Question

我有如下所述的课程结构。

 //On the design aspects, I know It may not be the advisable approach, 
 //but something of this kind is only required.

/// <summary>
/// Paper Class
/// </summary>
public class Paper
{
    public string PaperName { get; set; }
    public bool IsPending { get; set; }
}

/// <summary>
/// PaperChecking class, Individual papers will be processed here.
/// </summary>
public class PaperChecking
{

    public static List<Paper> ListPapers { get; set; }

    public static void AddPapers()
    {
        ListPapers = new List<Paper>();

        ListPapers.Add(new Paper() { PaperName = "Paper1", IsPending = false });
        ListPapers.Add(new Paper() { PaperName = "Paper2", IsPending = false });
        ListPapers.Add(new Paper() { PaperName = "Paper3", IsPending = false });
        ListPapers.Add(new Paper() { PaperName = "Paper4", IsPending = false });
        ListPapers.Add(new Paper() { PaperName = "Paper5", IsPending = false });
    }

    public static bool IsCheckingPending
    {
        get
        {
            //List has items and it is not null, so intentionally removed the checks.
            return ListPapers.Count(paper => paper.IsPending == true) > 0 ? true : false;
        }
    }
}

/// <summary>
/// This class will select papers for processing
/// </summary>
public class ChangePaperSetting
{
    public void SelectPaper(string paperName)
    {
        //It can be assumed that Paper object will never be NULL
        PaperChecking.ListPapers.FirstOrDefault(paper => paper.PaperName.Equals(paperName)).IsPending = true;

    }
}

现在，我想使用属性PaperChecking.IsCheckingPending在我的WPF窗口中显示一些控件。我已使用我的控件的可见性绑定了相同的属性。当窗口首次加载行为时，因为Collection已经存在。但是在运行时，我正在更改Paper对象的Pending状态，如下所示：

    ChangePaperSetting changePaperSetting = new ChangePaperSetting();
    changePaperSetting.SelectPaper("Paper1");
    changePaperSetting.SelectPaper("Paper2");
    changePaperSetting.SelectPaper("Paper5");

在我的收藏中，现在我的论文中有IsPending为真。所以现在PaperChecking.IsCheckingPending将返回TRUE，并且根据我的控件现在应该可见。

在普通对象中，我可以实现INotifyPropertyChanged，但在上面的情况下，我没有在属性上设置Setter。有没有办法做这个或任何其他整齐的方法使用相同的类类结构。

//-------------------------------------------------------------------------------//

更新

正如Josh所说，我尝试过这样的事情：

/// <summary>
/// Paper Class
/// </summary>
public class Paper : INotifyPropertyChanged
{
    public string PaperName { get; set; }
    private bool isPending;

    public bool IsPending
    {
        get
        {
            return isPending;
        }
        set
        {
            if (isPending != value)
            {
                isPending = value;
                PropertyChanged(this, new PropertyChangedEventArgs("IsPending"));
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

/// <summary>
/// PaperChecking class, Individual papers will be processed here.
/// </summary>
public class PaperChecking : Control
{

    public static List<Paper> listOfPapers { get; set; }

    public static bool IsCheckingPending
    {
        get
        {
            //List has items and it is not null, so intentionally removed the checks.
            try
            {
                return listOfPapers.Count(paper => paper.IsPending == true) > 0 ? true : false;
            }
            catch (Exception ex) { return false; }
        }
    }


    public static event PropertyChangedEventHandler PropertyChanged;
    public  static void PendingStatusChanged(object sender,PropertyChangedEventArgs e)
    {
        if (e.PropertyName == "IsPending")
        {                
           //If I keep it static, It given Null Reference Error 
           //and If I implement INotifyPropertyChanged interface 
           //in this Class, it gives compilation error because 
           //I am doing so in my Static property.

            PropertyChanged(null,new PropertyChangedEventArgs("IsCheckingPending"));
        }
    }

}

/// <summary>
/// This class will select papers for processing
/// </summary>
public class ChangePaperSetting
{
     public static void AddPapers()
    {

       var listOfPapers = new List<Paper>();
        for (int i = 0; i < 5; i++)
        {
            var paper = new Paper() { PaperName = "Paper"+i.ToString(), 
                                      IsPending = false };
            paper.PropertyChanged+=PaperChecking.PendingStatusChanged;
            listOfPapers.Add(paper);
        }
        PaperChecking.listOfPapers = listOfPapers;
    }
    public void SelectPaper(string paperName)
    {
        //It can be assumed that Paper object will never be NULL
        PaperChecking.listOfPapers.FirstOrDefault(paper => paper.PaperName.Equals(paperName)).IsPending = true;
    }
}

这是我的XAML代码：

<Window xmlns:my="clr-namespace:LearningWpf"  x:Class="LearningWpf.Window4"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window4" Height="300" Width="300"     
    >
<Window.Resources>
    <my:PaperChecking x:Key="paperChecking"/>
    <BooleanToVisibilityConverter x:Key="bvc" />
</Window.Resources>
<StackPanel>
    <Button Name="btn1" Content="Button1" Height="20" Width="80" Click="btn1_Click"></Button>
    <Button Name="btn2" Content="Button2" Height="20" Width="80" Click="btn2_Click"></Button>
    <Button Name="btn3" Content="Button3" Height="20" Width="80" 
            Visibility="{Binding Source={StaticResource paperChecking},
                         Path=IsCheckingPending,
                         Converter={StaticResource bvc}}"></Button>
</StackPanel>

这是我的CodeBehind.cs

public partial class Window4 : Window
{
    public Window4()
    {
        InitializeComponent();
    }

    private void btn1_Click(object sender, RoutedEventArgs e)
    {
        ChangePaperSetting.AddPapers();

    }

    private void btn2_Click(object sender, RoutedEventArgs e)
    {
        var v = PaperChecking.listOfPapers.FirstOrDefault(paper => 
                 paper.PaperName == "Paper1");
        v.IsPending = true;
    }
}

但是这段代码给出了错误，因为我在不初始化的情况下使用静态变量。如果有任何更正或任何其他方法来实现相同的目标。非常感谢您的帮助。

Answer 1

偏离主题，但为什么PaperChecking中的所有属性和功能都是静态的？

要解决您的问题，请向PaperChecking添加新功能并实施INotifyPropertyChanged。

public void SelectPaper(string paperName)
{
    var paper = ListPapers.FirstOrDefault(paper => paper.PaperName.Equals(paperName));
    if (paper != null)
    {
        paper.IsPending = true;
        PropertyChanged("IsCheckingPending");
    }
}

我假设您知道如何实施INotifyPropertyChanged，并有自己的方式来举起活动。没有什么可以说你必须从一个财产的设置者那里提起这个事件。

每次查询时，让您的财产获取者循环浏览整个文件列表是非常低效的。它可以并且将会经常被调用。几乎任何鼠标或键盘事件。每次在Paper上更改挂起状态时，都应尝试缓存计数值。这将需要更多的工作，但它可能值得做。

编辑：

实际上对象可以从多个接口更新，并且它们不会调用相同的方法，它们引用PAPER对象并直接更新属性，而不是在PaperChecking类中调用方法

在这种情况下，您应该在Paper类上实现INotifyPropertyChanged，然后在PaperChecking内监听这些更新。

public void PaperChanged(object sender, PropertyChangedEventArgs args)
{
    if (args.PropertyName == 'IsPending') PropertyChanged("IsCheckingPending");
}

public void AddPapers()
{
    ListPapers = new List<Paper>();

    ListPapers.Add(new Paper() { PaperName = "Paper1", IsPending = false });
    ListPapers.Add(new Paper() { PaperName = "Paper2", IsPending = false });
    ListPapers.Add(new Paper() { PaperName = "Paper3", IsPending = false });
    ListPapers.Add(new Paper() { PaperName = "Paper4", IsPending = false });
    ListPapers.Add(new Paper() { PaperName = "Paper5", IsPending = false });
    foreach(var paper in ListPapers) 
    {
        paper.PropertyChanged += PaperChanged;
    }
}

您还需要将PaperChecking转换为使用实例方法和属性而不是静态方法的类。如果您还不了解MVVM，我建议reading up on it。基本上，您要做的是创建PaperChecking的实例，并将其设置为View后面代码中的DataSource。然后，在您的XAML中，您可以像这样绑定：

<Button Name="btn3" Content="Button3" Height="20" Width="80" 
  Visibility="{Binding IsCheckingPending, Converter={StaticResource bvc}}" />

使用WPF开始时，静态属性和方法几乎总是错误的。知道什么时候需要使用它们，以及何时尝试让自己更容易。

Answer 2

由于您正在使用CLR属性，因此您有责任通知UI底层绑定属性已更改，这只能通过从代码中引发PropertyChanged事件来实现。首先将集合设为ObservableCollection，因为它实现了INotifyCollectionChanged和INotifyPropertyChanged。将集合更改事件与您的集合挂钩，并在处理程序中简单地为您的属性引发propertyChanged事件，如下所示 -

ObservableCollection<Paper> listOfPapers =  new ObservableCollection<Paper>();
listOfPapers.CollectionChanged += new NotifyCollectionChangedEventHandler(listOfPapers_CollectionChanged);

void listOfPapers_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
       OnPropertyChanged("IsCheckingPending");
}

使用这种方法，您不必担心是否需要从SelectPaper（）以外的方法添加集合中的项目。

其他可能的解决方案可能是使用Dependency Property而不是普通的CLR属性，这样您就不必担心提升显式更改的属性。

http://msdn.microsoft.com/en-us/library/ms752914.aspx

Answer 3

这样的事，也许？

private static bool _isCheckingPending;
public static bool IsCheckingPending 
{ 
    get 
    {             
        bool pending = ListPapers.Count(paper => paper.IsPending == true) > 0;

        if (pending != _isCheckingPending) 
        {
           PropertyChanged("IsCheckingPending");
           _isCheckingPending = pending;
        }

        //List has items and it is not null, so intentionally removed the checks. 
        return _isCheckingPending;
    } 
}

这个想法是它记得上次的结果，如果它与这次的结果不同，举起PropertyChanged事件（当然你也会实现INotifyPropertyChanged）。

使用“Get Only”静态属性作为绑定源

3 个答案: