gpt4 book ai didi

c# - RelayCommand 不会在按钮单击时执行

转载 作者:行者123 更新时间:2023-12-03 10:55:16 26 4
gpt4 key购买 nike

我已经在这个问题上停留了几个小时。我正在尝试在 WPF 中实现 MVVM 样式的 Word 加载项。我没有使用 MVVM 工具包。我有一个停靠在 WinForm 中的 WPF 用户控件。虽然我能够在 win 表单中看到 WPF 用户控件并与之交互,但我的通用 RelayCommand<T>当我单击按钮时,绑定(bind)到 WPF 按钮将不会执行。 RelayCommand住在 ViewModel.cs 和 DataContext因为 View 是通过代码隐藏设置的。我确定我在做一些愚蠢的事情,但无法弄清楚它是什么,因此不确定为什么 RelayCommand属性(property)的get{}不会被执行。请看下面的代码。在此先感谢您的帮助!

RelayCommand.cs (代码片段不包括命名空间并包含语句)

/// <summary>
/// RelayCommand
/// </summary>
/// <typeparam name="T">Generic Parameter</typeparam>
public class RelayCommand<T> : ICommand where T : class
{
#region Constructors

/// <summary>
/// RelayCommand constructor
/// </summary>
/// <param name="exec">Delegate that encapsulates a method that takes in a single parameter and returns void</param>
/// <param name="canExec">Delegate that encapsulates a method that defines a set of criteria and returns a true if criteria is met; else false</param>
public RelayCommand(Action<T> execute, Predicate<T> canExecute = null)
{
if (execute == null)
throw new ArgumentNullException("execute is null");

_canExecute = canExecute;
_execute = execute;
}

#endregion
#region Members

/// <summary>
/// Execute method
/// </summary>
/// <param name="param">Parameter</param>
public void Execute(object param)
{
T obj = param as T;

if(obj != null)
{
_execute(obj);
}
}

/// <summary>
/// CanExec is a method that shows whether or not execution can happen
/// </summary>
/// <param name="param">Parameter</param>
/// <returns>true if can execute; else false</returns>
public bool CanExecute(object param)
{
if (_canExecute == null)
return true;

T obj = param as T;
return obj == null || _canExecute(obj);
}

/// <summary>
/// CanExec event changed
/// </summary>
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}

#endregion

#region Fields

private readonly Predicate<T> _canExecute;
private readonly Action<T> _execute;

#endregion
}

提交用户控制.xaml (只有相关的片段。不包括一些代码)
<Button Grid.Column="2" x:Name="SubmitButton" Command="{Binding Path=SubmitCommentCommand}"
Content="Submit" HorizontalAlignment="Right" Margin="5"/>

SubmissionUserControl.xaml.cs (包含我引用 ViewModel 的片段)
ViewModel viewModel;
public SubmissionUserControl()
{
InitializeComponent();
viewModel = new ViewModel();
DataContext = viewModel;
}

ViewModel.cs (不包括一些代码。只显示相关的RelayCommand)
/// <summary>
/// SubmitCommentCommand responsible for interacting with UI to submit a comment.
/// </summary>
/// <returns>Returns a RelayCommand that executes a method to Save comments from the comment box</returns>
public ICommand SubmitCommentCommand
{
get
{
return _submitCommentCommand ?? (_submitCommentCommand = new RelayCommand<object>(param => this.SaveComment()));
}
}

最佳答案

为了让您更详细地了解 MVVM 和 RelayCommands:

您不必在 Xaml 中声明您的 ViewModel,这主要是在应用程序根级别以编程方式完成的,可能使用一些 DI。

当坚持这个MSDN Article你的 RelayCommand 应该是这样的:

public class RelayCommand : ICommand
{
#region Fields

readonly Action<object> _execute;
readonly Predicate<object> _canExecute;

#endregion // Fields

#region Constructors

public RelayCommand(Action<object> execute)
: this(execute, null)
{
}

public RelayCommand(Action<object> execute, Predicate<object> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");

_execute = execute;
_canExecute = canExecute;
}
#endregion // Constructors

#region ICommand Members

[DebuggerStepThrough]
public bool CanExecute(object parameter)
{
return _canExecute == null ? true : _canExecute(parameter);
}

public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}

public void Execute(object parameter)
{
_execute(parameter);
}

#endregion // ICommand Members
}

此外,您可以定义一个通用的 RelayCommand 来处理命令参数,如下所示:
public class GenericRelayCommand<T> : ICommand
{
private readonly Action<T> _execute;
public Predicate<T> CanExecuteFunc { get; private set; }

public GenericRelayCommand(Action<T> execute) : this(execute, p => true)
{}

public GenericRelayCommand(Action<T> execute, Predicate<T> canExecuteFunc)
{
_execute = execute;
CanExecuteFunc = canExecuteFunc;
}

public bool CanExecute(object parameter)
{
var canExecute = CanExecuteFunc((T)parameter);
return canExecute;
}

public void Execute(object parameter)
{
_execute((T)parameter);
}

public event EventHandler CanExecuteChanged
{
add
{
CommandManager.RequerySuggested += value;
}
remove
{
CommandManager.RequerySuggested -= value;
}
}
}

在您的 ViewModel 中,应像这样定义 RelayCommands(我还实现了 INotifyPropertyChanged 以用于进一步的 WPF Xaml 属性处理示例):
public class ViewModel : INotifyPropertyChanged
{
private string _comment;
public string Comment
{
get { return _comment; }
set { _comment = value; OnPropertyChanged("Comment"); }
}

public GenericRelayCommand<string> SubmitComment1Command { get; set; }
public RelayCommand SubmitComment2Command { get; set; }

public ViewModel()
{
Comment = "Hello World!";
SubmitComment1Command = new GenericRelayCommand<string>(OnSubmitComment1);
SubmitComment2Command = new RelayCommand(OnSubmitComment2);
}

private void OnSubmitComment1(string obj)
{
//Save Comment Mock with CommandParameter
MessageBox.Show(obj);
}

private void OnSubmitComment2(object obj)
{
//Save Comment Mock with Property
MessageBox.Show(Comment);
}

public event PropertyChangedEventHandler PropertyChanged;

protected virtual void OnPropertyChanged(string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}

我将您的按钮示例放入一个新的 WPF 应用程序中,如下所示:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow"
Width="525"
Height="350">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition />
<ColumnDefinition />
</Grid.ColumnDefinitions>

<StackPanel Grid.Column="0"
Orientation="Horizontal">
<TextBox Name="textBox"
Width="200"
Text="{Binding Comment,
Mode=TwoWay,
UpdateSourceTrigger=PropertyChanged}" />
<Button x:Name="SubmitButton1"
Grid.Column="0"
Margin="5"
HorizontalAlignment="Right"
Command="{Binding Path=SubmitComment1Command}"
CommandParameter="{Binding ElementName=textBox,
Path=Text}"
Content="Submit1" />
</StackPanel>


<Button x:Name="SubmitButton2"
Grid.Column="1"
Margin="5"
HorizontalAlignment="Right"
Command="{Binding Path=SubmitComment2Command}"
Content="Submit2" />
</Grid>
</Window>

为了简单起见,像这样设置 DataContext (如前所述,这通常是通过某种根级别的 DI 来完成的):
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
DataContext = new ViewModel();
}
}

然后一切都应该正常工作。

关于c# - RelayCommand 不会在按钮单击时执行,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21821762/

26 4 0
Copyright 2021 - 2024 cfsdn All Rights Reserved 蜀ICP备2022000587号
广告合作:1813099741@qq.com 6ren.com