Silverlight】解决DataTemplate绑定附加属性
本文 Silverlight 版本：4.0。
首先定义数据类型，此文始终使用此定义类型。
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public class SimpleData : ViewModelBase |
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{ |
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private string _text; |
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private int _column, _row; |
5 |
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public string Text { get { return _text; } set { _text = value; OnPropertyChanged("Text"); } } |
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public int Column { get { return _column; } set { _column = value; OnPropertyChanged("Column"); } } |
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public int Row { get { return _row; } set { _row = value; OnPropertyChanged("Row"); } } |
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} |
前台代码：
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<Grid x:Name="LayoutRoot" Background="White"> |
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<ItemsControl ItemsSource="{Binding}"> |
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<ItemsControl.ItemTemplate> |
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<DataTemplate> |
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<TextBox Text="{Binding Text}" |
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Foreground="Green" |
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Grid.Row="{Binding Row}" |
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Grid.Column="{Binding Column}" |
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Height="30" Width="150" |
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/> |
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</DataTemplate> |
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</ItemsControl.ItemTemplate> |
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<ItemsControl.ItemsPanel> |
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<ItemsPanelTemplate> |
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<Grid ShowGridLines="True"> |
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<Grid.RowDefinitions> |
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<RowDefinition/> |
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<RowDefinition/> |
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<RowDefinition/> |
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</Grid.RowDefinitions> |
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<Grid.ColumnDefinitions> |
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<ColumnDefinition/> |
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<ColumnDefinition/> |
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</Grid.ColumnDefinitions> |
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</Grid> |
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</ItemsPanelTemplate> |
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</ItemsControl.ItemsPanel> |
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</ItemsControl> |
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</Grid> |
后台代码：
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public partial class MainPage : UserControl |
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{ |
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public MainPage() |
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{ |
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InitializeComponent(); |
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this.DataContext = new SimpleData[] |
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{ |
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new SimpleData{ Text = "111111", Column = 0, Row = 0 }, |
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new SimpleData{ Text = "222222", Column = 1, Row = 1 }, |
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new SimpleData{ Text = "333333", Column = 0, Row = 2 }, |
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}; |
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} |
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} |
可以看出这段代码的本意是通过绑定的方式设置，在 ItemsControl 里面显示 3 个 TextBox，同时指定了相应在 Grid 的行和列。
但是，你懂的！
这样的代码肯定是不能正确运行。特别是在Silverlight。
如果这是在 WPF 环境，很庆幸你还可以用 ItemContainerStyle 搞定：
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<ItemsControl.ItemContainerStyle> |
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<Style> |
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<Setter Property="Grid.Row" Value="{Binding Row, Mode=OneWay}"/> |
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<Setter Property="Grid.Column" Value="{Binding Column, Mode=OneWay}"/> |
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</Style> |
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</ItemsControl.ItemContainerStyle> |
只可惜这是在 Silverlight 环境。我们只能够想别的办法了。
为什么不可以？拿出 Silverlight Spy 或者 Snoop 查看相应的 VisualTree。可以看到在 TextBox 外面还套了一个 ContextPresenter。
于是我们可以想到，能不能设置 ContextPresenter 的 Grid.Row 和 Grid.Colume 达到控制行列的目的？
于是我们得到下面的思路，使用附加属性把相应的绑定关系提升。
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using System; |
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using System.Collections.Generic; |
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using System.Globalization; |
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using System.Linq; |
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using System.Reflection; |
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using System.Windows; |
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using System.Windows.Controls; |
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using System.Windows.Data; |
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using System.Windows.Media; |
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|
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namespace Delay |
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{ |
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public class UpUp : DependencyObject |
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{ |
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// Using a DependencyProperty as the backing store for Up. This enables animation, styling, binding, etc... |
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public static readonly DependencyProperty UpProperty = |
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DependencyProperty.RegisterAttached("Up", typeof(string), typeof(UpUp), new PropertyMetadata(string.Empty)); |
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|
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public static void SetUp(FrameworkElement element, string value) |
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{ |
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HanderClosure hander = element.GetValue(UpProperty) as HanderClosure; |
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if (hander == null) |
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{ |
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hander = new HanderClosure(element, value); |
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element.SetValue(UpProperty, value); |
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element.LayoutUpdated += new EventHandler(hander.element_LayoutUpdated); |
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} |
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} |
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public static string GetUp(FrameworkElement element) |
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{ |
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HanderClosure hander = element.GetValue(UpProperty) as HanderClosure; |
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if (hander == null) |
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return null; |
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else |
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return hander.OrgParamenter; |
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} |
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|
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private class HanderClosure |
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{ |
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private FrameworkElement _elem = null; |
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private string[] propertys = null; |
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private int _level; |
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private UpMode _mode; |
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private string _orgParamenter; |
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|
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public string OrgParamenter { get { return _orgParamenter; } } |
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|
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public HanderClosure(FrameworkElement element, string parameter) |
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{ |
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if (element == null) |
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throw new ArgumentNullException("element"); |
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if (parameter == null) |
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throw new ArgumentNullException("parameter"); |
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_elem = element; |
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_level = 1; |
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_mode = UpMode.Copy; |
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_orgParamenter = parameter; |
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|
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string[] array = parameter.Split(new char[] { ';' }, StringSplitOptions.RemoveEmptyEntries); |
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if (array.Length == 0) |
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throw new ArgumentException("parameter"); |
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propertys = array[0].Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries); |
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if (array.Length > 1) |
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{ |
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int num; |
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if (int.TryParse(array[1].Trim(), out num)) |
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{ |
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_level = num; |
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} |
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} |
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if (array.Length > 2) |
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{ |
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UpMode mode; |
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if (Enum.TryParse<UpMode>(array[2].Trim(), true, out mode)) |
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{ |
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_mode = mode; |
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} |
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} |
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} |
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|
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public void element_LayoutUpdated(object sender, EventArgs e) |
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{ |
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FrameworkElement parent = _elem; |
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for (int i = 0; i < _level && parent != null; i++) |
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{ |
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parent = VisualTreeHelper.GetParent(parent) as FrameworkElement; |
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} |
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if (parent == null) |
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return; |
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|
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foreach (string property in propertys) |
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{ |
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Apply(_elem, parent, property.Trim()); |
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} |
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} |
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|
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// Copyright (C) Microsoft Corporation. All Rights Reserved. |
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// This code released under the terms of the Microsoft Public License |
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// (Ms-PL, http://opensource.org/licenses/ms-pl.html). |
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private void Apply(FrameworkElement element1, FrameworkElement element2, string property) |
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{ |
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var array = property.Split('.'); |
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if (array.Length != 2) |
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throw new ArgumentException("property"); |
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string typeName = array[0].Trim(); |
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string propertyName = array[1].Trim(); |
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|
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Type type = null; |
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foreach (var assembly in AssembliesToSearch) |
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{ |
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// Match on short or full name |
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type = assembly.GetTypes() |
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.Where(t => (t.FullName == typeName) || (t.Name == typeName)) |
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.FirstOrDefault(); |
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if (type != null) |
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break; |
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} |
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if (null == type) |
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{ |
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// Unable to find the requested type anywhere |
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throw new ArgumentException( |
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string.Format( |
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CultureInfo.CurrentCulture, |
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"Unable to access type \"{0}\". Try using an assembly qualified type name.", |
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typeName)); |
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} |
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|
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// Get the DependencyProperty for which to set the Binding |
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DependencyProperty dp = null; |
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var field = type.GetField( |
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propertyName + "Property", |
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BindingFlags.FlattenHierarchy | BindingFlags.Public | BindingFlags.Static); |
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if (null != field) |
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{ |
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dp = field.GetValue(null) as DependencyProperty; |
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} |
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if (null == dp) |
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{ |
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// Unable to find the requsted property |
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throw new ArgumentException( |
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string.Format( |
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CultureInfo.CurrentCulture, |
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"Unable to access DependencyProperty \"{0}\" on type \"{1}\".", |
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propertyName, |
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type.Name)); |
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} |
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|
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BindingExpression binding = element1.GetBindingExpression(dp); |
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object value = element1.GetValue(dp); |
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if (binding != null) |
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{ |
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element2.SetBinding(dp, binding.ParentBinding); |
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} |
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else if (value != null) |
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{ |
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element2.SetValue(dp, value); |
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} |
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if (_mode == UpMode.Move) |
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element1.ClearValue(dp); |
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} |
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|
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// Copyright (C) Microsoft Corporation. All Rights Reserved. |
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// This code released under the terms of the Microsoft Public License |
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// (Ms-PL, http://opensource.org/licenses/ms-pl.html). |
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/// <summary> |
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/// Gets a sequence of assemblies to search for the provided type name. |
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/// </summary> |
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private IEnumerable<Assembly> AssembliesToSearch |
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{ |
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get |
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{ |
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// Start with the System.Windows assembly (home of all core controls) |
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yield return typeof(Control).Assembly; |
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|
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#if SILVERLIGHT && !WINDOWS_PHONE |
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// Fall back by trying each of the assemblies in the Deployment's Parts list |
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foreach (var part in Deployment.Current.Parts) |
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{ |
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var streamResourceInfo = Application.GetResourceStream( |
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new Uri(part.Source, UriKind.Relative)); |
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using (var stream = streamResourceInfo.Stream) |
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{ |
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yield return part.Load(stream); |
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} |
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} |
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#endif |
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} |
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} |
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} |
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|
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private enum UpMode |
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{ |
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Move, |
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Copy, |
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} |
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} |
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} |
如何使用？使用非常简单！
在你的项目中增加 UpUp 之后，在需要提升绑定级别的 Page 的 Xaml 中引入命名空间 xmlns:delay="clr-namespace:Delay"。然后在需要提升绑定级别的控件中加入属性 delay:UpUp.Up="Grid.Row,Grid.Column"。得到完整的前台代码如下：
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<UserControl x:Class="TestValueBindingInItemTemplate.MainPage" |
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xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" |
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xmlns:d="http://schemas.microsoft.com/expression/blend/2008" |
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xmlns:delay="clr-namespace:Delay" |
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mc:Ignorable="d" |
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d:DesignHeight="300" d:DesignWidth="400"> |
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|
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<Grid x:Name="LayoutRoot" Background="White"> |
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<ItemsControl ItemsSource="{Binding}"> |
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<ItemsControl.ItemTemplate> |
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<DataTemplate> |
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<TextBox Text="{Binding Text}" |
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Foreground="Green" |
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Grid.Row="{Binding Row}" |
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Grid.Column="{Binding Column}" |
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Height="30" Width="150" |
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delay:UpUp.Up="Grid.Row,Grid.Column" |
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/> |
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</DataTemplate> |
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</ItemsControl.ItemTemplate> |
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<ItemsControl.ItemsPanel> |
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<ItemsPanelTemplate> |
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<Grid ShowGridLines="True"> |
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<Grid.RowDefinitions> |
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<RowDefinition/> |
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<RowDefinition/> |
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<RowDefinition/> |
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</Grid.RowDefinitions> |
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<Grid.ColumnDefinitions> |
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<ColumnDefinition/> |
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<ColumnDefinition/> |
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</Grid.ColumnDefinitions> |
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</Grid> |
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</ItemsPanelTemplate> |
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</ItemsControl.ItemsPanel> |
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</ItemsControl> |
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</Grid> |
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</UserControl> |
UpUp.Up 应该如何填写？实际上 UpUp.Up 属性有具体的语法格式：
UpUp.Up="Type.Property[,Type.Property ...][;Level[;Move|Copy]]"
其中
Type.Property 是需要提升绑定关系的属性名称，可以用逗号把多个属性名称隔开。
Level 是整数，表示需要提升的层次。在 VisualTree 中向上一层为一个层次。
Move|Copy 是枚举类型，表示提升之后保留原来的绑定关系。
例如：delay:UpUp.Up="Grid.Row,Grid.Column;1;Copy"
有了 UpUp 之后，对于类似的绑定问题可以轻而易举的完成了！
PS：WPF 也可以用此方法实现，但是有细节方面的差异。
1、不能够使用SetXXX GetXXX，要使用 XXX 属性。
2、需要注册 PropertyChangedCallback 事件，并将相关注册 Hander 部分放置到此方法内。
