWindow.xaml.cs):

public partial class MainWindow : Window
{
    public MainWindow()
    {
        this.InitializeComponent();
        this.DataContext = new SingleGearsetModel();
    }
}

Thanks for reading!

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2 answers

Since Ratio is a computed field, you want to add a notification every time a value can change. This will happen if crankor are changed cog.

So, after you report a change in them, also report what ratiohas changed:

public int crank 
{ 
    get{return _crank;}
    set{
        _crank = value;
        OnPropertyChanged("crank");

        // *** Notify that ratio has also been changed ***
        OnPropertyChanged("ratio");
    }
}

cog.

Edit: , PropertyChanged PropertyChanged :

// Constructor
public SingleGearsetModel()
{
    ....
   PropertyChanged += SingleGearsetModel_PropertyChanged;
}

// PropertyChanged event handler
void SingleGearsetModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
        if (e.PropertyName == "cog" || e.PropertyName == "crank")
        {
            OnPropertyChanged("ratio");
        }
}

, OnPropertyChanged("ratio") - , , ( SingleGearsetModel_PropertyChanged) OnPropertyChanged("ratio")

+5

- OnPropertyChanged("ratio") crank cog. OnPropertyChanged crank cog OnPropertyChanged("ratio"), , .

+2

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