使用“仅获取”静态属性作为绑定源
本文关键字：属性 绑定 静态 获取 仅获取 使用 | 更新日期: 2023-09-27 18:25:45
>我有下面提到的类结构。
//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。我已将同一属性与控件的可见性绑定在一起。首次加载窗口时，行为是预期的，因为集合已经存在。但是在运行时，当我更改 Paper 对象的待处理状态时，如下所示：
ChangePaperSetting changePaperSetting = new ChangePaperSetting();
changePaperSetting.SelectPaper("Paper1");
changePaperSetting.SelectPaper("Paper2");
changePaperSetting.SelectPaper("Paper5");
在我的收藏中，现在我有论文将IsEnding视为真实。所以现在 PaperChecking.IsCheckingPending 将返回 TRUE，根据该值，我的控件现在应该可见。
在普通对象中，我本可以实现 INotifyPropertyChanged ，但在上述情况下，我在属性上没有 Setter。有没有办法做到这一点或任何其他使用相同类结构的整洁方法。
//-------------------------------------------------------------------------------//
更新
正如乔希所建议的，我尝试了这样的事情：
/// <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>
这是我的代码隐藏.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，很严格，因为我在没有初始化它的情况下使用了静态变量。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。
由于您使用的是 CLR 属性，因此您有责任通知 UI 基础绑定属性已更改，这只能通过从代码中引发 PropertyChanged 事件来实现。首先，使集合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属性更改事件，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(( 以外的方法在集合中添加项目。
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，这样您就不必担心显式更改属性。
http://msdn.microsoft.com/en-us/library/ms752914.aspx
也许是
这样的东西？
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;
}
}
这个想法是它记住上次的结果，如果它与这次的结果不同，则引发 PropertyChanged 事件(当然，您将实现 INotifyPropertyChanged(。
题外话，但为什么 PaperCheck 中的所有属性和函数都是静态的？
但是，要解决您的问题，请添加一个新功能来PaperChecking并实现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现INotifyPropertyChanged，并且有自己的方法来引发事件。没有什么说你必须从属性的设置者那里引发事件。
每次查询时，让您的属性获取者循环浏览整个论文列表是非常非常低效的。它可以而且将经常被调用。几乎与任何鼠标或键盘事件有关。每次更改纸张上的待处理状态时，都应尝试缓存计数值。这将需要更多的工作，但可能值得做。
编辑：
实际上对象可以从多个接口更新，它们不会调用相同的方法，它们引用 PAPER 对象并将直接更新属性，而不是在 PaperCheck 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 中侦听这些更新。
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;
}
}
还需要将PaperChecking转换为使用实例方法和属性而不是静态方法和属性的类。如果你还不知道MVVM，我建议你阅读它。从本质上讲，您要做的是创建一个PaperChecking实例，并将其设置为视图代码中的DataSource。然后，在 XAML 中，只需像这样绑定：
<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，什么时候你想让自己更轻松。