我期待在全面实行接力指挥,可以发现这里
我听说后面RelayCommand的想法是有一种“的万能遥控器 ”在您的所有命令使用。
如果是这样的话,我有2个问题与实现:
1)如果某些控制我不想传递参数,会发生什么? 我一定要吗? 我需要改变我的执行/据此可以-执行功能,以支持这些参数?
2)如果我不希望通过在XAML中CommandParameter什么? 如果我想用影响控制的变化属性发生变化,或者在我的代码一些其他的方法。 我能影响CanExecute或CanExecuteChanged没有通过CommandParameter在XAML?
到现在为止我主要实现,其中CanExecute返回真所有的时间部分RelayCommands,我根本绑定的IsEnabled在我的视图模型一个额外的属性控制。 此作品不错,但我不知道 - 我能为我全面推行呢?
(可答案给一个完整的工作示例吗?)
1)的ICommand只有方法,包括的参数。 如果不指定XAML参数,空时使用。
https://msdn.microsoft.com/en-us/library/system.windows.input.icommand(v=vs.110).aspx
2)是的,你可以影响CanExecute没有CommandParameter。 下面看到的,它使用CanExecute视图模型的字符串属性“迈德特”。
MainWindow.xaml
<Window x:Class="WpfApplication8.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:WpfApplication8"
mc:Ignorable="d"
FocusManager.FocusedElement="{Binding ElementName=tb}"
SizeToContent="Height"
Title="MainWindow" Width="525">
<Window.DataContext>
<local:MainWindowViewModel />
</Window.DataContext>
<StackPanel>
<Label Content="MyData (CanExecute returns false if this is whitespace)" />
<TextBox Name="tb" Text="{Binding MyData, UpdateSourceTrigger=PropertyChanged}" Margin="5" />
<Button Content="Without XAML CommandParameter" Margin="5" Command="{Binding Command1}" />
<Button Content="With XAML CommandParameter" Margin="5" Command="{Binding Command1}" CommandParameter="{Binding MyData}" />
</StackPanel>
</Window>
MainWindow.xaml.cs
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Input;
namespace WpfApplication8
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
}
public class MainWindowViewModel : INotifyPropertyChanged
{
private ICommand command1;
public ICommand Command1 { get { return command1; } set { command1 = value; PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Command1))); } }
private string myData;
public string MyData { get { return myData; } set { myData = value; PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(MyData))); } }
public event PropertyChangedEventHandler PropertyChanged;
public MainWindowViewModel()
{
Command1 = new RelayCommand<object>(Command1Execute, Command1CanExecute);
}
private bool Command1CanExecute(object obj)
{
// Only allow execute if MyData has data
return !string.IsNullOrWhiteSpace(MyData);
}
private void Command1Execute(object obj)
{
MessageBox.Show($"CommandParameter = '{obj}'");
}
}
public class RelayCommand<T> : ICommand
{
#region Fields
readonly Action<T> _execute = null;
readonly Predicate<T> _canExecute = null;
#endregion
#region Constructors
/// <summary>
/// Initializes a new instance of <see cref="DelegateCommand{T}"/>.
/// </summary>
/// <param name="execute">Delegate to execute when Execute is called on the command. This can be null to just hook up a CanExecute delegate.</param>
/// <remarks><seealso cref="CanExecute"/> will always return true.</remarks>
public RelayCommand(Action<T> execute)
: this(execute, null)
{
}
/// <summary>
/// Creates a new command.
/// </summary>
/// <param name="execute">The execution logic.</param>
/// <param name="canExecute">The execution status logic.</param>
public RelayCommand(Action<T> execute, Predicate<T> canExecute)
{
if (execute == null)
throw new ArgumentNullException("execute");
_execute = execute;
_canExecute = canExecute;
}
#endregion
#region ICommand Members
///<summary>
///Defines the method that determines whether the command can execute in its current state.
///</summary>
///<param name="parameter">Data used by the command. If the command does not require data to be passed, this object can be set to null.</param>
///<returns>
///true if this command can be executed; otherwise, false.
///</returns>
public bool CanExecute(object parameter)
{
return _canExecute == null ? true : _canExecute((T)parameter);
}
///<summary>
///Occurs when changes occur that affect whether or not the command should execute.
///</summary>
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
///<summary>
///Defines the method to be called when the command is invoked.
///</summary>
///<param name="parameter">Data used by the command. If the command does not require data to be passed, this object can be set to <see langword="null" />.</param>
public void Execute(object parameter)
{
_execute((T)parameter);
}
#endregion
}
}