C#和WPF中的命令
我有非常简单的代码,但它不工作 我有一个命令:C#和WPF中的命令,c#,wpf,C#,Wpf,我有非常简单的代码,但它不工作 我有一个命令: public class SetYesCommand : ICommand , INotifyPropertyChanged { public event EventHandler CanExecuteChanged; public event PropertyChangedEventHandler PropertyChanged; ViewModelBase view = new View
public class SetYesCommand : ICommand , INotifyPropertyChanged
{
public event EventHandler CanExecuteChanged;
public event PropertyChangedEventHandler PropertyChanged;
ViewModelBase view = new ViewModelBase();
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
view.Sname = "Yes";
MessageBox.Show("Command works");
onpropertychanged("Sname");
}
private void onpropertychanged(string propertyname)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
}
}
}
}
这是我的基本视图模型类:
public class ViewModelBase : INotifyPropertyChanged
{
private string _s;
public string Sname {
get { return _s; }
set { _s = value;
onPropertyChanged("Sname");
}
}
private void onPropertyChanged(string propertyname)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
}
这是我的XAML代码:
<Window x:Class="Test.MainWindow"
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:Test"
mc:Ignorable="d"
xmlns:viewmodel="clr-namespace:Test.ViewModel"
xmlns:commands="clr-namespace:Test.ViewModel.Commands"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<viewmodel:ViewModelBase x:Key="base" ></viewmodel:ViewModelBase>
<viewmodel:Converters x:Key="convert" ></viewmodel:Converters>
<commands:SetYesCommand x:Key="setyes"/>
</Window.Resources>
<StackPanel>
<Button Width="100" Height="30" Command="{StaticResource setyes}"/>
<TextBox DataContext="{StaticResource base}" Text="{Binding Sname , Mode=TwoWay}"/>
<CheckBox DataContext="{StaticResource base}" IsChecked="{Binding Sname , Mode=TwoWay , Converter={StaticResource convert}}" />
<TextBox />
</StackPanel>
</Window>
正如您所看到的,我将UI中的两个元素绑定到视图模型基类中的字符串属性,并为UI中的按钮定义一个命令。该命令之所以有效,是因为正如您所看到的,我使用messagebox对其进行了检查,但UI中另外两个元素(textbox和checkbox)的值没有改变。您似乎对命令和viewmodel之间的关系感到困惑 命令对象应该是viewmodel的属性,而不是反过来 从基本的通用ICommand实现开始
public class BasicCommand: ICommand
{
private readonly Action _execute;
public BasicCommand(Action execute)
{
_execute = execute;
}
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
_execute?.Invoke();
}
public event EventHandler CanExecuteChanged;
}
而不是在viewmodel中,将命令定义为类似以下内容的属性
public class MyViewModel: ViewModelBase
{
public MyViewModel()
{
DoSomethingCommand = new BasicCommamd(()=>OnDoSomething());
}
public ICommand DoSomethingCommand {get;}
private void OnDoSomething()
{
// put whatever you want the command to do here
}
}
现在,您可以将窗口的DataContext设置为MyViewModel的实例,并将按钮的command属性绑定到DoSomethingCommand。您正在SetYesCommand内创建ViewModelBase的新实例,因此view.Sname=“Yes”不会更改绑定到元素的视图模型的Sname属性 这是有效的:
<Window x:Class="Test.MainWindow"
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:Test"
mc:Ignorable="d"
xmlns:viewmodel="clr-namespace:Test.ViewModel"
xmlns:commands="clr-namespace:Test.ViewModel.Commands"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<viewmodel:ViewModelBase x:Key="base" ></viewmodel:ViewModelBase>
<viewmodel:Converters x:Key="convert" ></viewmodel:Converters>
</Window.Resources>
<StackPanel>
<Button Width="100" Height="30" Command="{Binding Source={StaticResource base},Path=YesCommand}"/>
<TextBox DataContext="{StaticResource base}" Text="{Binding Source={StaticResource base},Path=Sname , Mode=TwoWay}"/>
<CheckBox DataContext="{StaticResource base}" IsChecked="{Binding Sname , Mode=TwoWay , Converter={StaticResource convert}}" />
<TextBox />
</StackPanel>
</Window>
public class ViewModelBase : INotifyPropertyChanged
{
private string _s;
private Commands.SetYesCommand _yesCommand;
public ViewModelBase()
{
_yesCommand = new SetYesCommand(this);
}
public string Sname
{
get { return _s; }
set
{
_s = value;
onPropertyChanged("Sname");
}
}
public SetYesCommand YesCommand => _yesCommand;
private void onPropertyChanged(string propertyname)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
}
}
public event PropertyChangedEventHandler PropertyChanged;
}
public class SetYesCommand : ICommand, INotifyPropertyChanged
{
public event EventHandler CanExecuteChanged;
public event PropertyChangedEventHandler PropertyChanged;
private ViewModelBase view;
public SetYesCommand(ViewModelBase view)
{
this.view = view;
}
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
view.Sname = "Yes";
MessageBox.Show("Command works");
onpropertychanged("Sname");
}
private void onpropertychanged(string propertyname)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
}
}
}
公共类ViewModelBase:INotifyPropertyChanged
{
私有字符串;
private Commands.SetYesCommand _yesCommand;
公共ViewModelBase()
{
_yesCommand=新设置yesCommand(此);
}
公共字符串Sname
{
获取{return}
设置
{
_s=值;
不动产变更(“Sname”);
}
}
公共设置YesCommand和YesCommand=>\u YesCommand;
私有void onPropertyChanged(字符串propertyname)
{
if(PropertyChanged!=null)
{
PropertyChanged(这是新的PropertyChangedEventArgs(propertyname));
}
}
公共事件属性更改事件处理程序属性更改;
}
公共类SetYesCommand:ICommand,INotifyPropertyChanged
{
公共事件处理程序CanExecuteChanged;
公共事件属性更改事件处理程序属性更改;
私有视图模型库视图;
公共设置是命令(ViewModelBase视图)
{
this.view=视图;
}
公共布尔CanExecute(对象参数)
{
返回true;
}
public void Execute(对象参数)
{
view.Sname=“是”;
MessageBox.Show(“命令工作”);
不动产变更(“Sname”);
}
私有void onpropertychanged(字符串propertyname)
{
if(PropertyChanged!=null)
{
PropertyChanged(这是新的PropertyChangedEventArgs(propertyname));
}
}
}
您正在命令中创建ViewModelBase
的新实例。应该是视图模型创建命令,而不是相反
ICommand
接口的典型实现通常接受要执行的操作
,以及决定是否执行命令的谓词
:
public class SetYesCommand : ICommand
{
public event EventHandler CanExecuteChanged;
private readonly Action<object> _execute;
private readonly Predicate<object> _canExecute;
public SetYesCommand(Action<object> execute, Predicate<object> canExecute)
{
_execute = execute;
_canExecute = canExecute;
}
public bool CanExecute(object parameter)
{
if (_canExecute == null)
return true;
return _canExecute(parameter);
}
public void Execute(object parameter)
{
if (_execute != null)
_execute(parameter);
}
}
在视图中,您绑定到视图模型的命令属性,该属性返回ICommand
实现的实例:
<Button Width="100" Height="30" DataContext="{StaticResource base}" Command="{Binding TheCommand}"/>
您正在命令中创建ViewModelBase的新实例。应该创建命令的是视图模型,而不是相反的方式。@mm8我也用静态属性尝试过它,但它不能以那种方式工作。是的,我是MVVM的新手,有点困惑,谢谢。看看我的博客,看看我对WPF/MVVM的看法——这太好了,谢谢你,但我仍然无法理解为什么即使我的属性是静态的,它也不能工作。
<Button Width="100" Height="30" DataContext="{StaticResource base}" Command="{Binding TheCommand}"/>