先回忆一下aspx中的处理:
在aspx中，可以直接在后台定义一个变量，然后前台就可以用<%=xxx%>来将其"绑定"html控件上，比如下面这样，实在是很方便:
代码语言：js复制using System;
namespace WebApplication1
{
public partial class _Default : System.Web.UI.Page
{
protected string _Test = DateTime.Now.ToString();
protected void Page_Load(object sender, EventArgs e)
{
}
}
}代码
代码语言：js复制<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication1._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<input id="Text1" type="text" value="<%=_Test %>"/>
</form>
</body>
</html>但到了Silverlight中，要想直接将后台的变量绑定到某个控件上却是行不通的，通常我们得先定义一个类，然后在类里定义属性，才能把类实例的属性绑定到控件:
简单绑定:
代码
代码语言：js复制using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Shapes;
namespace BindVariable
{
public partial class MainPage : UserControl
{
public class MyClass { public string Test { set; get; } }
public MyClass TestClass;
public MainPage()
{
InitializeComponent();
TestClass = new MyClass();
TestClass.Test = "123";
this.textBox1.DataContext = TestClass;
}
}
}
<StackPanel>
<TextBox x:Name="textBox1" Text="{Binding Test}"/>
</StackPanel>这样就完成了功能最简单的绑定，还想玩得更深入一点，比如实现OneWay,TwoWay方式的绑定(不清楚绑定模式的朋友，建议先参看https://cloud.tencent.com/developer/article/1027125)，这样仍然不行，比如我们稍微把刚才的代码改一下:
"自动更新"的绑定:
代码
代码语言：js复制<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
x:Class="BindVariable.MainPage"
>
<StackPanel Orientation="Vertical">
<TextBox x:Name="textBox1" Text="{Binding Test}"/>
<Button x:Name="btnChange" Content="Change Test" Click="btnChange_Click"></Button>
</StackPanel>
</UserControl>代码
代码语言：js复制using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Shapes;
namespace BindVariable
{
public partial class MainPage : UserControl
{
public class MyClass { public string Test { set; get; } }
public MyClass TestClass;
public MainPage()
{
InitializeComponent();
TestClass = new MyClass();
TestClass.Test = "123";
this.textBox1.DataContext = TestClass;
}
private void btnChange_Click(object sender, RoutedEventArgs e)
{
this.TestClass.Test = "456";
}
}
}运行后，点击按钮，发现textbox1中的内容并无变化，原因是：要想实现源与目标的数据自动关联更新，MyClass得实现INotifyPropertyChanged接口，我们把MyClass的定义改成下面这样:
代码
代码语言：js复制public class MyClass:INotifyPropertyChanged {
public event PropertyChangedEventHandler PropertyChanged;
private string _test;
public string Test
{
set{
_test = value;
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("Test"));
}
}
get { return _test; }
}
}再次运行，发现点击按钮后，textbox1的内容变成了456，达到预期的效果了. 绑定集合(数据集):
很多应用场合中，数据来源不仅只有一个实例(或一条记录)--比如从数据库中检索的记录，这时如果想绑定数据并实现自动更新，应使用集合绑定(类似于aspx中的DataSet或DataTable)。要注意的是，使用集合绑定并实现自动更新，除了要实现 INotifyPropertyChanged 外，还要实现 INotifyCollectionChanged。幸好.net框架已经有一个ObservableCollection<T> 类，该类具有 INotifyCollectionChanged 和 INotifyPropertyChanged 的内置实现。可以直接拿来用:
代码
代码语言：js复制<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
x:Class="BindVariable.MainPage"
xmlns:local="clr-namespace:BindVariable"
>
<StackPanel Orientation="Vertical">
<ListBox x:Name="lst" >
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding Test}"></TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button x:Name="btnChange" Content="Change Test" Click="btnChange_Click"></Button>
</StackPanel>
</UserControl>代码
代码语言：js复制using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
namespace BindVariable
{
public partial class MainPage : UserControl
{
public class MyClass { public string Test { set; get; } }
ObservableCollection<MyClass> oc = new ObservableCollection<MyClass>(){
new MyClass() { Test = "1" },
new MyClass() { Test = "2" },
new MyClass() { Test = "3" }
};
public MainPage()
{
InitializeComponent();
this.lst.ItemsSource = oc;
}
private void btnChange_Click(object sender, RoutedEventArgs e)
{
oc.Add(new MyClass() { Test = "4" });
}
}
}IValueConverter:
上述的绑定，都是将数据原封不动的绑定并显示，如果我们希望在绑定时，能对数据的输出做一些变化，比如：代表性别的"1,0"输出时希望变成"男,女"，该怎么办呢？(silverlight中可不允许象aspx那样用<%# Eval("Sex").ToString()=="1"?"男":"女"%>来搞定) 答案:IValueConverter
代码
代码语言：js复制using System;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
namespace BindVariable
{
public partial class MainPage : UserControl
{
public class MyClass
{
public string Test { set; get; }
public bool Sex { set; get; }
}
ObservableCollection<MyClass> oc = new ObservableCollection<MyClass>(){
new MyClass() { Test = "1",Sex=true },
new MyClass() { Test = "2",Sex=false },
new MyClass() { Test = "3",Sex=true }
};
public MainPage()
{
InitializeComponent();
this.lst.ItemsSource = oc;
}
private void btnChange_Click(object sender, RoutedEventArgs e)
{
oc.Add(new MyClass() { Test = "4", Sex = false });
}
}
/// <summary>
/// bool转化为性别字符串
/// </summary>
public class BoolToSexConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
try
{
return ((bool)value) ? "男" : "女";
}
catch
{
return "?";
}
}
//只有TwoWay模式下，才需要实现该方法，否则可以不用理
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
}<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
x:Class="BindVariable.MainPage"
xmlns:local="clr-namespace:BindVariable"
>
<StackPanel Orientation="Vertical">
<StackPanel.Resources>
<local:BoolToSexConverter x:Key="Bool2Sex"></local:BoolToSexConverter>
</StackPanel.Resources>
<ListBox x:Name="lst" >
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Test}"></TextBlock>
<TextBlock Text="，"></TextBlock>
<TextBlock Text="{Binding Path=Sex, Converter={StaticResource Bool2Sex}}"></TextBlock>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button x:Name="btnChange" Content="Change Test" Click="btnChange_Click"></Button>
</StackPanel>
</UserControl>也许您注意到了IValueConverter的Convert方法中，还能传入参数！我们可以利用这个玩点小花样，比如界面上有三个矩形，其中"矩形2的宽度"等于"矩形1的宽度" "一个任意指定的固定值"，矩形3的宽度矩形1与矩形2的宽度总和，不允用 rect2.width = rect1.width，rect3.width = rect2.width rect1.width 来处理:) 您会怎么做呢？
代码
代码语言：js复制using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
namespace BindVariable
{
public partial class MainPage : UserControl
{
public MainPage()
{
InitializeComponent();
}
}
public class DoubleAddConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
try
{
return double.Parse(value.ToString()) double.Parse(parameter.ToString());
}
catch
{
return 50.0;
}
}
//只有TwoWay模式下，才需要实现该方法，否则可以不用理
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
public class FrameworkElementAddConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
try
{
return double.Parse(value.ToString()) ((App.Current.RootVisual as FrameworkElement).FindName(parameter.ToString()) as FrameworkElement).Width;
}
catch
{
return 50.0;
}
}
//只有TwoWay模式下，才需要实现该方法，否则可以不用理
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
}<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
x:Class="BindVariable.MainPage"
xmlns:local="clr-namespace:BindVariable"
>
<StackPanel Orientation="Vertical" HorizontalAlignment="Left" >
<StackPanel.Resources>
<local:DoubleAddConverter x:Key="DoubleAdd"></local:DoubleAddConverter>
<local:FrameworkElementAddConverter x:Key="FEAdd"></local:FrameworkElementAddConverter>
</StackPanel.Resources>
<Rectangle x:Name="rect1" Width="100" Height="50" Fill="Gray" HorizontalAlignment="Left"></Rectangle>
<Rectangle x:Name="rect2" Height="50" Width="{Binding Width, Converter={StaticResource DoubleAdd}, ConverterParameter=100, ElementName=rect1, Mode=OneWay}" Fill="Red" HorizontalAlignment="Left"></Rectangle>
<Rectangle x:Name="rect3" Height="50" Fill="Blue" Width="{Binding Width, Converter={StaticResource FEAdd}, ConverterParameter=rect2, ElementName=rect1, Mode=OneWay}"></Rectangle>
</StackPanel>
</UserControl>这样就搞定了，也许有人会问：为啥不用 rect2.width = rect1.width，rect3.width = rect2.width rect1.width 呢?不是更简单吗？
存在即合理，这样的好处是不必用硬编码把逻辑写死，我们可以把常用的转换处理抽象出来，比如封装成一个单纯的dll程序集，以后需要用到的地方，直接引用就可以了，能有效的重用代码。
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