动态创建控件出错.

Question

TextBlock textblock = new TextBlock();
textblock.Text = comboItem.Content.ToString();

DisplayStackPanel.Children.Add(textblock);//这一步提示,未将对象引用到实例


Xaml中
<StackPanel Grid.Row="5" Grid.Column="0" x:Name="DisplayStackPanel"></StackPanel>

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Answer 1

我是在这个事件中写的代码.
private void ColumnComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            ComboBox combo = sender as ComboBox;
            ComboBoxItem comboItem = (ComboBoxItem)combo.SelectedItem;

            //GridLength height = new GridLength(50);
            //GridLength width = new GridLength(200);

            RowDefinition rowdef = new RowDefinition();
            //rowdef.Height = height;
            DisplayStyleGrid.RowDefinitions.Add(rowdef);

            ColumnDefinition coldef = new ColumnDefinition();
            //coldef.Width = width;
            DisplayStyleGrid.ColumnDefinitions.Add(coldef);

            TextBox tb = new TextBox();
            tb.Width = 110;
            tb.Height = 30;
            tb.Text = "aa";

            DisplayStyleGrid.Children.Add(tb);
            DisplayStyleGrid.SetValue(Grid.ShowGridLinesProperty, true);
            tb.SetValue(Grid.ColumnProperty, 0);
            tb.SetValue(Grid.RowProperty, 0);
        }

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Answer 2

<UserControl x:Class="SilverlightApplication10.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="400" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="100"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <StackPanel Grid.Row="0" Grid.Column="0" x:Name="DisplayStackPanel"></StackPanel>
        <ComboBox x:Name="cmbSelect" Grid.Row="0" Grid.Column="1" SelectionChanged="cmbSelect_SelectionChanged">
            <ComboBox.Items>
                <ComboBoxItem Content="1"></ComboBoxItem>
                <ComboBoxItem Content="2"></ComboBoxItem>
            </ComboBox.Items>
        </ComboBox>
        <Grid  x:Name="DisplayStyleGrid">
            
        </Grid>
    </Grid>
</UserControl>

我按你提供的信息，我做了一个，没有出现你说的情况啊！我想是不是我在那里理解上有误吧！

TextBlock textblock = new TextBlock();
textblock.Text = comboItem.Content.ToString();

DisplayStackPanel.Children.Add(textblock);//这一步提示,未将对象引用到实例
你这个是在那个方法里调用？我把这个加到cmbSelect_SelectionChanged 事件中试过，也没有出错！

后台代码：

namespace SilverlightApplication10
{
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();
        }

        private void cmbSelect_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            ComboBox combo = sender as ComboBox;
            ComboBoxItem comboItem = (ComboBoxItem)combo.SelectedItem;

            //GridLength height = new GridLength(50);
            //GridLength width = new GridLength(200);

            RowDefinition rowdef = new RowDefinition();
            //rowdef.Height = height;
            DisplayStyleGrid.RowDefinitions.Add(rowdef);

            ColumnDefinition coldef = new ColumnDefinition();
            //coldef.Width = width;
            DisplayStyleGrid.ColumnDefinitions.Add(coldef);


            //TextBox tb = new TextBox();
            //tb.Width = 110;
            //tb.Height = 30;
            //tb.Text = "aa";



            //DisplayStyleGrid.Children.Add(tb);


            TextBlock tb = new TextBlock();
            tb.Text = comboItem.Content.ToString();

            DisplayStackPanel.Children.Add(tb);//这一步提示,未将对象引用到实例


            DisplayStyleGrid.SetValue(Grid.ShowGridLinesProperty, true);
            tb.SetValue(Grid.ColumnProperty, 0);
            tb.SetValue(Grid.RowProperty, 0);


        }
    }
}

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努力！写一个js解析器,一个svg插件,一个绘图程序,做好自己,呵呵～！

Answer 3

TextBlock textblock = new TextBlock();
textblock.Text = comboItem.Content.ToString();

DisplayStackPanel.Children.Add(textblock);//这一步提示,未将对象引用到实例


Xaml中
<StackPanel Grid.Row="5" Grid.Column="0" x:Name="DisplayStackPanel"></StackPanel>

---

aaaa

其他对象出错的吧,比如你textblock声明在一个方法内,而DisplayStackPanel.Children.Add(textblock);再另一个方法内

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Answer 4

private void ColumnComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)

这个是事件,在刚调用childwindow时,就执行了一次,DisplayStyleGrid.RowDefinitions.Add(rowdef);这句话就出错了,

估计是刚启动childwindow时,DisplayStyleGrid并没有实例化,

把动态创建的代码放到一个BUTTON中执行,就可以正常执行.

为什么在这个事件ColumnComboBox_SelectionChanged中不行?

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Answer 5

我跟踪了一下
在ColumnComboBox_SelectionChanged事件中,DisplayStyleGrid为null

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Answer 6

控件是这样的,
<ComboBox x:Name="ColumnComboBox" VerticalAlignment="Center" Width="80" SelectionChanged="ColumnComboBox_SelectionChanged">
                <ComboBoxItem Content="1列" Tag="1"></ComboBoxItem>
                <ComboBoxItem Content="2列" Tag="2" IsSelected="True"></ComboBoxItem>
                <ComboBoxItem Content="3列" Tag="3"></ComboBoxItem>
                <ComboBoxItem Content="4列" Tag="4"></ComboBoxItem>
            </ComboBox>

---

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Answer 7

我把 IsSelected="True"去掉,就不会出错,但去掉后,就不能默认一个选择了

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Answer 8

这个我遇到过。是因为你刚创建控件时，ComboBox  就加入对象， ComboBox  就会触发 SelectionChanged这个事件。因为他会选择一个 “项”
而这时候你的其它对像都还没有创建，数据也没有加载进去。所以会报错！昨晚我用ListBox的时候发现的，呵呵！
你可以考虑用一个变量来标记是否是第一次创建。

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努力！写一个js解析器,一个svg插件,一个绘图程序,做好自己,呵呵～！

Answer 9

我把 IsSelected="True"去掉,就不会出错,但去掉后,就不能默认一个选择了

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aaaa

触发SelectionChanged时,在内容里加一个判断

if(ColumnComboBox.Items != null)
  if(ColumnComboBox.SelectItem !=null)
  {
  }

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如果您觉得对您有帮助，请在“是否有帮助”点“是”；如果你觉得回复很满意，请“标记为已解答”

Answer 10

ColumnComboBox.SelectItem !=null
对，加这个更合理一些

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努力！写一个js解析器,一个svg插件,一个绘图程序,做好自己,呵呵～！

Answer 11

OK,对Grid控件判断是否为空.

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