Mvvm模式学习

mvvm模式.先让xaml页面与xaml.cs分离。

原来是双击button生成个事件，添加代码，按钮的功能完成。要使页面与代码分离，最起码得把button事件的处理代码从xaml.cs文件中弄出去吧。

原来是直接双击，后台生成。现在不能双击了。麻烦但是有用。不经革命之痛苦，怎得革命之幸福。

找个代码，改改理解理解吧。发现要实现点击得数据绑定。

        <Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top"  Command="{Binding Path=ShowCommand}" Width="75" Margin="331,224,0,0"/>

既然是绑定就得有数据上下文。查找发现有

<Grid.DataContext>
           <local:ShowViewModel />
       </Grid.DataContext>

那么就得有xmlns:local="clr-namespace:mccmlearn.ViewModel"

页面代码：

<Window x:Class="mccmlearn.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:local="clr-namespace:mccmlearn.ViewModel"Title="MainWindow" Height="350" Width="525"><Grid><Grid.DataContext><local:ShowViewModel /></Grid.DataContext><Button Content="Button" HorizontalAlignment="Left" VerticalAlignment="Top" Command="{Binding Path=ShowCommand}" Width="75" Margin="331,224,0,0"/></Grid> </Window>

后台代码不用贴了因为什么也没有。

这是项目结构，看viewmodel中的ShowViewModel.cs

 

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Input; using mccmlearn.Commands;namespace mccmlearn.ViewModel {internal class ShowViewModel{private DelegateCommand showCommand;public ICommand ShowCommand{get{if (showCommand == null)showCommand = new DelegateCommand(new Action(ShowExecuted), new Func<bool>(ShowCanExecute));return showCommand;}}private bool ShowCanExecute(){return true;}private void ShowExecuted(){System.Windows.MessageBox.Show("dd");}} }

下面是DelegateCommand类，从网上找的，

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows.Input;namespace mccmlearn.Commands {/// <summary>/// This class allows delegating the commanding logic to methods passed as parameters,/// and enables a View to bind commands to objects that are not part of the element tree./// </summary>public class DelegateCommand : ICommand{#region Constructors/// <summary>/// Constructor/// </summary>public DelegateCommand(Action executeMethod): this(executeMethod, null, false){}/// <summary>/// Constructor/// </summary>public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod): this(executeMethod, canExecuteMethod, false){}/// <summary>/// Constructor/// </summary>public DelegateCommand(Action executeMethod, Func<bool> canExecuteMethod, bool isAutomaticRequeryDisabled){if (executeMethod == null){throw new ArgumentNullException("executeMethod");}_executeMethod = executeMethod;_canExecuteMethod = canExecuteMethod;_isAutomaticRequeryDisabled = isAutomaticRequeryDisabled;}#endregion#region Public Methods/// <summary>/// Method to determine if the command can be executed/// </summary>public bool CanExecute(){if (_canExecuteMethod != null){return _canExecuteMethod();}return true;}/// <summary>/// Execution of the command/// </summary>public void Execute(){if (_executeMethod != null){_executeMethod();}}/// <summary>/// Property to enable or disable CommandManager's automatic requery on this command/// </summary>public bool IsAutomaticRequeryDisabled{get{return _isAutomaticRequeryDisabled;}set{if (_isAutomaticRequeryDisabled != value){if (value){CommandManagerHelper.RemoveHandlersFromRequerySuggested(_canExecuteChangedHandlers);}else{CommandManagerHelper.AddHandlersToRequerySuggested(_canExecuteChangedHandlers);}_isAutomaticRequeryDisabled = value;}}}/// <summary>/// Raises the CanExecuteChaged event/// </summary>public void RaiseCanExecuteChanged(){OnCanExecuteChanged();}/// <summary>/// Protected virtual method to raise CanExecuteChanged event/// </summary>protected virtual void OnCanExecuteChanged(){CommandManagerHelper.CallWeakReferenceHandlers(_canExecuteChangedHandlers);}#endregion#region ICommand Members/// <summary>/// ICommand.CanExecuteChanged implementation/// </summary>public event EventHandler CanExecuteChanged{add{if (!_isAutomaticRequeryDisabled){CommandManager.RequerySuggested += value;}CommandManagerHelper.AddWeakReferenceHandler(ref _canExecuteChangedHandlers, value, 2);}remove{if (!_isAutomaticRequeryDisabled){CommandManager.RequerySuggested -= value;}CommandManagerHelper.RemoveWeakReferenceHandler(_canExecuteChangedHandlers, value);}}bool ICommand.CanExecute(object parameter){return CanExecute();}void ICommand.Execute(object parameter){Execute();}#endregion#region Dataprivate readonly Action _executeMethod = null;private readonly Func<bool> _canExecuteMethod = null;private bool _isAutomaticRequeryDisabled = false;private List<WeakReference> _canExecuteChangedHandlers;#endregion}/// <summary>/// This class allows delegating the commanding logic to methods passed as parameters,/// and enables a View to bind commands to objects that are not part of the element tree./// </summary>/// <typeparam name="T">Type of the parameter passed to the delegates</typeparam>public class DelegateCommand<T> : ICommand{#region Constructors/// <summary>/// Constructor/// </summary>public DelegateCommand(Action<T> executeMethod): this(executeMethod, null, false){}/// <summary>/// Constructor/// </summary>public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod): this(executeMethod, canExecuteMethod, false){}/// <summary>/// Constructor/// </summary>public DelegateCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod, bool isAutomaticRequeryDisabled){if (executeMethod == null){throw new ArgumentNullException("executeMethod");}_executeMethod = executeMethod;_canExecuteMethod = canExecuteMethod;_isAutomaticRequeryDisabled = isAutomaticRequeryDisabled;}#endregion#region Public Methods/// <summary>/// Method to determine if the command can be executed/// </summary>public bool CanExecute(T parameter){if (_canExecuteMethod != null){return _canExecuteMethod(parameter);}return true;}/// <summary>/// Execution of the command/// </summary>public void Execute(T parameter){if (_executeMethod != null){_executeMethod(parameter);}}/// <summary>/// Raises the CanExecuteChaged event/// </summary>public void RaiseCanExecuteChanged(){OnCanExecuteChanged();}/// <summary>/// Protected virtual method to raise CanExecuteChanged event/// </summary>protected virtual void OnCanExecuteChanged(){CommandManagerHelper.CallWeakReferenceHandlers(_canExecuteChangedHandlers);}/// <summary>/// Property to enable or disable CommandManager's automatic requery on this command/// </summary>public bool IsAutomaticRequeryDisabled{get{return _isAutomaticRequeryDisabled;}set{if (_isAutomaticRequeryDisabled != value){if (value){CommandManagerHelper.RemoveHandlersFromRequerySuggested(_canExecuteChangedHandlers);}else{CommandManagerHelper.AddHandlersToRequerySuggested(_canExecuteChangedHandlers);}_isAutomaticRequeryDisabled = value;}}}#endregion#region ICommand Members/// <summary>/// ICommand.CanExecuteChanged implementation/// </summary>public event EventHandler CanExecuteChanged{add{if (!_isAutomaticRequeryDisabled){CommandManager.RequerySuggested += value;}CommandManagerHelper.AddWeakReferenceHandler(ref _canExecuteChangedHandlers, value, 2);}remove{if (!_isAutomaticRequeryDisabled){CommandManager.RequerySuggested -= value;}CommandManagerHelper.RemoveWeakReferenceHandler(_canExecuteChangedHandlers, value);}}bool ICommand.CanExecute(object parameter){// if T is of value type and the parameter is not// set yet, then return false if CanExecute delegate// exists, else return trueif (parameter == null &&typeof(T).IsValueType){return (_canExecuteMethod == null);}return CanExecute((T)parameter);}void ICommand.Execute(object parameter){Execute((T)parameter);}#endregion#region Dataprivate readonly Action<T> _executeMethod = null;private readonly Func<T, bool> _canExecuteMethod = null;private bool _isAutomaticRequeryDisabled = false;private List<WeakReference> _canExecuteChangedHandlers;#endregion}/// <summary>/// This class contains methods for the CommandManager that help avoid memory leaks by/// using weak references./// </summary>internal class CommandManagerHelper{internal static void CallWeakReferenceHandlers(List<WeakReference> handlers){if (handlers != null){// Take a snapshot of the handlers before we call out to them since the handlers// could cause the array to me modified while we are reading it. EventHandler[] callees = new EventHandler[handlers.Count];int count = 0;for (int i = handlers.Count - 1; i >= 0; i--){WeakReference reference = handlers[i];EventHandler handler = reference.Target as EventHandler;if (handler == null){// Clean up old handlers that have been collected handlers.RemoveAt(i);}else{callees[count] = handler;count++;}}// Call the handlers that we snapshottedfor (int i = 0; i < count; i++){EventHandler handler = callees[i];handler(null, EventArgs.Empty);}}}internal static void AddHandlersToRequerySuggested(List<WeakReference> handlers){if (handlers != null){foreach (WeakReference handlerRef in handlers){EventHandler handler = handlerRef.Target as EventHandler;if (handler != null){CommandManager.RequerySuggested += handler;}}}}internal static void RemoveHandlersFromRequerySuggested(List<WeakReference> handlers){if (handlers != null){foreach (WeakReference handlerRef in handlers){EventHandler handler = handlerRef.Target as EventHandler;if (handler != null){CommandManager.RequerySuggested -= handler;}}}}internal static void AddWeakReferenceHandler(ref List<WeakReference> handlers, EventHandler handler){AddWeakReferenceHandler(ref handlers, handler, -1);}internal static void AddWeakReferenceHandler(ref List<WeakReference> handlers, EventHandler handler, int defaultListSize){if (handlers == null){handlers = (defaultListSize > 0 ? new List<WeakReference>(defaultListSize) : new List<WeakReference>());}handlers.Add(new WeakReference(handler));}internal static void RemoveWeakReferenceHandler(List<WeakReference> handlers, EventHandler handler){if (handlers != null){for (int i = handlers.Count - 1; i >= 0; i--){WeakReference reference = handlers[i];EventHandler existingHandler = reference.Target as EventHandler;if ((existingHandler == null) || (existingHandler == handler)){// Clean up old handlers that have been collected// in addition to the handler that is to be removed. handlers.RemoveAt(i);}}}}} }

这样就实现了按钮的事件，没有写在.xaml.cs里面。

转载于:https://www.cnblogs.com/shiyue/archive/2013/01/24/2874736.html

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