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[Silverlight入门系列]使用MVVM模式(4):Prism的NotificationObject自动实现INotifyPropertyChanged接

    博客分类:
  • MVVM
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上一篇写了Model的INotifyPropertyChanged接口实现,在Prism中有一个NotificationObject自动实现了这个接口,位于Microsoft.Practices.Prism.ViewModel命名空间下。也就是说,Prism推荐ViewModel继承这个NotificationObject类来自动实现INotifyPropertyChanged接口。看看NotificationObject都有啥:

1 public abstract class NotificationObject : INotifyPropertyChanged 2 { 3 protected NotificationObject(); 4 5 protected void RaisePropertyChanged<T>(Expression<Func<T>> propertyExpression); 6 protected void RaisePropertyChanged(params string[] propertyNames); 7 protected virtual void RaisePropertyChanged(string propertyName); 8 }

提供了几个很方面的接口,调用更方便了,例如:

1 public string ModelName 2 { 3 get { return _ModelName; } 4 set 5 { 6 _ModelName = value; 7 8 RaisePropertyChanged("ModelName"); 9 10 } 11 }

第二个RaisePropertyChanged<T>(Expression<Func<T>> propertyExpression);是一个表达式,编译为一个Func委托,返回一个T类型。

例如可以这样用:

1 this.RaisePropertyChanged(() => this.MyDataSummary);

ViewModel的INotifyPropertyChanged接口和Model的INotifyPropertyChanged接口

ViewModel和Model它们二者都实现INotifyPropertyChanged接口并不矛盾。用途不一样。例如一个ViewModel可以包含多个其它的ViewModel,而它们有一个整体的HasChanged属性来标识是否有改变。这个时候这个整体的ViewModel的HasChanged属性就可以用整体的INotifyPropertyChanged,而局部的INotifyPropertyChanged实现了这个整体的INotifyPropertyChanged。看个例子:

1 using Microsoft.Practices.Prism.ViewModel; 2 3 public class MyViewModel3: NotificationObject 4 { 5 public MyModel MyModelData { get; set; } 6 public MyModel2 MyModelData2 { get; set; } 7 8 public bool HasChanges { get; set; } 9 public bool CanSave { get; set; } 10 11 public MyViewModel3(MyModel model, MyModel2 model2) 12 { 13 MyModelData = model; 14 MyModelData2 = model2; 15 16 model.PropertyChanged += this.OnPropertyChanged; 17 } 18 19 private void OnPropertyChanged(object sender, PropertyChangedEventArgs args) 20 { 21 if (args.PropertyName == "Name") 22 { 23 this.HasChanges = true; 24 this.RaisePropertyChanged(() => this.CanSave); 25 } 26 } 27 } 28 29 public class MyModel2 : INotifyPropertyChanged 30 { 31 public event PropertyChangedEventHandler PropertyChanged; 32 33 public int ModelID { get; set; } 34 35 private string _ModelName; 36 public string ModelName 37 { 38 get { return _ModelName; } 39 set 40 { 41 _ModelName = value; 42 43 if (PropertyChanged != null) 44 { 45 PropertyChanged(this, new PropertyChangedEventArgs("ModelName")); 46 } 47 } 48 } 49 } 50 51 public class MyModel : INotifyPropertyChanged 52 { 53 public event PropertyChangedEventHandler PropertyChanged; 54 55 public int ModelID { get; set; } 56 57 private string _ModelName; 58 public string ModelName 59 { 60 get { return _ModelName; } 61 set 62 { 63 _ModelName = value; 64 65 if (PropertyChanged != null) 66 { 67 PropertyChanged(this, new PropertyChangedEventArgs("ModelName")); 68 } 69 } 70 } 71 }

此外,Validation既可以放在Model里面也可以放在ViewModel里面,看你的规则是否简单,是否涉及业务逻辑,有的复杂的业务逻辑validation的需要调用后台service的建议放到ViewModel中去做。

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