WPF中扩展器内的RichTextBox 你好

上述代码有效。但是：

<Expander Header="More options" Margin="281,218,39,12">
    <Button Height="29" Width="111"> hello </Button>
</Expander>

你好？

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这是行不通的。为什么？如何进行此操作？

请删除边距并避免设置静态高度和宽度，这样做会有效

<Expander Header="More options" Margin="281,218,39,12">
    <RichTextBox Name="richTextBox1" Margin="100,50,200,30" Height="30" Width="80">
        <FlowDocument>
            <Paragraph>Hi how are you?</Paragraph>
        </FlowDocument>
    </RichTextBox>
</Expander>

你好？

<Expander Header="More options" >
    <RichTextBox Name="richTextBox1" >
        <FlowDocument>
            <Paragraph>Hi how are you?</Paragraph>
        </FlowDocument>
    </RichTextBox>
</Expander>