Can you set graphical layout preview-only text on a TextView?
Yes you can with the design tools extension attributes in Android Studio.
See this page https://developer.android.com/studio/write/tool-attributes.html
Basically you define the tools namespace
xmlns:tools="http://schemas.android.com/tools"
Then use it to set your placeholder text.
<EditText tools:text="John Doe" android:layout_width="wrap_content" android:layout_height="wrap_content" />
This actually works with most (if not all xml attributes).
e.g
tools:visibility="gone"
would set the preview visibility to "gone" but the runtime visibility would be unchanged.
I don't believe there is, the only possible way is when you declare your TextView, you say after, tv.setText("");
this way you will always find it blank at runtime