WPF自定义控件与样式(14)-轻量MVVM模式实践

来源:互联网 时间:1970-01-01


一.前言

申明:WPF自定义控件与样式是一个系列文章,前后是有些关联的,但大多是按照由简到繁的顺序逐步发布的,若有不明白的地方可以参考本系列前面的文章,文末附有部分文章链接。

MVVM是WPF中一个非常实用的编程模式,充分利用了WPF的绑定机制,体现了WPF数据驱动的优势。

 图片来源:(WPF的MVVM)

关于MVVM网上很多介绍或者示例,本文不多做介绍了,本文的主要目的是提供一个轻量级的View Model实现,本文的主要内容:

  • 依赖通知InotifyPropertyChanged实现;
  • 命令Icommand的实现;
  • 消息的实现;
  • 一个简单MVVM示例;

对于是否要使用MVVM、如何使用,个人觉得根据具体需求可以灵活处理,不用纠结于模式本身。用了MVVM,后置*.cs文件就不一定不允许写任何代码,混合着用也是没有问题的, 只要自己决的方便、代码结构清晰、维护方便即可。

二.依赖通知InotifyPropertyChanged实现

依赖通知InotifyPropertyChanged是很简单的一个接口,是View Model标配的接口,一个典型的实现(BaseNotifyPropertyChanged):  

 /// <summary> /// 实现了属性更改通知的基类 /// </summary> public class BaseNotifyPropertyChanged : System.ComponentModel.INotifyPropertyChanged { /// <summary> /// 属性值变化时发生 /// </summary> /// <param name="propertyName"></param> protected virtual void OnPropertyChanged(string propertyName) { if (this.PropertyChanged != null) this.PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName)); } public virtual event System.ComponentModel.PropertyChangedEventHandler PropertyChanged; }

然后使用方式就是这样的:  

 public int _Age; public int Age { get { return this._Age; } set { this._Age = value; base.OnPropertyChanged("Age"); } }

上面的代码有硬编码,有代码洁癖的人就不爽了,因此网上有多种解决方式,比如这篇:WPF MVVM之INotifyPropertyChanged接口的几种实现方式。本文的实现方式如下,使用表达式树:

 /// <summary> /// 属性值变化时发生 /// </summary> /// <param name="propertyName"></param> protected virtual void OnPropertyChanged<T>(Expression<Func<T>> propertyExpression) { var propertyName = (propertyExpression.Body as MemberExpression).Member.Name; this.OnPropertyChanged(propertyName); }

使用上避免了硬编码,使用示例:  

 public string _Name; public string Name { get { return this._Name; } set { this._Name = value; base.OnPropertyChanged(() => this.Name); } }

三.命令Icommand的实现

命令的实现也很简单,实现Icommand的几个接口就OK了, 考虑到使用时能更加方便,无参数RelayCommand实现:  

 /// <summary> /// 广播命令:基本ICommand实现接口 /// </summary> public class RelayCommand : ICommand { public Action ExecuteCommand { get; private set; } public Func<bool> CanExecuteCommand { get; private set; } public RelayCommand(Action executeCommand, Func<bool> canExecuteCommand) { this.ExecuteCommand = executeCommand; this.CanExecuteCommand = canExecuteCommand; } public RelayCommand(Action executeCommand) : this(executeCommand, null) { } /// <summary> /// 定义在调用此命令时调用的方法。 /// </summary> /// <param name="parameter">此命令使用的数据。如果此命令不需要传递数据,则该对象可以设置为 null。</param> public void Execute(object parameter) { if (this.ExecuteCommand != null) this.ExecuteCommand(); } /// <summary> /// 定义用于确定此命令是否可以在其当前状态下执行的方法。 /// </summary> /// <returns> /// 如果可以执行此命令,则为 true;否则为 false。 /// </returns> /// <param name="parameter">此命令使用的数据。如果此命令不需要传递数据,则该对象可以设置为 null。</param> public bool CanExecute(object parameter) { return CanExecuteCommand == null || CanExecuteCommand(); } public event EventHandler CanExecuteChanged { add { if (this.CanExecuteCommand != null) CommandManager.RequerySuggested += value; } remove { if (this.CanExecuteCommand != null) CommandManager.RequerySuggested -= value; } } }

泛型参数RelayCommand<T>的版本:  

 /// <summary> /// 广播命令:基本ICommand实现接口,带参数 /// </summary> public class RelayCommand<T> : ICommand { public Action<T> ExecuteCommand { get; private set; } public Predicate<T> CanExecuteCommand { get; private set; } public RelayCommand(Action<T> executeCommand, Predicate<T> canExecuteCommand) { this.ExecuteCommand = executeCommand; this.CanExecuteCommand = canExecuteCommand; } public RelayCommand(Action<T> executeCommand) : this(executeCommand, null) { } /// <summary> /// 定义在调用此命令时调用的方法。 /// </summary> /// <param name="parameter">此命令使用的数据。如果此命令不需要传递数据,则该对象可以设置为 null。</param> public void Execute(object parameter) { if (this.ExecuteCommand != null) this.ExecuteCommand((T)parameter); } /// <summary> /// 定义用于确定此命令是否可以在其当前状态下执行的方法。 /// </summary> /// <returns> /// 如果可以执行此命令,则为 true;否则为 false。 /// </returns> /// <param name="parameter">此命令使用的数据。如果此命令不需要传递数据,则该对象可以设置为 null。</param> public bool CanExecute(object parameter) { return CanExecuteCommand == null || CanExecuteCommand((T)parameter); } public event EventHandler CanExecuteChanged { add { if (this.CanExecuteCommand != null) CommandManager.RequerySuggested += value; } remove { if (this.CanExecuteCommand != null) CommandManager.RequerySuggested -= value; } } }

带参数和不带参数的命令XAML绑定方式:  

<core:FButton Margin="5 0 0 0" Command="{Binding ShowUserCommand}">ShowUser</core:FButton>
<core:FButton Margin="5 0 0 0" Command="{Binding SetNameCommand}" FIcon="&#xe60c;"
                          CommandParameter="{Binding Text,ElementName=txtSetName}">SetName</core:FButton>

上面是针对提供Command模式的控件示例, 但对于其他事件呢,比如MouseOver如何绑定呢?可以借用System.Windows.Interactivity.dll,其中的 Interaction 可以帮助我们实现对命令的绑定,这是在微软Blend中提供的。添加dll应用,然后添加命名空间:

xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"

 <TextBlock VerticalAlignment="Center" Margin="5 0 0 0" Text="MoseOver" x:Name="txbMessage"> <i:Interaction.Triggers> <i:EventTrigger EventName="MouseMove"> <i:InvokeCommandAction Command="{Binding MouseOverCommand}" CommandParameter="{Binding ElementName=txbMessage}"></i:InvokeCommandAction> </i:EventTrigger> </i:Interaction.Triggers> </TextBlock>

 

四.消息的实现

消息类Messenger主要目的是实现View与View Model及各个模块之间的通信。本文的消息类Messenger,参考自网络开源的实现(MVVMFoundation)。实现了松散耦合的消息通知机制,对于消息传输参数,内部使用了弱引用(WeakReference),以防止内存泄漏代码:  

 /// <summary> /// Provides loosely-coupled messaging between various colleague objects. All references to objects are stored weakly, to prevent memory leaks. /// 提供松散耦合的消息通知机制,为防止内存泄漏,所有对象都使用了弱引用(WeakReference) /// </summary> public class Messenger { #region Constructor public Messenger() { } #endregion // Constructor #region Register /// <summary> /// Registers a callback method, with no parameter, to be invoked when a specific message is broadcasted. /// 注册消息监听 /// </summary> /// <param name="message">The message to register for.</param> /// <param name="callback">The callback to be called when this message is broadcasted.</param> public void Register(string message, Action callback) { this.Register(message, callback, null); } /// <summary> /// Registers a callback method, with a parameter, to be invoked when a specific message is broadcasted. /// 注册消息监听 /// </summary> /// <param name="message">The message to register for.</param> /// <param name="callback">The callback to be called when this message is broadcasted.</param> public void Register<T>(string message, Action<T> callback) { this.Register(message, callback, typeof(T)); } void Register(string message, Delegate callback, Type parameterType) { if (String.IsNullOrEmpty(message)) throw new ArgumentException("'message' cannot be null or empty."); if (callback == null) throw new ArgumentNullException("callback"); this.VerifyParameterType(message, parameterType); _messageToActionsMap.AddAction(message, callback.Target, callback.Method, parameterType); } [Conditional("DEBUG")] void VerifyParameterType(string message, Type parameterType) { Type previouslyRegisteredParameterType = null; if (_messageToActionsMap.TryGetParameterType(message, out previouslyRegisteredParameterType)) { if (previouslyRegisteredParameterType != null && parameterType != null) { if (!previouslyRegisteredParameterType.Equals(parameterType)) throw new InvalidOperationException(string.Format( "The registered action's parameter type is inconsistent with the previously registered actions for message '{0}'./nExpected: {1}/nAdding: {2}", message, previouslyRegisteredParameterType.FullName, parameterType.FullName)); } else { // One, or both, of previouslyRegisteredParameterType or callbackParameterType are null. if (previouslyRegisteredParameterType != parameterType) // not both null? { throw new TargetParameterCountException(string.Format( "The registered action has a number of parameters inconsistent with the previously registered actions for message /"{0}/"./nExpected: {1}/nAdding: {2}", message, previouslyRegisteredParameterType == null ? 0 : 1, parameterType == null ? 0 : 1)); } } } } #endregion // Register #region Notify /// <summary> /// Notifies all registered parties that a message is being broadcasted. /// 发送消息通知,触发监听执行 /// </summary> /// <param name="message">The message to broadcast.</param> /// <param name="parameter">The parameter to pass together with the message.</param> public void Notify(string message, object parameter) { if (String.IsNullOrEmpty(message)) throw new ArgumentException("'message' cannot be null or empty."); Type registeredParameterType; if (_messageToActionsMap.TryGetParameterType(message, out registeredParameterType)) { if (registeredParameterType == null) throw new TargetParameterCountException(string.Format("Cannot pass a parameter with message '{0}'. Registered action(s) expect no parameter.", message)); } var actions = _messageToActionsMap.GetActions(message); if (actions != null) actions.ForEach(action => action.DynamicInvoke(parameter)); } /// <summary> /// Notifies all registered parties that a message is being broadcasted. /// 发送消息通知,触发监听执行 /// </summary> /// <param name="message">The message to broadcast.</param> public void Notify(string message) { if (String.IsNullOrEmpty(message)) throw new ArgumentException("'message' cannot be null or empty."); Type registeredParameterType; if (_messageToActionsMap.TryGetParameterType(message, out registeredParameterType)) { if (registeredParameterType != null) throw new TargetParameterCountException(string.Format("Must pass a parameter of type {0} with this message. Registered action(s) expect it.", registeredParameterType.FullName)); } var actions = _messageToActionsMap.GetActions(message); if (actions != null) actions.ForEach(action => action.DynamicInvoke()); } #endregion // NotifyColleauges #region MessageToActionsMap [nested class] /// <summary> /// This class is an implementation detail of the Messenger class. /// </summary> private class MessageToActionsMap { #region Constructor internal MessageToActionsMap() { } #endregion // Constructor #region AddAction /// <summary> /// Adds an action to the list. /// </summary> /// <param name="message">The message to register.</param> /// <param name="target">The target object to invoke, or null.</param> /// <param name="method">The method to invoke.</param> /// <param name="actionType">The type of the Action delegate.</param> internal void AddAction(string message, object target, MethodInfo method, Type actionType) { if (message == null) throw new ArgumentNullException("message"); if (method == null) throw new ArgumentNullException("method"); lock (_map) { if (!_map.ContainsKey(message)) _map[message] = new List<WeakAction>(); _map[message].Add(new WeakAction(target, method, actionType)); } } #endregion // AddAction #region GetActions /// <summary> /// Gets the list of actions to be invoked for the specified message /// </summary> /// <param name="message">The message to get the actions for</param> /// <returns>Returns a list of actions that are registered to the specified message</returns> internal List<Delegate> GetActions(string message) { if (message == null) throw new ArgumentNullException("message"); List<Delegate> actions; lock (_map) { if (!_map.ContainsKey(message)) return null; List<WeakAction> weakActions = _map[message]; actions = new List<Delegate>(weakActions.Count); for (int i = weakActions.Count - 1; i > -1; --i) { WeakAction weakAction = weakActions[i]; if (weakAction == null) continue; Delegate action = weakAction.CreateAction(); if (action != null) { actions.Add(action); } else { // The target object is dead, so get rid of the weak action. weakActions.Remove(weakAction); } } // Delete the list from the map if it is now empty. if (weakActions.Count == 0) _map.Remove(message); } // Reverse the list to ensure the callbacks are invoked in the order they were registered. actions.Reverse(); return actions; } #endregion // GetActions #region TryGetParameterType /// <summary> /// Get the parameter type of the actions registered for the specified message. /// </summary> /// <param name="message">The message to check for actions.</param> /// <param name="parameterType"> /// When this method returns, contains the type for parameters /// for the registered actions associated with the specified message, if any; otherwise, null. /// This will also be null if the registered actions have no parameters. /// This parameter is passed uninitialized. /// </param> /// <returns>true if any actions were registered for the message</returns> internal bool TryGetParameterType(string message, out Type parameterType) { if (message == null) throw new ArgumentNullException("message"); parameterType = null; List<WeakAction> weakActions; lock (_map) { if (!_map.TryGetValue(message, out weakActions) || weakActions.Count == 0) return false; } parameterType = weakActions[0].ParameterType; return true; } #endregion // TryGetParameterType #region Fields // Stores a hash where the key is the message and the value is the list of callbacks to invoke. readonly Dictionary<string, List<WeakAction>> _map = new Dictionary<string, List<WeakAction>>(); #endregion // Fields } #endregion // MessageToActionsMap [nested class] #region WeakAction [nested class] /// <summary> /// This class is an implementation detail of the MessageToActionsMap class. /// </summary> private class WeakAction { #region Constructor /// <summary> /// Constructs a WeakAction. /// </summary> /// <param name="target">The object on which the target method is invoked, or null if the method is static.</param> /// <param name="method">The MethodInfo used to create the Action.</param> /// <param name="parameterType">The type of parameter to be passed to the action. Pass null if there is no parameter.</param> internal WeakAction(object target, MethodInfo method, Type parameterType) { if (target == null) { _targetRef = null; } else { _targetRef = new WeakReference(target); } _method = method; this.ParameterType = parameterType; if (parameterType == null) { _delegateType = typeof(Action); } else { _delegateType = typeof(Action<>).MakeGenericType(parameterType); } } #endregion // Constructor #region CreateAction /// <summary> /// Creates a "throw away" delegate to invoke the method on the target, or null if the target object is dead. /// </summary> internal Delegate CreateAction() { // Rehydrate into a real Action object, so that the method can be invoked. if (_targetRef == null) { return Delegate.CreateDelegate(_delegateType, _method); } else { try { object target = _targetRef.Target; if (target != null) return Delegate.CreateDelegate(_delegateType, target, _method); } catch { } } return null; } #endregion // CreateAction #region Fields internal readonly Type ParameterType; readonly Type _delegateType; readonly MethodInfo _method; readonly WeakReference _targetRef; #endregion // Fields } #endregion // WeakAction [nested class] #region Fields readonly MessageToActionsMap _messageToActionsMap = new MessageToActionsMap(); #endregion // Fields }

在后面的示例中有简单使用。

五.简单MVVM示例

5.1 View Model定义实现

实现一个UserViewModel,定义了两个通知属性,3个命令,用于在XAML中实现不同的命令绑定处理,还注册了一个消息,代码:  

 public class UserViewModel : BaseNotifyPropertyChanged { public string _Name; public string Name { get { return this._Name; } set { this._Name = value; base.OnPropertyChanged(() => this.Name); } } public int _Age; public int Age { get { return this._Age; } set { this._Age = value; base.OnPropertyChanged("Age"); } } public RelayCommand<string> SetNameCommand { get; private set; } public RelayCommand ShowUserCommand { get; private set; } public RelayCommand<FrameworkElement> MouseOverCommand { get; private set; } public UserViewModel() { this.SetNameCommand = new RelayCommand<string>(this.SetName); this.ShowUserCommand = new RelayCommand(this.ShowUser); this.MouseOverCommand = new RelayCommand<FrameworkElement>(this.MouseOver); Page_MVVM.GlobalMessager.Register("123", () => { MessageBoxX.Info("我是处理123消息的!"); }); } public void SetName(string name) { if (MessageBoxX.Question(string.Format("要把Name值由[{0}]修改为[{1}]吗?", this.Name, name))) { this.Name = name; } } public void ShowUser() { MessageBoxX.Info(this.Name + "---" + this.Age); } public void MouseOver(FrameworkElement tb) { MessageBoxX.Info("我好像摸到了" + tb.Name); } }

5.2 测试页面Page_MVVM.xaml

创建一个测试页面Page_MVVM,后置代码如下,在构造函数里注入View Model,在一个按钮事件里发送消息:  

 public partial class Page_MVVM : Page { public static Messenger GlobalMessager = new Messenger(); public Page_MVVM() { InitializeComponent(); //set vm UserViewModel uvm = new UserViewModel(); uvm.Name = "kwong"; uvm.Age = 30; this.DataContext = uvm; } private void ButtonBase_OnClick(object sender, RoutedEventArgs e) { GlobalMessager.Notify("123"); } }

完整XAML代码:  

<Page x:Class="Kwong.Framework.WPFTest.Page_MVVM" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:core="clr-namespace:XLY.Framework.Controls;assembly=XLY.Framework.Controls" xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" mc:Ignorable="d" d:DesignHeight="600" d:DesignWidth="800" Title="Page_MVVM"> <Page.Resources> <Style TargetType="StackPanel"> <Setter Property="Height" Value="80"/> <Setter Property="Margin" Value="3"/> <Setter Property="Orientation" Value="Horizontal"/> <Setter Property="Background" Value="{StaticResource WindowBackground}"/> </Style> </Page.Resources> <StackPanel Style="{x:Null}"> <StackPanel > <TextBox Height="30" Width="240" Text="{Binding Name,UpdateSourceTrigger=PropertyChanged}" Margin="5 0 0 0" core:ControlAttachProperty.Label="{Binding Name.Length,Mode=OneWay}" Style="{StaticResource LabelTextBox}"/> <TextBox Height="30" Width="240" Text="{Binding Age}" core:ControlAttachProperty.Label="Age:" Style="{StaticResource LabelTextBox}" Margin="5 0 0 0"/> </StackPanel> <StackPanel> <core:FButton Margin="5 0 0 0" Command="{Binding ShowUserCommand}">ShowUser</core:FButton> <core:FButton Margin="5 0 0 0" FIcon="&#xe61c;" Width="125" Click="ButtonBase_OnClick">Send Message</core:FButton> </StackPanel> <StackPanel> <TextBox Height="30" Width="240" x:Name="txtSetName" core:ControlAttachProperty.Label="Name-" Margin="5 0 0 0" Style="{StaticResource LabelTextBox}"></TextBox> <core:FButton Margin="5 0 0 0" Command="{Binding SetNameCommand}" FIcon="&#xe60c;" CommandParameter="{Binding Text,ElementName=txtSetName}">SetName</core:FButton> </StackPanel> <StackPanel> <TextBlock VerticalAlignment="Center" Margin="5 0 0 0" Text="MoseOver" x:Name="txbMessage"> <i:Interaction.Triggers> <i:EventTrigger EventName="MouseMove"> <i:InvokeCommandAction Command="{Binding MouseOverCommand}" CommandParameter="{Binding ElementName=txbMessage}"></i:InvokeCommandAction> </i:EventTrigger> </i:Interaction.Triggers> </TextBlock> </StackPanel> </StackPanel></Page>

5.3 效果

 

 附录:参考引用

WPF自定义控件与样式(1)-矢量字体图标(iconfont)

WPF自定义控件与样式(2)-自定义按钮FButton

WPF自定义控件与样式(3)-TextBox & RichTextBox & PasswordBox样式、水印、Label标签、功能扩展

WPF自定义控件与样式(4)-CheckBox/RadioButton自定义样式

WPF自定义控件与样式(5)-Calendar/DatePicker日期控件自定义样式及扩展

WPF自定义控件与样式(6)-ScrollViewer与ListBox自定义样式

WPF自定义控件与样式(7)-列表控件DataGrid与ListView自定义样式

WPF自定义控件与样式(8)-ComboBox与自定义多选控件MultComboBox

WPF自定义控件与样式(9)-树控件TreeView与菜单Menu-ContextMenu

WPF自定义控件与样式(10)-进度控件ProcessBar自定义样 

WPF自定义控件与样式(11)-等待/忙/正在加载状态-控件实现

WPF自定义控件与样式(12)-缩略图ThumbnailImage /gif动画图/图片列表

WPF自定义控件与样式(13)-自定义窗体Window & 自适应内容大小消息框MessageBox

 

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