xaml mvvm(2)之属性绑定

通过微软INotifyPropertyChanged接口，可以实现对UI实时更新，不管是数据源或者目标对象，可以实现相互通知。

下面我们根据INotifyPropertyChanged编写一个扩展类。该类是基于C#5.0特性，这里我们介绍一下System.Runtime.CompilerServices命名空间下的CallerMemberName特性，当RaisePropertyChanged的属性名称参数为空，而通过编译器可以智能加上，可以通过反编译工具知晓，这点改进这点很人性化。注：如果开发版本framework 4.0，则需要安装KB2468871补丁或者更新framework 4.0以上版本。

为这个扩展类添加命名空间如下。

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Linq.Expressions;
 using System.Reflection;
 using System.Runtime.CompilerServices;

 public class ObservableObject : INotifyPropertyChanged
 {
     public event PropertyChangedEventHandler PropertyChanged;
     protected PropertyChangedEventHandler PropertyChangedHandler
     {
         get
         {
             return this.PropertyChanged;
         }
     }
     [Conditional("DEBUG"), DebuggerStepThrough]
     public void VerifyPropertyName(string propertyName)
     {
         Type type = base.GetType();
         if (!string.IsNullOrEmpty(propertyName) && type.GetTypeInfo().GetDeclaredProperty(propertyName) == null)
         {
             throw new ArgumentException("Property not found", propertyName);
         }
     }
     protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
     {
         PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
         if (propertyChanged != null)
         {
             propertyChanged(this, new PropertyChangedEventArgs(propertyName));
         }
     }
     protected virtual void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpression)
     {
         PropertyChangedEventHandler propertyChanged = this.PropertyChanged;
         if (propertyChanged != null)
         {
             string propertyName = ObservableObject.GetPropertyName<T>(propertyExpression);
             propertyChanged(this, new PropertyChangedEventArgs(propertyName));
         }
     }
     protected static string GetPropertyName<T>(Expression<Func<T>> propertyExpression)
     {
         if (propertyExpression == null)
         {
             throw new ArgumentNullException("propertyExpression");
         }
         MemberExpression memberExpression = propertyExpression.Body as MemberExpression;
         if (memberExpression == null)
         {
             throw new ArgumentException("Invalid argument", "propertyExpression");
         }
         PropertyInfo propertyInfo = memberExpression.Member as PropertyInfo;
         if (propertyInfo == null)
         {
             throw new ArgumentException("Argument is not a property", "propertyExpression");
         }
         return propertyInfo.Name;
     }
     protected bool Set<T>(Expression<Func<T>> propertyExpression, ref T field, T newValue)
     {
         if (EqualityComparer<T>.Default.Equals(field, newValue))
         {
             return false;
         }
         field = newValue;
         this.RaisePropertyChanged<T>(propertyExpression);
         return true;
     }
     protected bool Set<T>(string propertyName, ref T field, T newValue)
     {
         if (EqualityComparer<T>.Default.Equals(field, newValue))
         {
             return false;
         }
         field = newValue;
         this.RaisePropertyChanged(propertyName);
         return true;
     }
     protected bool Set<T>(ref T field, T newValue, [CallerMemberName] string propertyName = null)
     {
         return this.Set<T>(propertyName, ref field, newValue);
     }
 }

下面我们来继承这个类编写一个Animal类对象。在这里我们用到RaisePropertyChanged三种不同的实现方式，达到一样的绑定效果。

 public class Animal : ObservableObject
 {
     private string m_Cat;
     public string Cat
     {
         get { return m_Cat; }
         set { m_Cat = value; RaisePropertyChanged("Cat"); }
     }

     private string m_Dog;
     public string Dog
     {
         get { return m_Dog; }
         set { m_Dog = value; RaisePropertyChanged(); }
     }

     private string m_Tiger;
     public string Tiger
     {
         get { return m_Tiger; }
         set { m_Tiger = value; RaisePropertyChanged(() => this.Tiger); }
     }
 }

下面我们来建立model视图类。在该类中用的事件绑定和model对象实现，我们会在后续介绍。

 public class MainPageViewModel : Core.ViewModelBase
 {
     public MainPageViewModel()
     {
         MyAnimal = new Animal();
     }

     private Animal m_MyAnimal;
     public Animal MyAnimal
     {
         get { return m_MyAnimal; }
         set { m_MyAnimal = value; RaisePropertyChanged("MyAnimal"); }
     }

     public ICommand OKCommand
     {
         get
         {
             return new RelayCommand(() =>
             {
                 MyAnimal.Dog = "eating";
                 MyAnimal.Cat = "sleeping";
                 MyAnimal.Tiger = "hungry";
             });
         }
     }
 }

前台xaml。

 <Grid DataContext="{Binding Path=MainPageViewModel}">
     <StackPanel>
         <StackPanel Orientation="Horizontal">
             <TextBlock FontSize="" Text="cat is:" />
             <TextBlock FontSize="" Text="{Binding MyAnimal.Cat}" />
         </StackPanel>
         <StackPanel Orientation="Horizontal">
             <TextBlock FontSize="" Text="dog is:" />
             <TextBlock FontSize="" Text="{Binding MyAnimal.Dog}" />
         </StackPanel>
         <StackPanel Orientation="Horizontal">
             <TextBlock FontSize="" Text="Tiger is:" />
             <TextBlock FontSize="" Text="{Binding MyAnimal.Tiger}" />
         </StackPanel>
         <Button Width="" Content="OK" Command="{Binding OKCommand}" />
     </StackPanel>
 </Grid>

运行效果。