WPF - MVVM绑定

Question

I have problem with my application, especially with Bindings in WPF MVVM. I created Model, ViewModel and View, this is part of my code (only this connected with my problem) When I click the button nemed : PointUp i want to see the amount of Team1 points. Can anyone tell me what i'm doing wrong?

View

    <Window x:Class="Tabu.Game
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Tabu"
        xmlns:vm="clr-namespace:Tabu.ViewModel"
        mc:Ignorable="d"
        Title="Game"  Height="600" Width="900" Background="Beige">
    <Window.DataContext>
        <vm:TeamStatistic />
    </Window.DataContext>
    <Grid>
        <Button x:Name="PointUp" Command="{Binding AddPoints }" Content="+"/>
        <Label x:Name="PointsTeam1_label" Content="{Binding Team1.TeamPoints, UpdateSourceTrigger=PropertyChanged }"/>
</Grid>

Model

'

namespace Tabu.Model
{
    public class Team
    {
        public bool IsTeamActive { get;  set; }
        public int TeamMiss { get;  set; }
        public int TeamPoints { get;  set; }
        public int TeamMistake { get;  set; }
    }
}

'

ViewModel

 namespace Tabu.ViewModel { class TeamStatistic : INotifyPropertyChanged { public Team Team1 = new Team(); public int TeamPoints { get { return TeamPoints; } set { TeamPoints = value; OnPropertyChanged("TeamPoints"); } } public ICommand AddPoints { get { return new RelayCommand(() => Add_Points()); } } public void Add_Points() { Team1.TeamPoints++; } public event PropertyChangedEventHandler PropertyChanged; private void OnPropertyChanged(params string[] propsName) { if (PropertyChanged!=null) { foreach(string propName in propsName) PropertyChanged(this, new PropertyChangedEventArgs(propName)); } } } public class RelayCommand : ICommand { private readonly Func<bool> canExecute; private readonly Action execute; public RelayCommand(Action execute) : this(execute, null) { } public RelayCommand(Action execute, Func<bool> canExecute) { if (execute == null) throw new ArgumentNullException("execute"); this.execute = execute; this.canExecute = canExecute; } public event EventHandler CanExecuteChanged { add { if (this.canExecute != null) CommandManager.RequerySuggested += value; } remove { if (this.canExecute != null) CommandManager.RequerySuggested -= value; } } public Boolean CanExecute(object parameter) { return this.canExecute == null ? true : this.canExecute(); } public void Execute(object parameter) { this.execute(); } } } 

Answer 1

The problem is here:

public int TeamPoints
{
    get { return TeamPoints; } //should be Team1.TeamPoints
    set { TeamPoints = value; OnPropertyChanged("TeamPoints"); } //should be Team1.TeamPoints
}

Inside your TeamPoints property in ViewModel you return and set the same property TeamPoints from ViewModel but you should set from Model ( Team1 ). You should return and set Team1.TeamPoints .

public int TeamPoints
{
    get { return Team1.TeamPoints; }  
    set { Team1.TeamPoints = value; OnPropertyChanged("TeamPoints"); }
}

And Add_Points() :

public void Add_Points()
{
    Team1.TeamPoints++;
    OnPropertyChanged("TeamPoints");
}

Answer 2

You have to update your Binding like this.

<Label x:Name="PointsTeam1_label" Content="{Binding TeamPoints, UpdateSourceTrigger=PropertyChanged }"/>

When you bind to Team1.TeamPoints you will not get the Notification from OnPropertyChanged which is inside your TeamPoints property.

Answer 3

I reckon it is because of AddPoints (the command binding). Since this command is binded & you are creating an instance of RelayCommand & returning each time it might be breaking the binding.

A better alternative with CommandBindings are to declare the property and initialize them in the Constructor of the view model.

Ex:

namespace Tabu.ViewModel
{
  class TeamStatistic : INotifyPropertyChanged

  {
    public Team Team1 = new Team();

    public int TeamPoints
    {
        get { return Team1.TeamPoints; }
        set { Team1.TeamPoints = value; OnPropertyChanged("TeamPoints"); }
    }

    private ICommand _AddPoints;

    public ICommand AddPoints
    {
        get { return _AddPoints; }
        set { _AddPoints = value; }
    }

    public void Add_Points()
    {
        Team1.TeamPoints++;
    }

    public TeamStatistic ()
    {
        _AddPoinss = new RelayCommand(Add_Points);
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(params string[] propsName)
    {
        if (PropertyChanged!=null)
        {
            foreach(string propName in propsName)
            PropertyChanged(this, new PropertyChangedEventArgs(propName));
        }
    }
}