What is the purpose of the method showSoftInput in class InputMethodManager? I am new to android, and well for me the documentation is not very clear :
Explicitly request that the current input method's soft input area be shown to the user, if needed. Call this if the user interacts with your view in such a way that they have expressed they would like to start performing input into it.
From what I have understood it opens the keyboard, am I am right? Why should we use this method, doesn't touching an EditText open automatically the keyboard??
No, touching an edit text doesn't automatically open a soft keyboard. That's just the default behavior. Under the hood, when you touch the edit text a series of events occurs. Eventually the Android framework will call showSoftInput on the IMS of the keyboard. This is the keyboard's chance to decide it doesn't want to show for some reason and return false if it is not shown. For example, I believe at Swype we overrode this not to show the keyboard if there was a hardware keyboard on the device already slid out, on the theory they then wanted to use the hardware keyboard.
Most of the time you're just going to either use the default implementation here, or do a few minor checks then fall back to the default implementation.