(读完此系列WPF和Silverlight的数据绑定问题你就轻松搞定 ) 1 Binding to List Data 前面都是绑定到一个对象,下面我们学习绑定到对象列表的方法。 我们还是先组织要绑定的数据,对象所对应的类还是Person,但新增了一个新类People,该类用来组织Person的列
(读完此系列wpf和silverlight的数据绑定问题你就轻松搞定
)
前面都是绑定到一个对象,下面我们学习绑定到对象列表的方法。
我们还是先组织要绑定的数据,对象所对应的类还是Person,但新增了一个新类People,该类用来组织Person的列表.代码如下:
<span>using </span>System;
<span>using </span>System.Collections.Generic;
<span>using </span>System.ComponentModel;<span>//INotifyPropertyChanged
</span><span>namespace </span>SimpleDataBinding
{
<span>class </span><span>Person </span>: <span>INotifyPropertyChanged
</span>{
<span>public event </span><span>PropertyChangedEventHandler </span>PropertyChanged;
<span>protected void </span>Notify(<span>string </span>PropName)
{
<span>if </span>(<span>this</span>.PropertyChanged != <span>null</span>)
{
PropertyChanged(<span>this</span>, <span>new </span><span>PropertyChangedEventArgs</span>(PropName));
}
}
<span>public </span>Person()
{
_Age = 0;
_name = <span>"Null"</span>;
<span>this</span>.CurrentDate = <span>DateTime</span>.Now;
}
<span>private string </span>_name;
<span>public string </span>Name
{
<span>get </span>{ <span>return </span>_name; }
<span>set
</span>{
<span>if </span>(<span>value </span>== _name)
{ <span>return</span>; }
_name = <span>value</span>;<span>//注意:不能用this.Name来赋值,如果这样形成循环调用,栈溢出
</span>Notify(<span>"Name"</span>);
}
}
<span>private int </span>_Age;
<span>public int </span>Age
{
<span>get </span>{ <span>return </span>_Age; }
<span>set
</span>{
<span>if </span>(<span>value </span>== _Age) <span>return</span>;
_Age = <span>value</span>;
Notify(<span>"Age"</span>);
}
}
<span>public </span><span>DateTime </span>CurrentDate { <span>get</span>; <span>set</span>; }
}
<strong><span><span>//People类
</span><span>class </span><span>People </span>: <span>List</span><<span>Person</span>>
{
}</span></strong>
}
登录后复制 |
注意在同一命名空间下的代码最后添加了Perople类。
我们在UI里显示的XAML如下:
<span><</span><span>Window </span><span>x</span><span>:</span><span>Class</span><span>="ListDataBinding.BindListDataTest"
</span><span>xmlns</span><span>="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
</span><span>xmlns</span><span>:</span><span>x</span><span>="http://schemas.microsoft.com/winfx/2006/xaml"
<u> </u></span><strong><u><span><span>xmlns</span><span>:</span><span>src</span></span></u></strong><span><strong><u><span>="clr-namespace:ListDataBinding"</span></u></strong>
</span><span>Title</span><span>="BindListDataTest" </span><span>Height</span><span>="113" </span><span>Width</span><span>="300">
<</span><span>Window.Resources</span><span>>
<span> <strong><</strong></span></span><span><strong><span>src</span><span>:</span><span>People </span><span>x</span><span>:</span><span>Key</span></strong></span><span><span><strong>="Family"></strong></span>
<</span><span>src</span><span>:</span><span>Person </span><span>Name</span><span>="Jack" </span><span>Age</span><span>="18"/>
<</span><span>src</span><span>:</span><span>Person </span><span>Name</span><span>="Tom" </span><span>Age</span><span>="30"/>
<</span><span>src</span><span>:</span><span>Person </span><span>Name</span><span>="Jone" </span><span>Age</span><span>="14"/>
<</span><span>src</span><span>:</span><span>Person </span><span>Name</span><span>="Rose" </span><span>Age</span><span>="17"/>
<</span><span>src</span><span>:</span><span>Person </span><span>Name</span><span>="Mike" </span><span>Age</span><span>="13"/>
</</span><span>src</span><span>:</span><span>People</span><span>>
</</span><span>Window.Resources</span><span>>
<</span><span>Grid </span><span>DataContext</span><span>="{</span><span>StaticResource </span><span>Family</span><span>}">
<</span><span>Grid.RowDefinitions</span><span>>
<</span><span>RowDefinition</span><span>/>
<</span><span>RowDefinition</span><span>/>
</</span><span>Grid.RowDefinitions</span><span>>
<</span><span>Grid.ColumnDefinitions</span><span>>
<</span><span>ColumnDefinition </span><span>Width</span><span>="80"/>
<</span><span>ColumnDefinition </span><span>Width</span><span>="*"/>
</</span><span>Grid.ColumnDefinitions</span><span>>
<</span><span>TextBlock </span><span>Grid.Row</span><span>="0" </span><span>Grid.Column</span><span>="0" </span><span>Text</span><span>="Name" </span><span>TextAlignment</span><span>="Center" </span><span>VerticalAlignment</span><span>="Center"/>
<</span><span>TextBlock </span><span>Grid.Row</span><span>="1" </span><span>Grid.Column</span><span>="0" </span><span>Text</span><span>="Age" </span><span>TextAlignment</span><span>="Center" </span><span>VerticalAlignment</span><span>="Center"/>
<</span><span>TextBox </span><span>Grid.Row</span><span>="0" </span><span>Grid.Column</span><span>="1" </span><span>Name</span><span>="txtName" </span><strong><span><span>Text</span><span>="{</span><span>Binding </span><span>Path</span></span></strong><span><strong><span>=Name}"</span></strong> />
<</span><span>TextBox </span><span>Grid.Row</span><span>="1" </span><span>Grid.Column</span><span>="1" </span><span>Name</span><span>="txtAge" </span><span><strong><span>Text</span><span>="{</span><span>Binding </span><span>Path</span></strong></span><span><span><strong>=Age}"/</strong></span>>
</</span><span>Grid</span><span>>
</</span><span>Window</span><span>>
</span>登录后复制 |
我们发现这样的UI只能显示第一个数据项目,也就是说列表的当前项为0,至于其他的就无法显示出来了。
如果要显示其他的只有可通过如下代码的方式来取(注意:书中代码似乎有问题):
<span>private void </span>btnNext_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>People </span>people = (<span>People</span>)<span>this</span>.FindResource(<span>"Family"</span>);
txtName.Text = people[1].Name;
txtAge.Text = people[1].Age.ToString();
}登录后复制 |
取得当前项
可以通过上面的方法取得当前项,当然我们更专业的做法还是使用Collection View
还是代码说明比较简洁:
<span>People </span>people = (<span>People</span>)<span>this</span>.FindResource(<span>"Family"</span>);
<span>ICollectionView </span>view = <span>CollectionViewSource</span>.GetDefaultView(people);
<span>Person </span>peron = (<span>Person</span>)view.CurrentItem;登录后复制 |
注意:ICollectionView在System.ComponentModel命名空间里。
导航当前项
还是代码来说明更合适点:
<span> private </span><span>ICollectionView </span>GetView()
{
<span>People </span>people = (<span>People</span>)<span>this</span>.FindResource(<span>"Family"</span>);
<span>ICollectionView </span>view = <span>CollectionViewSource</span>.GetDefaultView(people);
<span>return </span>view;
}
<span>private void </span>btnNext_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>ICollectionView </span>view = GetView();
view.MoveCurrentToNext();
<span>if </span>(view.IsCurrentAfterLast)
{
view.MoveCurrentToLast();
}
}
<span>private void </span>btnPrior_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>ICollectionView </span>view = GetView();
view.MoveCurrentToPrevious();
<span>if </span>(view.IsCurrentBeforeFirst)
{
view.MoveCurrentToFirst();
}
}登录后复制 |
我们将列表数据绑定到类似TextBox这样的控件难以很好地展现列表数据。我们考虑ListBox控件来列举多个数据信息。
这时的效果如下:列表确实显示了所有对象的信息,因为我们没有设置Path属性,所以采用默认的Convertation来处理,显示对象类型。同时一定要注意使用IsSynchronizatizedWithCurrentItem=True,这样才能列表信息与其他信息同步。但究竟如何才能更好地表达我们需要的信息呢,请参看下一节:
![]()
代码示例也许更易理解:
<span><</span><span>ListBox </span><span>Grid.Row</span><span>="3" </span><span>Grid.Column</span><span>="1" </span><span>Name</span><span>="lstbox" </span><span>ItemsSource</span><span>="{</span><span>Binding</span><span>}"
</span><span>DisplayMemberPath</span><span>="Name" </span><span>SelectedValuePath</span><span>="Age" </span><span>IsSynchronizedWithCurrentItem</span><span>="True"/>
<</span><span>Button </span><span>Grid.Row</span><span>="4" </span><span>Grid.Column</span><span>="0" </span><span>Name</span><span>="btnShowValue" </span><span>Content</span><span>="ShowValue" </span><span>Click</span><span>="btnShowValue_Click" /></span>登录后复制 |
<span>private void </span>btnShowValue_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>MessageBox</span>.Show(lstbox.SelectedValue.ToString());
}登录后复制 |
这是利用ListBox控件有一个ItemTemplate属性下面,他可以接受一个DataTemplate类实例,
该模板可以重复绑定到ListBox的每一个项目元素,注意DataTemplate只能指定一个孩子节点,所以一般使用容器控件来组织下面的布局。
<span><</span><span>ListBox </span><span>Grid.Row</span><span>="3" </span><span>Grid.Column</span><span>="1" </span><span>Name</span><span>="lstbox" </span><span>ItemsSource</span><span>="{</span><span>Binding</span><span>}">
<</span><span>ListBox.ItemTemplate</span><span>>
<</span><span>DataTemplate</span><span>>
<</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>Path</span><span>=Name}">
</span><span>的年龄是</span><span><</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>Path</span><span>=Age}"></</span><span>TextBlock</span><span>>
</</span><span>TextBlock</span><span>>
</</span><span>DataTemplate</span><span>>
</</span><span>ListBox.ItemTemplate</span><span>>
</</span><span>ListBox</span><span>></span>登录后复制 <span>我本人不赞同书中这样的做法,添加一个StackPanel更舒服点。</span> 登录后复制 |
当我们改变列表的数据的时候,却出现如下现象:
![]()
只是因为我们需要绑定的列表需要实现INotifyCollectionChanged接口:
<span>namespace </span>System.Collections.Specialized
{
<span>public interface </span><span>INotifyCollectionChanged
</span>{
<span>event </span><span>NotifyCollectionChangedEventHandler </span>CollectionChanged;
}
}登录后复制 |
<span>namespace </span>System.Collections.ObjectModel
{
<span>public class </span><span>ObservableCollection</span><T> : <span>Collection</span><T>, INotifyCollectionChanged, <span>INotifyPropertyChanged
</span>{
...
}
}登录后复制 |
欢呼雀跃吧,我们改变上面例题的代码,一切如我们想象的美好。
所有的一切就如此简单,简单代码改动:
<span>//People类
</span><span>class </span><span>People </span>: <span><strong><span>ObservableCollection</span></strong></span><<span>Person</span>>
{
}登录后复制 |
![]()
简单的代码还是足以繁杂的文字,让我们看如下方法:
<span> private void </span>btnSort_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>ICollectionView </span>view = GetView();
<span>if </span>(view.SortDescriptions.Count == 0)
{
view.SortDescriptions.Add(<span>new </span><span>SortDescription</span>(<span>"Name"</span>, <span>ListSortDirection</span>.Ascending));
view.SortDescriptions.Add(<span>new </span><span>SortDescription</span>(<span>"Age"</span>, <span>ListSortDirection</span>.Descending));
}
<span>else
</span>{
view.SortDescriptions.Clear();
}
}登录后复制 |
当然我们还可以自定义排序方式:
<span> class </span><span>PersonSorter</span>:<span>IComparer
</span>{
<span>public int </span>Compare(<span>object </span>x, <span>object </span>y)
{
<span>Person </span>lhs = (<span>Person</span>)x;
<span>Person </span>rhs = (<span>Person</span>)y;
<span>// Sort Name ascending and Age descending
</span><span>int </span>nameCompare = lhs.Name.CompareTo(rhs.Name);
<span>if </span>(nameCompare != 0) <span>return </span>nameCompare;
<span>return </span>rhs.Age - lhs.Age;
}
}登录后复制 |
注意:WPF不使用System.Collection.Generic命名空间的泛型IComparer接口,而是使用System.Collection的。呵呵。
使用代码如下:
<span> private void </span>btnSort_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>ListCollectionView </span>view = (<span>ListCollectionView</span>)GetView();
<span>if </span>(view.CustomSort == <span>null</span>)
{
view.CustomSort = <span>new </span><span>PersonSorter</span>();
}
<span>else
</span>{
view.CustomSort = <span>null</span>;
}
}登录后复制 |
注意:ListCollectionView支持自定义和排序,其他的不支持。
![]()
依然是我熟悉的表达方式:代码:
<span> private void </span>btnFilter_Click(<span>object </span>sender, <span>RoutedEventArgs </span>e)
{
<span>ListCollectionView </span>view = (<span>ListCollectionView</span>)GetView();
<span>if </span>(view.Filter == <span>null</span>)
{
view.Filter = <span>delegate</span>(<span>object </span>item)
{
<span>return </span>((<span>Person</span>)item).Age > 17;
};
}
<span>else
</span>{
view.Filter = <span>null</span>;
}
}登录后复制 |
分组的意思大家很明白就是按照某一个或几个关键属性进行分类。
进行分组很简单和sort类似,只需要以下几行代码:
<span> ICollectionView </span>view = GetView();
<span>if </span>(view.GroupDescriptions.Count == 0)
{
view.GroupDescriptions.Add(<span>new </span><span>PropertyGroupDescription</span>(<span>"Age"</span>));
}
<span>else
</span>{
view.GroupDescriptions.Clear();
}登录后复制 |
但这在UI层面并没有任何影响,这需要我们对ItemsControl类的控件(例如ListBox)设置GroupStyle属性,GroupStyle类缺省地提供了一个静态的属性实现,我们可以如下设置:
<span> <</span><span>ListBox </span><span>Grid.Row</span><span>="3" </span><span>Grid.Column</span><span>="1" </span><span>Name</span><span>="lstbox" </span><span>ItemsSource</span><span>="{</span><span>Binding</span><span>}" </span><span>IsSynchronizedWithCurrentItem</span><span>="True">
<strong><span><</span></strong></span><span><strong><span>ListBox.GroupStyle</span></strong></span><strong><span><span>>
<</span><span>x</span><span>:</span><span>Static </span><span>Member</span></span><span><span>="GroupStyle.Default"/>
</</span><span>ListBox.GroupStyle</span></span></strong><span><strong><span>></span></strong>
<</span><span>ListBox.ItemTemplate</span><span>>
<</span><span>DataTemplate</span><span>>
<</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>Path</span><span>=Name}">
</span><span>的年龄是</span><span><</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>Path</span><span>=Age}"></</span><span>TextBlock</span><span>>
</</span><span>TextBlock</span><span>>
</</span><span>DataTemplate</span><span>>
</</span><span>ListBox.ItemTemplate</span><span>>
</</span><span>ListBox</span><span>></span>登录后复制 |
但也许这并不是我们所喜欢的界面,简单得让人生厌,还好微软提供了这个对象的一个属性:HeaderTemplate用于定义分组的栏目的外观,微软总是为大家想得那么周到,养活那么多天才是需要钱的,希望大家不要老是讲微软的坏话。
<span> <</span><span>ListBox.GroupStyle</span><span>>
<</span><span>GroupStyle</span><span>>
<</span><span>GroupStyle.HeaderTemplate</span><span>>
<</span><span>DataTemplate</span><span>>
<</span><span>StackPanel </span><span>Background</span><span>="Green" </span><span>Orientation</span><span>="Horizontal">
<</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>Name</span><span>}"/>
<</span><span>TextBlock </span><span>Text</span><span>="("/>
<</span><span>TextBlock </span><span>Text</span><span>="{</span><span>Binding </span><span>ItemCount</span><span>}"/>
<</span><span>TextBlock </span><span>Text</span><span>=")"/>
</</span><span>StackPanel</span><span>>
</</span><span>DataTemplate</span><span>>
</</span><span>GroupStyle.HeaderTemplate</span><span>>
</</span><span>GroupStyle</span><span>>
</</span><span>ListBox.GroupStyle</span><span>></span>登录后复制 |
有这模板属性一切由你发挥,真是好也,然而即使这样解决了UI问题,但是如果我们还希望更进一步,能否实现范围内分组呢?呵呵,然也:
这时我们不需要去想着如何继承GroupStyle类,而是采用围魏救赵的方式,定义一个IValueConverter,
<span> public class </span><span>AgeRangeConvert </span>: <span>IValueConverter
</span>{
<span>public object </span>Convert(<span>object </span>value, <span>Type </span>targetType, <span>object </span>parameter, <span>CultureInfo </span>culture)
{
<span>int </span>_value = (<span>int</span>)value;
<span>if </span>(_value <= 10)
<span>return </span><span>"10岁以下"</span>;
<span>else if </span>(_value <= 20)
<span>return </span><span>"20岁以下"</span>;
<span>else
return </span><span>"20岁以上"</span>;
}
<span>public object </span>ConvertBack(<span>object </span>value, <span>Type </span>targetType, <span>object </span>parameter, <span>CultureInfo </span>culture)
{
<span>throw new </span><span>NotImplementedException</span>();
}
}登录后复制 |
简单调整前面分组代码:
<span> ICollectionView </span>view = GetView();
<span>if </span>(view.GroupDescriptions.Count == 0)
{
view.GroupDescriptions.Add(<span>new </span><span>PropertyGroupDescription</span>(<span>"Age"</span>,<span>new </span><span>AgeRangeConvert</span>()));
}
<span>else
</span>{
view.GroupDescriptions.Clear();
}登录后复制 |
一切搞定,享受成果吧:
![]()
既然GroupDescripions是个集合类型,我们不妨看下面代码究竟是什么效果:
<span> ICollectionView </span>view = GetView();
<span>if </span>(view.GroupDescriptions.Count == 0)
{
view.GroupDescriptions.Add(<span>new </span><span>PropertyGroupDescription</span>(<span>"Age"</span>,<span>new </span><span>AgeRangeConvert</span>()));
view.GroupDescriptions.Add(<span>new </span><span>PropertyGroupDescription</span>(<span>"Age"</span>));
}
<span>else
</span>{
view.GroupDescriptions.Clear();
}登录后复制 |
运行如下:
![]()
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