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。