SilverLight的Slider控件的学习遇到的问题

时间：2011-05-27 来源：紫电雷龙

Slider控件有两个设定最大（Maximum）最小（Minimum）范围的属性，默认分别为1,0.当人为设定这两个值并在ValueChanged事件中引用了该控件就会报NoneReferenceException的错误，原因是Slider控件没有被实例化，因为我们人为的设置了最大最小属性，在过初始化方法（InitializeComponent）时触发了ValueChanged事件，这个时候Slider还没有加载完就引用了它的实例，报了错。

报错代码如下：

XAML：


<UserControl x:Class="SliderBarTest.MainPage"
    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"
    d:DesignHeight="300" d:DesignWidth="400">

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="50"/>
            <RowDefinition Height="30"/>
            <RowDefinition Height="20"/>
            <RowDefinition Height="180"/>
            <RowDefinition Height="20"/>
            
        </Grid.RowDefinitions>
        <TextBlock Text="选择控件-Silder" FontSize="24" FontWeight="Bold" FontFamily="Comic Sans MS" Grid.Row="0"/>
        <Slider x:Name="silder1" Minimum="0" Maximum="10" Grid.Row="1" Margin="10,0,10,0" ValueChanged="silder1_ValueChanged"/>
        <TextBlock FontSize="15" FontFamily="Comic Sans MS" Text="silder1" Grid.Row="2" Margin="10,0,10,0" x:Name="textSlider1"/>
        <Slider x:Name="slider2" Minimum="1" Maximum="10" Orientation="Vertical" Grid.Row="3" Margin="10,10,370,10" ValueChanged="slider2_ValueChanged" />
        <TextBlock Text="slider2" FontSize="15" FontFamily="Comic Sans MS" Grid.Row="4" Margin="10,0,10,0" x:Name="textSlider2"/>
    </Grid>
</UserControl>

 C#: 1 using System;
 2  using System.Collections.Generic;
 3  using System.Linq;
 4  using System.Net;
 5  using System.Windows;
 6 using System.Windows.Controls;
 7 using System.Windows.Documents;
 8 using System.Windows.Input;
 9 using System.Windows.Media;
10 using System.Windows.Media.Animation;
11 using System.Windows.Shapes;
12 
13 namespace SliderBarTest
14 {
15     public partial class MainPage : UserControl
16     {
17         public MainPage()
18         {
19             InitializeComponent();
20             //silder1.ValueChanged+=new RoutedPropertyChangedEventHandler<double>(silder1_ValueChanged);
21             //slider2.ValueChanged+=new RoutedPropertyChangedEventHandler<double>(slider2_ValueChanged);
22         }
23 
24         private void silder1_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
25         {
26             textSlider1.Text = "水平滑块的当前值为："+silder1.Value ;
27         }
28 
29         private void slider2_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
30         {
31             textSlider2.Text = "垂直滑块的当前值为：" + slider2.Value;
32         }
33 
34 
35     }
36 }

解决办法是把XAML文件中灰色部分去掉，c#文件中灰色注释部分打开。