一种应用方法是使用依赖项属性代替INotifyPropertyChanged接口，将界面绑定的数据源属性声明为依赖项属性，就可以自动更新到界面了，使用了wpf的内置机制，之前有一篇文章写了一个例子。
今天写的应用是重写一个控件，新空间使用依赖项属性来扩展wpf内置控件的功能，不过我的这个控件更多是为了方便使用，类似于是老控件的一个对象，只用于某种特殊的表示方式，来源于一道面试题，两个comboBox，一个是省名称，一个是市名称，当省的comboBox选项改变时，市comboBox列表也随之改变，用依赖项属性实现。
首先来展示一下，如果不使用依赖项属性，正常的做法
声明两个comboBox，一个是省，一个是市
<ComboBox Grid.Row="0" Name="ProvienceComboBox" Height="30" ItemsSource="{Binding Path=Proviences}" SelectionChanged="ComboBox_SelectionChanged"
SelectedValuePath="Id" DisplayMemberPath="Name" SelectedIndex="0">
</ComboBox>
<ComboBox Grid.Row="1" Name="CityComboBox" Height="30" SelectedIndex="0" SelectedValuePath="Id" DisplayMemberPath="Name">
</ComboBox>
后台数据结构：
public class NotifyPropertyChangeBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChangedEventArgs e = new PropertyChangedEventArgs(propertyName);
PropertyChanged(this,e);
}
}
}
//这个省数据使用依赖项属性实现，是之前提到的依赖项属性的一种应用 方法
public class ProvienceInfo : DependencyObject
{
public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name",typeof(string),typeof(ProvienceInfo));
public ProvienceInfo(string s,int id)
{
Name = s;
this.id = id;
}
private int id;
public int Id
{
set
{
if (id != value)
{
id = value;
}
}
get
{
return id;
}
}
public string Name
{
set
{
//if (name != value)
{
SetValue(NameProperty,value);
}
}
get
{
return GetValue(NameProperty).ToString();
}
}
private CityList citys;
public CityList Citys
{
get
{
return citys;
}
set
{
if (citys != value)
{
citys = value;
}
}
}
}
//市使用notify接口实现
public class CityInfo : NotifyPropertyChangeBase
{
public CityInfo(string name)
{
this.name = name;
}
private string name;
public string Name
{
set
{
if (name != value)
{
name = value;
OnPropertyChanged("Name");
}
}
get
{
return name;
}
}
}
public class ProvienceList : ObservableCollection<ProvienceInfo>
{
}
public class CityList : ObservableCollection<CityInfo>
{
}
专门为UI提供数据的数据类
public class Data
{
//假数据
public Data()
{
proviences = new ProvienceList();
citys = new CityList();
string[] s = { "hebei","henan","shandong" };
string[][] cityArrar = new string[3][];
string[] hebeicity= { "shijiazhuang","baoding","tangshan" };
string[] henancity = { "zhengzhou","pingdingshan" };
string[] shandongcity = { "qingdao","jinan" };
cityArrar[0] = hebeicity;
cityArrar[1] = henancity;
cityArrar[2] = shandongcity;
for (int i = 0; i < 3; i++)
{
ProvienceInfo pi = new ProvienceInfo(s[i],i);
CityList cl = new CityList();
proviences.Add(pi);
for (int j = 0; j < cityArrar[i].Length; j++)
{
cl.Add(new CityInfo(cityArrar[i][j]));
}
pi.Citys = cl;
}
}
ProvienceList proviences;
public ProvienceList Proviences
{
get
{
return proviences;
}
set
{
proviences = value;
}
}
}
后台的数据源绑定
public MainWindow()
{
InitializeComponent();
data = new Data();
this.DataContext = data; //给控件设置datacontext
}
//当省级的comboBox选项改变的时候变更市级comboBox的数据源
private void ComboBox_SelectionChanged(object sender,SelectionChangedEventArgs e)
{
ComboBox cb = sender as ComboBox;
object o = cb.SelectedValue;
CityComboBox.ItemsSource = (cb.SelectedItem as ProvienceInfo).Citys;
CityComboBox.SelectedIndex = 0;
}
这样就可以实现功能了。
如果使用依赖项属性，我创建了一个新类，扩展comboBox，该类中有一个citylist属性，用户只需要给改属性赋值或绑定，就可以显示
public class MyComboBox : ComboBox
{
public static readonly DependencyProperty cityListProperty = DependencyProperty.Register("cityList",typeof(CityList),typeof(MyComboBox),new PropertyMetadata(null,MyPropertyChangedCallback));
static void MyPropertyChangedCallback(DependencyObject d,DependencyPropertyChangedEventArgs e)
{
MyComboBox m = d as MyComboBox;
if (m != null)
{
m.ItemsSource = m.cityList; //实际上citylist只是将itemsource封装起来了
m.SelectedIndex = 0;
}
}
public MyComboBox()
{
this.DisplayMemberPath = "Name"; //限制了只能显示city的name，或者还有其他好的办法可以进行拓展？
}
public CityList cityList
{
get
{
return (CityList)GetValue(cityListProperty);
}
set
{
SetValue(cityListProperty,value);
}
}
}
前台xaml，只需设置citylist
<local:MyComboBox x:Name="myComboBox" Grid.Row="3" cityList="{Binding Path=Citys}" SelectedIndex="0"/>
数据源中添加一个citys的数据，因为mycomboBox中需要绑定，此处省略。
当省的选项改变时，只需改变mycomboBox的citylist
private void ComboBox_SelectionChanged(object sender,SelectionChangedEventArgs e)
{
ComboBox cb = sender as ComboBox;
myComboBox.cityList = (cb.SelectedItem as ProvienceInfo).Citys;
}
此处依赖项属性的应用只是更方便的为用户提供功能，并没有扩展，要想真正扩展控件的功能，恐怕要做的还有很多。
不知此处的应用是否正确，合理，符合依赖项属性的目的，如有高见，请不吝赐教。