My Android Development Cheatsheet

If I had my druthers, I'd spend all my time developing mobile apps. I've always been fascinated with pocket-sized computers, and have owned many through the years. Unfortunately, for most of my life such devices have been little more than toys, and so I've had to focus my expertise on writing code for "real computers".

This is true even now, during the explosion of smartphone and tablet usage. I'm one of those dinosaurs who knows how to use C, C++, MFC, ATL, CORBA, UNIX, and other ancient magic, so there are sometimes a few months of old-school development between mobile-development gigs. I write iOS stuff for fun, so I keep those skills sharp, but Android is something I touch only when I'm being paid to do so. Thus, I have to find a way to quickly get back up to speed when the Android work does come.

This is my little refresher for when I arrive back in Android-land. It may not help you at all.

WARNING: The below was written back when I wrote apps that targeted Android 2.x. A lot of it is obsolete with the 4.x API. Someday maybe I'll update this.

References

Eclipse

  • Downloading Eclipse (get the package for Java developers)
  • Note: A new Mac won't have Java the runtime installed. You will be prompted to download and install it when you try to run Eclipse the first time.
  • Downloading and Installing the SDK
  • Use Ctrl+Space for "Content Assist" (autocomplete)
  • Search -> File... is the only decent multi-file search command. And that's where the multi-file Replace button is hidden.
  • Code templates, key bindings, and other settings are saved per-workspace. They can be exported and imported into other workspaces.

Android SDK

  • Do android update project --path . to prepare a directory for command-line builds. This will create local.properties. To make a release build, do ant all clean release.
  • App Signing. To share a debug.keystore between developers, create it like this: keytool -genkey -keypass android -keystore debug.keystore -alias androiddebugkey -storepass android -validity 1000 -dname "CN=Android Debug,O=Android,C=US"

Compatibility Library

A compatibility library is available to provide newer API features to older API levels.

Application Resources

See http://developer.android.com/guide/topics/resources/index.html

Styles and Themes

Application-specific styles are defined in XML files in the res/values folder of the project. Syntax for style definitions is described here: http://developer.android.com/guide/topics/resources/style-resource.html

The standard Android style and theme definitions can be found in the platforms/android-N/data/res/values folder in the Android SDK (where N is the platform version).

All available style properties are listed here: http://developer.android.com/reference/android/R.attr.html

All available styles are listed here: http://developer.android.com/reference/android/R.style.html

For more on Styles and Themes: http://developer.android.com/guide/topics/ui/themes.html

Assets

These tools help generate assets for Android apps:

Activity Lifecycle

Activities exist in one of three states:

  • Resumed (or Running): activity is in foreground and has user focus
  • Paused: another activity is in the foreground and has focus, but this activity is still visible
  • Stopped: activity is completely obscured, but still maintains state

Lifecycle callbacks:

  • onCreate() - followed by onStart()
  • onRestart() - followed by onStart()
  • onStart()
    • onResume() - followed by onPause()
    • onPause() - followed by onResume() or onStop()
  • onStop() - followed by onDestroy() or onRestart()
  • onDestroy() - final call

Activity is killable after onPause(), onStop(), or onDestroy(). (Only onPause() is "guaranteed" to be called.)

When Activity A starts Activity B:

  1. A's onPause() method executes
  2. B's onCreate(), onStart(), and onResume() methods execute.
  3. If A is no longer visible, its onStop() method executes

onSaveInstanceState(Bundle) will be called if an activity may be killed. If called, it will be called before onStop(), but there are no guarantees about whether it will occur before or after onPause(). Bundle will be passed to onCreate(Bundle) and onRestoreInstanceState(Bundle) if activity is recreated. By default, this mechanism saves/restores states of all views in the hierarchy, as long as each widget has an ID.

Fragments and Loaders

See Fragments and Loaders. Also see http://android-developers.blogspot.com/2011/02/android-30-fragments-api.html.

The compatibility library has support for fragments and loaders. Need to derive class from FragmentActivity and use getSupportFragmentManager() and getSupportLoaderManager().

Menus

For basic implementation of menu triggered by MENU button or action bar, override onCreateOptionsMenu() and onOptionsItemSelected().

To change options menu after creation, override onPrepareOptionsMenu(). On Android 3.0+, need to call invalidateOptionsMenu() to force system to call onPrepareOptionsMenu().

To create context menu for a view, call registerForContextMenu(), then implement onCreateContextMenu() and onContextItemSelected().

More about menus here: http://developer.android.com/guide/topics/ui/menus.html

Dialogs

Override onCreateDialog(int) and maybe onPrepareDialog(int, Dialog). Use the AlertDialog, ProgressDialog, DatePickerDialog, or TimePickerDialog classes, or create custom dialog.

Call showDialog(int) to display the dialog. Call Dialog's dismiss() or activity's dismissDialog(int) to close it. Implement DialogInterface.OnDismissListener and/or DialogInterface.OnCancelListener for notification.

Consider using new fragments API for dialogs.

ListView and ListActivity

R.layout lists standard list item layouts.

CWAC MergeAdapter makes it easy to bind list items to different kinds of data.

Call adapter's notifyDataSetChanged() method when data changes, to force views and observers to update.

Tabs

See the Tab Layout tutorial

Note that newer Android apps should use the ActionBar API rather than old-style tabs.

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