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。

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 Data

        private 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 true
            if (parameter == null &&
                typeof(T).IsValueType)
            {
                return (_canExecuteMethod == null);
            }
            return CanExecute((T)parameter);
        }

        void ICommand.Execute(object parameter)
        {
            Execute((T)parameter);
        }

        #endregion

        #region Data

        private 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 snapshotted
                for (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。

posted @ 2013-01-24 13:07 向阳生长阅读(389) 评论(0) 编辑收藏举报

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