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。

巴特西

xaml mvvm(2)之属性绑定

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