WPF组合框：当尝试输入长度>组合框宽度的文本时，光标超出范围

I am working with editable combobox where text can be entered in the textbox area of WPF combobox. When the length of text entered is greater than the width of combobox, the cursor still shows outside the combobox and on the form but text is not shown. Is there anyway to restrict the cursor from not moving out of the combobox?I am working with editable combobox where text