Responding to Input Android Way

OK, so one way or another we have a text field and a button on the screen. To round off the section that showed how to build a user-interface the Android way, I'll show you how to respond to the button and get the text from the EditText.

The Android way is slightly different if you built the UI programmatically or using XML so I'll need to show you both ways. Also, there's a mixed way to do it that we'll look at too.

Respond to the Send Button

The XML way

To use this attribute, we just specify the name of a method in the activity that we want to call like this:

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send"
    android:onClick="sendMessage" />

Then all we need to do is add the sendMessage method to the activity:

def sendMessage(view)
end

As an easy way to test that our button is hooked up as expected, we'll have it create a toast like so:

def sendMessage(view)
  message = 'Howdy'
  duration = Java::android.widget.TOAST::LENGTH_SHORT
  toast = Java::android.widget.TOAST.makeText(self, message, duration)
  toast.show()
end

And that's all there is to it!

The Programmatic Way

Let's pretend like XML doesn't exist and go back to our old app. It's just one file, which I've prettied up a bit since you last saw it:

class FirstAppActivity
  LAYOUT = Java::android.widget.LinearLayout
  EDIT_TEXT = Java::android.widget.EditText
  BUTTON = Java::android.widget.Button

  attr_accessor :layout, :edit_text, :button

  def on_create(bundle)
    super
    create_layout
    create_edit_text
    create_button
    self.content_view = layout
  end

  def create_layout
    @layout = LAYOUT.new(self)
  end

  def create_edit_text
    @edit_text = EDIT_TEXT.new(self)
    edit_text.hint = 'Enter Some Text!'
    layout.add_view edit_text
    layout_params = edit_text.layout_params
    layout_params.weight = 1
  end

  def create_button
    @button = BUTTON.new(self)
    button.text = 'Send'
    layout.add_view button
  end
end

Please note that in the above I used the same substitutions as the Ruboto way (setHint became hint= and getLayoutParams became layout_params). As it turns out, you don't need Ruboto to get these conversions. They come from JRuby too! Neat! It's also important that in the above I call self.content_view= instead of content_view=.

To respond to click events programmatically, we just need to set the onClickListener for the button. The way this works out in the wash is pretty interesting. Take a look:

TOAST = Java::android.widget.Toast

def create_button
  @button = BUTTON.new(self)
  button.text = 'Send'
  layout.add_view button
  button.on_click_listener = proc { howdy }
end

def howdy
  message = 'Howdy'
  duration = TOAST::LENGTH_SHORT
  toast = TOAST.make_text(self, message, duration)
  toast.show
end

The docs will tell you that the setOnClickListener method is just looking for a callback. In Ruby one way to do that is to set the listener to a proc like the above, then whatever is in the proc will get called when the button gets clicked.

Another way is to use the set form of the method and hand it a block:

button.set_on_click_listener { howdy }

A Blended Approach

The last approach that I'll explore, is one where we still declare our UI over in the XML, but instead of attaching an onClick directly, we'll fetch the object from the XML and work with it programmatically. From what I've seen so far, this approach is pretty common to a lot of problem solving in Android land, so let's take a look.

First, we need to fetch the button from the XML. We can get views (which the button is) via the Activity class's findViewById method. This method just needs an identifier integer which we can access again via our resources package R. If we give our button an id like so:

<Button android:id="@+id/send_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/button_send" />

then the integer can be retrieved from the id package. Using the ruboto/package we can get a reference to the button as R.id.send_button. We can use that id to retrieve the view with the findViewById method available to our activity.

Altogether that's:

require 'ruboto/package'

class FirstAppActivity
  TOAST = Java::android.widget.Toast

  def on_create(bundle)
    super
    self.content_view = R.layout.first_layout
    button = find_view_by_id(R.id.send_button)
    button.set_on_click_listener { howdy }
  end

  def howdy
    message = 'Howdy'
    duration = TOAST::LENGTH_SHORT
    toast = TOAST.make_text(self, message, duration)
    toast.show
  end
end