怎樣將多個richtextbox合幷到一個？解决方案

怎樣將多個richtextbox合幷到一個？
我是這樣做的爲什麽不行？
rich5.TextRTF   =   rich1.TextRTF   &   rich2.TextRTF   &rich3.TextRTF   &rich4.TextRTF,同樣用加號連接也不行！

------解决方案--------------------
Dim STRTMP As String

rich1.SelStart = 1
rich1.SelLength = Len(rich1.Text)
STRTMP = rich1.SelRTF
rich5.SelRTF = STRTMP
rich2.SelStart = 1
rich2.SelLength = Len(rich2.Text)
STRTMP =rich2.SelRTF
rich5.SelRTF = STRTMP
……