WPF - MVVM 绑定答案

【问题标题】：WPF - MVVM BindingsWPF - MVVM 绑定
【发布时间】：2017-03-03 12:35:19
【问题描述】：

我的应用程序有问题，尤其是 WPF MVVM 中的绑定。我创建了模型、视图模型和视图，这是我的代码的一部分（仅与我的问题有关）当我单击按钮 nemed : PointUp 我想查看 Team1 点的数量。谁能告诉我我做错了什么？

查看

    <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>

型号

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; }
    }
}

视图模型

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(); }
    }
}

【问题讨论】：

标签： c# wpf mvvm

【解决方案1】：

问题出在这里：

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

在ViewModel 中的TeamPoints 属性中，您返回并从ViewModel 设置相同的属性TeamPoints，但您应该从Model (Team1) 设置。你应该返回并设置Team1.TeamPoints。

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

还有Add_Points()：

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

【讨论】：

【解决方案2】：

你必须像这样更新你的绑定。

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

当您绑定到 Team1.TeamPoints 时，您将不会从 TeamPoints 属性内的 OnPropertyChanged 获得通知。

【讨论】：

是的，这是真的，我的错误 :) 它有效，但只是在开始时，点数仍然是相同的 exual 0。绑定不刷新
啊，好的，我明白了。您在 AddTeamPoints 方法中更新 Team1.Teampoints，NotifyPropertyChanged 将不会再次触发。当你写 OnPropertyChanged("TeamPoints"); Team1.TeamPoints++ 之后；会好的。
谢谢！我没注意到。

【解决方案3】：

我认为这是因为 AddPoints（命令绑定）。由于此命令已绑定并且您正在创建 RelayCommand 的实例并在每次它可能破坏绑定时返回。

CommandBindings 的更好替代方法是声明属性并在视图模型的构造函数中初始化它们。

例如：

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));
        }
    }
}

【讨论】：