如果您使用换行符，那么您的文本框可能设置为多行:

If you have used a newline, then presumably your text box is set as multiline:

TextBox2.Text = TextBox1.Lines[0];

将在Environment.NewLine上Textbox1的内容，然后
将结果字符串[]中的第一项分配给Textbox2.

Split the content of Textbox1 on Environment.NewLine and then
assign the first item in the resulting string[] to Textbox2.

string[] textbox1SplitValues = Textbox1.Text.Split(Environment.NewLine);
if( textbox1SplitValues.Length > 0 )
{
   Textbox2.Text = textbox1SplitValues[0];
}

根据您昨天的问题(如何 [ TextBoxBase.Lines属性 [

Based on your question yesterday (how to break a text file into line by line sentences.[^]) I am assuming that this is a continuation of that process, and there is a better way to do that first step if you want to achieve a good result on this step. Instead of simply applying the results of your initial split from the word doc text to Textbox1.Text, use the Textbox1.Lines property instead. TextBoxBase.Lines Property[^]