2. Prism系列之命令

Prism系列之命令

---

---

一、创建命令

新建一个WPF工程，创建名为 CommandNewSample的WPF项目。

分别创建Views文件夹和ViewModels文件夹，将MainWindow放在Views文件夹下，再在ViewModels文件夹下面创建MainWindowViewModel类。

xaml代码如下：

<Window x:Class="CommandNewSample.Views.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:CommandNewSample"
        xmlns:prism="http://prismlibrary.com/"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="450"
        prism:ViewModelLocator.AutoWireViewModel="True">
    <StackPanel>
        <TextBox Margin="10" Text="{Binding CurrentTime}" FontSize="32"/>
        <Button  x:Name="btnMe"  FontSize="30"  Content="Click Me" Margin="10" Height="60" Command="{Binding GetCurrentTimeCommand}"/>
        <Viewbox Height="80" >
            <CheckBox IsChecked="{Binding IsCanExecute}"  Content="CanExcute" Margin="10"  HorizontalAlignment="Center" VerticalAlignment="Center" />
        Viewbox>
    StackPanel>
Window>

MainWindowViewModel类代码如下：

using Prism.Commands;
using Prism.Mvvm;

namespace CommandNewSample.ViewModels
{
    public class MainWindowViewModel : BindableBase
    {
        private bool _isCanExecute;
        public bool IsCanExecute
        {
            get { return _isCanExecute; }
            set
            {
                SetProperty(ref _isCanExecute, value);
                GetCurrentTimeCommand.RaiseCanExecuteChanged();
            }
        }

        private string _currentTime;
        public string CurrentTime
        {
            get { return _currentTime; }
            set { SetProperty(ref _currentTime, value); }
        }

        private DelegateCommand _getCurrentTimeCommand;
        public DelegateCommand GetCurrentTimeCommand =>
            _getCurrentTimeCommand ?? (_getCurrentTimeCommand = new DelegateCommand(ExecuteGetCurrentTimeCommand, CanExecuteGetCurrentTimeCommand));

        void ExecuteGetCurrentTimeCommand()
        {
            this.CurrentTime = DateTime.Now.ToString();
        }

        bool CanExecuteGetCurrentTimeCommand()
        {
            return IsCanExecute;
        }
    }
}

启动程序：

点击按钮:

在代码中，我们通过using Prism.Mvvm引入继承BindableBase，因为我们要用到属性改变通知方法SetProperty，这在我们上一篇就知道了，再来我们using Prism.Commands，我们所定义的DelegateCommand类型就在该命名空间下。

我们知道，ICommand接口是有三个函数成员的，事件CanExecuteChanged，一个返回值bool的，且带一个参数为object的CanExecute方法，一个无返回值且带一个参数为object的Execute方法，很明显我们实现的GetCurrentTimeCommand命令就是一个不带参数的命令。

还有一个值得注意的是，我们通过Checkbox的IsChecked绑定了一个bool属性IsCanExcute，且在CanExecute方法中return IsCanExcute，我们都知道CanExecute控制着Execute方法的是否能够执行，也控制着Button的IsEnable状态,而在IsCanExcute的set方法我们增加了一句：

GetCurrentTimeCommand.RaiseCanExecuteChanged();

其实上述prism还提供了一个更简洁优雅的写法：

 private bool _isCanExcute;
 public bool IsCanExcute
 {
    get { return _isCanExcute; }
    set { SetProperty(ref _isCanExcute, value);}
 }

 private DelegateCommand _getCurrentTimeCommand;
 public DelegateCommand GetCurrentTimeCommand =>
    _getCurrentTimeCommand ?? (_getCurrentTimeCommand = new  DelegateCommand(ExecuteGetCurrentTimeCommand).ObservesCanExecute(()=> IsCanExcute));

 void ExecuteGetCurrentTimeCommand()
 {
    this.CurrentTime = DateTime.Now.ToString();
 }

其中用了ObservesCanExecute方法，其实在该方法内部中也是会去调用RaiseCanExecuteChanged方法。

二、创建有参命令

我们可以看看DelegateCommand的继承链和暴露出来的公共方法，详细的实现可以去看下源码

我们之前创建DelegateCommand不是泛型版本，当创建一个泛型版本的DelegateCommand,那么T就是我们要传入的命令参数的类型，那么，我们现在可以把触发命令的Button本身作为命令参数传入。

xaml代码如下：

<Button  x:Name="btnMeT"  FontSize="30"  Content="Click Me(T)" Margin="10" Height="60" Command="{Binding GetCurrentTimeCommand}"  CommandParameter="{Binding RelativeSource={RelativeSource Mode=Self}}"/>

GetCurrentTimeCommand命令代码改为如下：

       private bool _isCanExecute;
       public bool IsCanExecute
       {
           get { return _isCanExecute; }
           set { SetProperty(ref _isCanExecute, value); }
       }

       private string _currentTime;
       public string CurrentTime
       {
           get { return _currentTime; }
           set { SetProperty(ref _currentTime, value); }
       }

       private DelegateCommand<object> _getCurrentTimeCommand;
       public DelegateCommand<object> GetCurrentTimeCommand =>
          _getCurrentTimeCommand ?? (_getCurrentTimeCommand = new DelegateCommand<object>(ExecuteGetCurrentTimeCommand).ObservesCanExecute(() => IsCanExecute));

       void ExecuteGetCurrentTimeCommand(object parameter)
       {
           this.CurrentTime = ((Button)parameter)?.Name + DateTime.Now.ToString();
       }

点击按钮:

三、事件转命令

1. 无参命令

在我们大多数拥有Command依赖属性的控件，大多数是由于继承了ICommandSource接口，ICommandSource接口拥有着三个函数成员ICommand接口类型属性Command，object 类型属性CommandParameter,IInputElement类型属性CommandTarget，而基本继承着ICommandSource接口这两个基础类的就是ButtonBase和MenuItem，因此像Button，Checkbox，RadioButton等继承自ButtonBase拥有着Command依赖属性，而MenuItem也同理。但是我们常用的Textbox那些就没有。

现在我们有这种需求，我们要在这个界面基础上新增第二个Textbox，当Textbox的文本变化时，需要将按钮的Name和第二个Textbox的文本字符串合并更新到第一个Textbox上，我们第一直觉肯定会想到用Textbox的TextChanged事件，那么如何将TextChanged转为命令？

首先在xaml界面引入：

xmlns:i="http://schemas.microsoft.com/xaml/behaviors"

然后我们新增第二个Textbox的代码：

<TextBox Margin="10" FontSize="32" Text="{Binding Foo,UpdateSourceTrigger=PropertyChanged}">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="TextChanged">
            <i:InvokeCommandAction Command="{Binding TextChangedCommand}" CommandParameter="{Binding ElementName=mybtn}"/>
        i:EventTrigger>
    i:Interaction.Triggers>
TextBox>

MainWindowViewModel新增代码：

private string _foo;
public string Foo
{
    get { return _foo; }
    set { SetProperty(ref _foo, value); }
}

private DelegateCommand<object> _textChangedCommand;
public DelegateCommand<object> TextChangedCommand =>
  _textChangedCommand ?? (_textChangedCommand = new DelegateCommand<object>(ExecuteTextChangedCommand));

void ExecuteTextChangedCommand(object parameter)
{
    this.CurrentTime = Foo + ((Button)parameter)?.Name;
}

上面我们在xaml代码就是添加了对TextBox的TextChanged事件的Blend EventTrigger的侦听，每当触发该事件，InvokeCommandAction就会去调用TextChangedCommand命令。

2. 有参命令

TextChanged事件是有个RoutedEventArgs参数TextChangedEventArgs，假如我们要拿到该TextChangedEventArgs或者是RoutedEventArgs参数里面的属性，用prism自带的InvokeCommandAction的TriggerParameterPath属性。

我们现在有个要求，我们要在第一个TextBox，显示我们第二个TextBox输入的字符串加上触发该事件的控件的名字，那么我们可以用到其父类RoutedEventArgs的Soucre属性，而激发该事件的控件就是第二个TextBox。

xaml代码修改如下：

<TextBox x:Name="myTextBox" Margin="10" FontSize="32" Text="{Binding Foo,UpdateSourceTrigger=PropertyChanged}" TextChanged="TextBox_TextChanged">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="TextChanged">
            <prism:InvokeCommandAction Command="{Binding TextChangedCommand}"  TriggerParameterPath="Source"/>
        i:EventTrigger>
    i:Interaction.Triggers>
TextBox>

MainWindowViewModel修改如下：

void ExecuteTextChangedCommand(object parameter)
{
    this.CurrentTime = Foo + ((TextBox)parameter)?.Name;
}

四、基于Task的命令

在界面新增一个新的按钮，用来绑定新的基于Task的命令,我们将要做的就是点击该按钮后，第一个Textbox的在5秒后显示"Hello Prism Task!",且期间UI界面不阻塞

xaml界面新增按钮代码如下：

<Button  x:Name="btnTask"  FontSize="30"  Content="Click Me Task" Margin="10" Height="60" Command="{Binding AsyncCommand}" />

MainWindowViewModel新增代码：

private DelegateCommand _asyncCommand;
public DelegateCommand AsyncCommand =>
    _asyncCommand ?? (_asyncCommand = new DelegateCommand(
        async() => await ExecuteAsyncCommand()));

Task ExecuteAsyncCommand()
{
    return Task.Run(() =>
    {
        Thread.Sleep(5000);
        this.CurrentTime = "Hello Prism Task";
    });
}

点击按钮:

五、创建复合命令

prism提供CompositeCommand类支持复合命令。

什么是复合命令？

我们可能有这种场景，一个主界面的不同子窗体都有其各自的业务，假如我们可以将上面的例子稍微改下，我们分为三个不同子窗体，三个分别来显示当前年份，月日，时分秒，我们希望在主窗体提供一个按钮，点击后能够使其同时显示，这时候就有一种关系存在了，主窗体按钮依赖于三个子窗体的按钮，而子窗体的按钮不依赖于主窗体的按钮

下面是创建和使用一个prism标准复合命令的流程：

1. 创建一个全局的复合命令
2. 通过IOC容器注册其为单例
3. 给复合命令注册子命令
4. 绑定复合命令

1. 创建一个全局的复合命令

创建一个类库项目，新增ApplicationCommands类作为全局命令类，代码如下：

using Prism.Commands;

namespace CompositeCommandCore
{
    public interface IApplicationCommands
    {
        CompositeCommand GetCurrentAllTimeCommand { get; }
    }

    public class ApplicationCommands : IApplicationCommands
    {
        private CompositeCommand _getCurrentAllTimeCommand = new CompositeCommand();
        public CompositeCommand GetCurrentAllTimeCommand
        {
            get { return _getCurrentAllTimeCommand; }
        }
    }
}

其中我们创建了IApplicationCommands接口，让ApplicationCommands实现了该接口，目的是为了下一步通过IOC容器注册其为全局的单例接口

2. 通过IOC容器注册其为单例

创建一个新的项目作为主窗体，用来显示子窗体和使用复合命令，关键部分代码如下：

App.xaml.cs代码：

using CompositeCommandCore;
using CompositeCommandsSample.Views;
using Prism.Ioc;
using Prism.Modularity;
using Prism.Unity;
using System.Windows;

namespace CompositeCommandsSample
{
    /// 

    /// Interaction logic for App.xaml
    /// 
    public partial class App : PrismApplication
    {
        protected override Window CreateShell()
        {
            return Container.Resolve<MainWindow>();
        }

        //通过IOC容器注册IApplicationCommands为单例
        protected override void RegisterTypes(IContainerRegistry containerRegistry)
        {
            containerRegistry.RegisterSingleton<IApplicationCommands, ApplicationCommands>();
        }

        //注册子窗体模块
        protected override void ConfigureModuleCatalog(IModuleCatalog moduleCatalog)
        {
            moduleCatalog.AddModule<CommandNewSample.CommandSampleMoudle>();
        }
    }
}

App.xaml

<prism:PrismApplication  xmlns:prism="http://prismlibrary.com/" x:Class="CompositeCommandsSample.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:CompositeCommandsSample">
    <Application.Resources>
         
    </Application.Resources>
</prism:PrismApplication>

3. 给复合命令注册子命令

在之前的CommandSample解决方案下面的Views文件夹下新增两个UserControl，分别用来显示月日和时分秒，在其ViewModels文件夹下面新增两个UserControl的ViewModel，并且将之前的MainWindow也改为UserControl，大致结构如下图：

GetHourTabViewModel.cs:

using CompositeCommandCore;
using Prism.Commands;
using Prism.Mvvm;

namespace CommandNewSample.ViewModels
{
    public class GetHourTabViewModel : BindableBase
    {
        IApplicationCommands _applicationCommands;

        private string _currentHour;
        public string CurrentHour
        {
            get { return _currentHour; }
            set { SetProperty(ref _currentHour, value); }
        }

        public GetHourTabViewModel(IApplicationCommands applicationCommands)
        {
            _applicationCommands = applicationCommands;
            //给复合命令GetCurrentAllTimeCommand注册子命令GetHourCommand
            _applicationCommands.GetCurrentAllTimeCommand.RegisterCommand(GetHourCommand);
        }


        private string _title;
        public string Title
        {
            get { return _title; }
            set { SetProperty(ref _title, value); }
        }

        private bool _isCanExecute;
        public bool IsCanExecute
        {
            get { return _isCanExecute; }
            set { SetProperty(ref _isCanExecute, value); }
        }

        private DelegateCommand _getHourCommand;
        public DelegateCommand GetHourCommand =>
           _getHourCommand ?? (_getHourCommand = new DelegateCommand(ExecuteGetHourCommand).ObservesCanExecute(() => IsCanExecute));

        void ExecuteGetHourCommand()
        {
            this.CurrentHour = DateTime.Now.ToString("HH:mm:ss");
        }

    }
}

GetMonthDayTabViewModel.cs

using CompositeCommandCore;
using Prism.Commands;
using Prism.Mvvm;

namespace CommandNewSample.ViewModels
{
    public class GetMonthDayTabViewModel : BindableBase
    {
        IApplicationCommands _applicationCommands;

        private string _currentMonthDay;
        public string CurrentMonthDay
        {
            get { return _currentMonthDay; }
            set { SetProperty(ref _currentMonthDay, value); }
        }

        private bool _isCanExecute;
        public bool IsCanExecute
        {
            get { return _isCanExecute; }
            set { SetProperty(ref _isCanExecute, value); }
        }


        private string _title;
        public string Title
        {
            get { return _title; }
            set { SetProperty(ref _title, value); }
        }

        public GetMonthDayTabViewModel(IApplicationCommands applicationCommands)
        {
            _applicationCommands = applicationCommands;
            //给复合命令GetCurrentAllTimeCommand注册子命令GetMonthCommand
            _applicationCommands.GetCurrentAllTimeCommand.RegisterCommand(GetMonthCommand);
        }

        private DelegateCommand _getMonthCommand;
        public DelegateCommand GetMonthCommand =>
             _getMonthCommand ?? (_getMonthCommand = new DelegateCommand(ExecuteCommandName).ObservesCanExecute(() => IsCanExecute));

        void ExecuteCommandName()
        {
            this.CurrentMonthDay = DateTime.Now.ToString("MM:dd");
        }

    }
}

MainWindowViewModel.cs:

using CompositeCommandCore;
using Prism.Commands;
using Prism.Mvvm;
using System.Windows.Controls;

namespace CommandNewSample.ViewModels
{
    public class MainWindowViewModel : BindableBase
    {
        private bool _isCanExecute;
        public bool IsCanExecute
        {
            get { return _isCanExecute; }
            set { SetProperty(ref _isCanExecute, value); }
        }

        private string _currentTime;
        public string CurrentTime
        {
            get { return _currentTime; }
            set { SetProperty(ref _currentTime, value); }
        }


        private DelegateCommand<object> _getCurrentTimeCommand;
        public DelegateCommand<object> GetCurrentTimeCommand =>
           _getCurrentTimeCommand ?? (_getCurrentTimeCommand = new DelegateCommand<object>(ExecuteGetCurrentTimeCommand).ObservesCanExecute(() => IsCanExecute));

        void ExecuteGetCurrentTimeCommand(object parameter)
        {
            this.CurrentTime = ((Button)parameter)?.Name + DateTime.Now.ToString();
        }


        private string _foo;
        public string Foo
        {
            get { return _foo; }
            set { SetProperty(ref _foo, value); }
        }

        private DelegateCommand<object> _textChangedCommand;
        public DelegateCommand<object> TextChangedCommand =>
          _textChangedCommand ?? (_textChangedCommand = new DelegateCommand<object>(ExecuteTextChangedCommand));

        void ExecuteTextChangedCommand(object parameter)
        {
            this.CurrentTime = Foo + ((TextBox)parameter)?.Name;
        }


        private DelegateCommand _asyncCommand;
        public DelegateCommand AsyncCommand =>
            _asyncCommand ?? (_asyncCommand = new DelegateCommand(
                async() => await ExecuteAsyncCommand()));

        Task ExecuteAsyncCommand()
        {
            return Task.Run(() =>
            {
                Thread.Sleep(5000);
                this.CurrentTime = "Hello Prism Task";
            });
        }

        private string _title;
        public string Title
        {
            get { return _title; }
            set { SetProperty(ref _title, value); }
        }

        IApplicationCommands _applicationCommands;

        public MainWindowViewModel(IApplicationCommands applicationCommands)
        {
            _applicationCommands = applicationCommands;
            //给复合命令GetCurrentAllTimeCommand注册子命令GetYearCommand
            _applicationCommands.GetCurrentAllTimeCommand.RegisterCommand(GetYearCommand);
        }

        private DelegateCommand _getYearCommand;
        public DelegateCommand GetYearCommand =>
           _getYearCommand ?? (_getYearCommand = new DelegateCommand(ExecuteGetYearCommand).ObservesCanExecute(() => IsCanExecute));

        void ExecuteGetYearCommand()
        {
            this.CurrentTime = DateTime.Now.ToString("yyyy");
        }


    }
}

CommandNewSampleMoudle.cs

using CommandNewSample.ViewModels;
using CommandNewSample.Views;
using Prism.Ioc;
using Prism.Modularity;
using Prism.Regions;

namespace CommandNewSample
{
    public class CommandNewSampleMoudle : IModule
    {
        public void OnInitialized(IContainerProvider containerProvider)
        {
            var regionManager = containerProvider.Resolve<IRegionManager>();
            IRegion region = regionManager.Regions["ContentRegion"];

            var mainWindow = containerProvider.Resolve<MainWindow>();
            (mainWindow.DataContext as MainWindowViewModel).Title = "GetYearTab";
            region.Add(mainWindow);

            var getMonthTab = containerProvider.Resolve<GetMonthDayTab>();
            (getMonthTab.DataContext as GetMonthDayTabViewModel).Title = "GetMonthDayTab";
            region.Add(getMonthTab);

            var getHourTab = containerProvider.Resolve<GetHourTab>();
            (getHourTab.DataContext as GetHourTabViewModel).Title = "GetHourTab";
            region.Add(getHourTab);

        }

        public void RegisterTypes(IContainerRegistry containerRegistry)
        {

        }
    }
}

4. 绑定复合命令

MainWindow.xaml

<Window x:Class="CompositeCommandsSample.Views.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:prism="http://prismlibrary.com/"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        Title="MainWindow" Height="650" Width="800">
    <Window.Resources>
        <Style TargetType="TabItem">
            "Header" Value="{Binding DataContext.Title}"/>
        Style>
    Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="*"/>
        Grid.RowDefinitions>
        <Button Content="GetCurrentTime" FontSize="30" Margin="10" Command="{Binding ApplicationCommands.GetCurrentAllTimeCommand}"/>
        <TabControl Grid.Row="1" prism:RegionManager.RegionName="ContentRegion"/>
    Grid>
Window>

MainWindowViewModel.cs：

using CompositeCommandCore;
using Prism.Mvvm;

namespace CompositeCommandsSample.ViewModels
{
    public class MainWindowViewModel : BindableBase
    {
        private IApplicationCommands _applicationCommands;
        public IApplicationCommands ApplicationCommands
        {
            get { return _applicationCommands; }
            set { SetProperty(ref _applicationCommands, value); }
        }

        public MainWindowViewModel(IApplicationCommands applicationCommands)
        {
            this.ApplicationCommands = applicationCommands;
        }
    }
}

点击按钮:

最后，其中复合命令也验证我们一开始说的关系，复合命令依赖于子命令，但子命令不依赖于复合命令，因此，只有当三个子命令的都为可执行的时候才能执行复合命令。

回到顶部

---