siliverlight Combox

找不到控件我只是加了个IsSelected="True" 这是怎么回事
.xaml 页面代码

<navigation:Page x:Class="SilverlightTest.Real" 

           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"

           mc:Ignorable="d"

           xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"

           d:DesignWidth="640" d:DesignHeight="480"

           Title="Real Page">

    <Grid x:Name="LayoutRoot" Background="White">

        <Grid.RowDefinitions>

            <RowDefinition Height="Auto"></RowDefinition>

            <RowDefinition Height="Auto"></RowDefinition>

            <RowDefinition Height="Auto"></RowDefinition>

        </Grid.RowDefinitions>

        <TextBlock Text="选择控件" Margin="5,10,10,10"  FontSize="18" FontWeight="Bold" Foreground="#FFBE4D4D" Grid.Row="0"></TextBlock>

        <Grid Grid.Row="1" Margin="5,0,0,5">

            <Grid.RowDefinitions>

                <RowDefinition Height="Auto"></RowDefinition>

                <RowDefinition Height="Auto"></RowDefinition>

                <RowDefinition Height="Auto"></RowDefinition>

                <RowDefinition Height="Auto"></RowDefinition>

                <RowDefinition Height="Auto"></RowDefinition>

                <RowDefinition Height="Auto"></RowDefinition>

            </Grid.RowDefinitions>

            <Grid.ColumnDefinitions>

                <ColumnDefinition Width="Auto"></ColumnDefinition>

                <ColumnDefinition Width="Auto"></ColumnDefinition>

                <ColumnDefinition Width="Auto"></ColumnDefinition>

                <ColumnDefinition Width="Auto"></ColumnDefinition>

            </Grid.ColumnDefinitions>

            <TextBlock Text="字体：" Grid.Row="0" Grid.Column="0"></TextBlock>

            <ComboBox Name="fontComboBox" Width="150" ItemsSource="{Binding}" Grid.Row="0" Grid.Column="1" SelectionChanged="fontComboBox_SelectionChanged"></ComboBox>

            <TextBlock Text="大小：" Grid.Row="0" Grid.Column="2"></TextBlock>

            <ComboBox Name="fontSizeComboBox" Width="80" Grid.Row="0" Grid.Column="3" SelectionChanged="fontSizeComboBox_SelectionChanged">

                <ComboBoxItem Content="12"  IsSelected="True"></ComboBoxItem>

                <ComboBoxItem Content="13"></ComboBoxItem>

                <ComboBoxItem Content="14"></ComboBoxItem>

                <ComboBoxItem Content="15"></ComboBoxItem>

                <ComboBoxItem Content="16"></ComboBoxItem>

            </ComboBox>

            <TextBlock Name="textBlock1"  Text="测试内容" Margin="10,5,0,0" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="4">

            </TextBlock>

            <TextBlock Name="textBlock2" Text="测试内容2" Grid.Row="2" Grid.Column="0" Grid.ColumnSpan="4" Margin="10,5,0,0"></TextBlock>

            <TextBlock Name="textBlock3" Text="测试内容3" Grid.Row="3" Grid.Column="0" Grid.ColumnSpan="4" Margin="10,5,0,0"></TextBlock>

            <TextBlock Name="textBlock4" Text="测试内容4" Margin="10,5,0,0" Grid.Row="4" Grid.Column="0" Grid.ColumnSpan="4">

            </TextBlock>

            <TextBlock Name="textBlock5" Text="测试内容5" Margin="10,5,0,0" Grid.Row="5" Grid.Column="0" Grid.ColumnSpan="4">

            </TextBlock>

        </Grid>

    </Grid>

</navigation:Page>

后台。cs 文件

using System;

using System.Collections.Generic;

using System.Linq;

using System.Net;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Animation;

using System.Windows.Shapes;

using System.Windows.Navigation;

using System.Collections.ObjectModel;//ObservableCollection



namespace SilverlightTest

{

    public partial class Real : Page

    {

        public Real()

        {

            InitializeComponent();

            ObservableCollection<FontFamily> fonts = new ObservableCollection<FontFamily>();

            fonts.Add(new FontFamily("Cambria"));

            fonts.Add(new FontFamily("Arial Unicode MS"));

            fonts.Add(new FontFamily("Batang"));

            fonts.Add(new FontFamily("Dotum"));

            this.fontComboBox.DataContext = fonts;//这样完成了绑定；

            this.fontComboBox.SelectedItem = new FontFamily("Cambria");//默认值

        }



        // 当用户导航到此页面时执行。

        protected override void OnNavigatedTo(NavigationEventArgs e)

        {

        }



        private void fontComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)

        {

            ComboBox cb = sender as ComboBox;

            this.textBlock1.FontFamily = (FontFamily)cb.SelectedItem;

            this.textBlock2.FontFamily = (FontFamily)cb.SelectedItem;

            this.textBlock3.FontFamily = (FontFamily)cb.SelectedItem;

            this.textBlock4.FontFamily = (FontFamily)cb.SelectedItem;

            this.textBlock5.FontFamily = (FontFamily)cb.SelectedItem;



        }



        private void fontSizeComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)

        {

            

               ComboBox cb = sender as ComboBox;

                int fontSize = int.Parse(((ComboBoxItem)cb.SelectedItem).Content.ToString());

                this.textBlock1.FontSize =  double.Parse(fontSize.ToString());

                this.textBlock2.FontSize = fontSize+1;

                this.textBlock3.FontSize = fontSize+2;

                this.textBlock4.FontSize = fontSize+3;

                this.textBlock5.FontSize = fontSize + 4;

           



        }



    }

}

运行后在
fontSizeComboBox_SelectionChanged 这个地方报未将对象引用到对象的实例
siliverlight C# Combox --------------------编程问答--------------------

private void fontSizeComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)

        {

             

               ComboBox cb = sender as ComboBox;

                int fontSize = int.Parse(((ComboBoxItem)cb.SelectedItem).Content.ToString());

                if(cb.SelectedItem!=null)

                { 

                   //再设置字体?

                 }

            

 

        }

--------------------编程问答-------------------- 谢了你啦搞不明白为啥会执行这个方法啊只是开始加载

补充：.NET技术 ,  ASP.NET