CS 175/286 - Lecture 4

Cay S. Horstmann

Today's Lecture

• Cinequest
• Making buttons active
• Activities

Making buttons work

• Need to add a listener to the button
• A listener is a method with parameter View and return type void
• Can set in XML:

  <Button ...
      android:text="@string/button_send"
      android:onClick="sendMessage" />

• Can set programmatically:

  ((Button) findViewById(R.id.button2)).setOnClickListener(
     new View.OnClickListener() {
        @Override public void onClick(View arg0) {
           ...
     }});

• I prefer the latter—why mix layout with code?

Changing Activities

• Often, a UI event such as a button click is an indication to switch to a different view.
• You switch to a new view with an intent.
• An intent describes what you want to do, e.g. show a web page, play a movie
• In general, multiple applications can offer to satisfy the intent. It's beyond your control how the intent is satisfied. End-users like this.
• An explicit intent is delivered to a particular activity.

  Intent intent = new Intent(Outerclass.this, ResponseActivity.class);

• Call startActivity(intent) to start new intent.

Activities with Results

• Call startActivityWithResult(intent, requestCode) to start new intent.
• In the called intent, call

  Intent result = new Intent();
  result.putExtra("...", ...);
  setResult(Activity.RESULT_OK, result);
  finish();

  in order to return to the calling intent.
• In the calling intent, provide a handler

  protected void onActivityResult(int requestCode, int resultCode, Intent data)

Reading Before Next Class

• Programming Android Chapter 6 until Wiring up the Controller. Stop just before Listening to the Model.
• Same as for today, but we'll have a quiz on Tuesday

Lab

• Bring your laptop to each class
• You will work with a buddy
• One of you writes code, the other types up answers
• Switch roles each lab
• Submit lab work to github

Making the Buttons Active

1. Start with the solution to the first homework. Solutions can be found on Github. Run git clone git@github.com:sjsu-fall2013-cs175/solutions.git somewhere outside your cs175 repo
2. Copy the homework into cs175/lab04:

   cp -R solutions/hw01 cs175/lab04

3. In Eclipse, select File → New → Project → Android → Android Project from Existing Source select lab04. Then rename the package to edu.sjsu.cs175.lab04 in the Package Explorer. Also rename the package in AndroidManifest.xml and change the app name to Lab 4 in values/strings.xml. (You should make it a habit to do this whenever you make a new lab or homework assignment.)
4. While we are at it, let's banish tabs from our source files. (Don't know why? Read this.) Go to Window → Preferences and type tabs into the search box in the top left corner. Click on Text Editors and click on Insert spaces for tabs. But wait, that's not all. Now click on Java/Editor/Typing, then on the Formatter link, and on Edit. Change the name from Eclipse (default) to CS185C, and change the Tabs poliy to Spaces only. Click on Apply and Ok. Go to MainActivity.java and select Source → Correct Indentation from the menu. Verify that there are now spaces in the file (by deleting a character in an indented line).
5. Select File → New → Other → Android → Android Activity and make a ResponseActivity with all the default options.
6. In the MainActivity, make the first button go to the ResponseActivity when clicked. How did you do that?
7. What happens when you run the program and click the button?
8. What happens when you click the Back button in the emulator?
9. Now make all buttons go to the ResponseActivity. Use a for loop like in the onCreate method.