MVVM MVC

在WPF的MVVM模式中，View和ViewModel之间数据和命令的关联都是通过绑定实现的，绑定后View和ViewModel并不产生直接的依赖。具体就是View中出现数据变化时会尝试修改绑定的目标。同样View执行命令时也会去寻找绑定的Command并执行。反过来，ViewModel在Property发生改变时会发个通知说“名字叫XXX的Property改变了，你们这些View中谁绑定了XXX也要跟着变啊!”，至于有没有View收到是不是做出变化也不关心。ViewModel中的Command脱离View就更简单了，因为Command在执行操作过程中操作数据时，根本不需要操作View中的数据，只需要操作ViewModel中的Property就可以了，Property的变化通过绑定就可以反映到View上。这样在测试Command时也不需要View的参与。这也是我在接触WPF初期时根本理解不了的所谓数据驱动。

这样一来ViewMode可以在完全没有View的情况下测试，View也可以在完全没有ViewModel的情况下测试(当然只是测试界面布局和动画等业务无关的内容)。

1、App中的代码：

public App()

{

    CalculatorView view = new CalculatorView();

    view.DataContext = new CalculatorViewModel();

    view.Show();

}

2、Model层中CauculatorModel的代码

class CauculatorModel

{

     public string FirstOperand { get; set; }

     public string SecondOperand { get; set; }

     public string Operation { get; set; }

     public string Result { get; set; }

}

3、Command

public class DeletgateCommand<T>:ICommand

 {

     private readonly Action<T> _executeMethod = null;

     private readonly Func<T,bool> _canExecuteMethod = null;

     public DeletgateCommand(Action<T> executeMethod)

         : this(executeMethod, null)

     { }

     public DeletgateCommand(Action<T> executeMethod, Func<T,bool> canExecuteMethod) 

     {

         if (executeMethod == null)

             throw new ArgumentNullException("executeMetnod");

         _executeMethod = executeMethod;

         _canExecuteMethod = canExecuteMethod;

     }

     #region ICommand 成员

     /// <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);

         }

     }

     #endregion

     event EventHandler ICommand.CanExecuteChanged

     {

         add { CommandManager.RequerySuggested += value; }

         remove { CommandManager.RequerySuggested -= value; }

     }

     #region ICommand 成员

     public bool CanExecute(object parameter)

     {

         if (parameter == null && typeof(T).IsValueType)

         {

             return (_canExecuteMethod == null);

         }

         

         return CanExecute((T)parameter);

     }

     public void Execute(object parameter)

     {

         Execute((T)parameter);

     }

     #endregion

 }

4、ViewModwl层，为了简化，此处Add方法采用硬编码的形式

public class CalculatorViewModel

 {

     CauculatorModel calculatorModel;

     private DeletgateCommand<string> addCommand;

     

     public CalculatorViewModel()

     {

         calculatorModel = new CauculatorModel();

     }

     #region Public Properties

     public string FirstOperand

     {

         get {  return calculatorModel.FirstOperand;  }

         set { calculatorModel.FirstOperand = value;  }

     }

     public string SecondOperand

     {

         get { return calculatorModel.SecondOperand; }

         set { calculatorModel.SecondOperand = value; }

     }

     public string Operation

     {

         get { return calculatorModel.Operation; }

         set { calculatorModel.Operation = value; }

     }

     public string Result

     {

         get { return calculatorModel.Result; }

         set { calculatorModel.Result = value; }

     }

     #endregion

     public ICommand AddCommand

     {

         get

         {

             if (addCommand == null)

             {

                 addCommand = new DeletgateCommand<string>(Add, CanAdd);

             }

             return addCommand;

         }

     }

        

     public  void Add(string x)

     {

         FirstOperand = x;

         SecondOperand = x;

         Result = (double.Parse(FirstOperand) + double.Parse(SecondOperand)).ToString();

         Operation = "+";

         MessageBox.Show( FirstOperand+ Operation +SecondOperand +"=" + Result);

     }

     private static bool CanAdd(string num)

     {

         return true;

     }

 }

ViewModelBase中的代码：

public abstract class ViewModelBase : INotifyPropertyChanged

 {

     public event PropertyChangedEventHandler PropertyChanged;

     protected void OnPropertyChanged(string propertyName)

     {

         PropertyChangedEventHandler handler = PropertyChanged;

         if (handler != null)

         {

             handler(this, new PropertyChangedEventArgs(propertyName));

         }

     }

 }

5、View层

<Grid>   

       <TextBox  Height="23" Margin="12,63,0,0" Name="textBox1" VerticalAlignment="Top" HorizontalAlignment="Left"  Width="120" />

       <Label Margin="12,25,95,0" Name="label2" Height="32" VerticalAlignment="Top">请输入x的值！ x+x=? </Label>

       <Button Height="23" Command="{Binding AddCommand}"

               CommandParameter="{Binding ElementName=textBox1,Path=Text}"   HorizontalAlignment="Left" Margin="12,102,0,0" Name="button1" VerticalAlignment="Top" Width="75">

           确定</Button>

   </Grid>

CommandParameter里传递的是一个参数，当然可以传递多个参数。