Using Java to Add the Contents of two EditText views in Android
That code is a bit dangerous. Integer.valueOf() can throw NumberFormatException which you make no effort to catch. This will happen if you have commas in numbers or non-digit characters. Your other comments are also very important.

As for simplifying the method, it is not good that you call findViewById 3 times every time you press a button. I would store references to editText1, editText2 and textView externally (of this method), as then you can reuse all three here and elsewhere in your code with subtract/multiply etc. You can then remove three lines of code and just have:

Integer s = Integer.valueOf(et1.getText().toString()) + Integer.valueOf(et2.getText().toString());
tv.setText(s.toString());


Remember that you should probably wrap the code in a try catch block unless you can guarantee the text field will only contain decimal numbers. Also, add in your overflow/underflow logic as well.