android edittext 去边框 去下划线

EditText的background属性设置为@null就搞定了：android:background="@null"
style属性倒是可加可不加

附原文：
@SlumberMachine, that's a great observation! But, it seems that there is more to making a TextView editable than just setting android:editable="true". It has to do with the "input method" - what ever that is - and that is where the real difference between TextView and EditText lies. TextView was designed with an EditText in mind, that's for sure. One would have to look at the EditText source code and probably EditText style to see what's really going on there. Documentation is simply not enough.

I have asked the same question back at android-developers group, and got a satisfactory answer. This is what you have to do:

XML:
<EditText android:id="@+id/title" android:layout_width="fill_parent"
     style="?android:attr/textViewStyle"
     android:background="@null" android:textColor="@null"/>

Instead of style="?android:attr/textViewStyle" you can also write style="@android:style/Widget.TextView", don't ask me why and what it means.