ドキュメント > Androidアプリケーション構築のチュートリアル > エクササイズ1

チュートリアル：ノートパッドエクササイズ1

• ListActivities の基本、メニューオプションの作成・操作の基本
• SQLite データベース内のノートへのアクセス/保存方法
• ArrayAdapter （ListView にバインドするためのもっともシンプルな方法の一つ）を用いてデータを ListView にバインドする方法
• リストビューの配置の仕方やアクティビティメニューへのアイテムの追加のやり方、アクティビティがアクティビティメニューアイテムをどのように扱うか、といったスクリーンレイアウトの基本

Step 1

  2. browse ボタンを押し、あなたが本エクササイズをコピーしたフォルダを選択し、その中からNotepadv1を選んでOKを押してください。 
  a. Package Explorer で右クリックし、New->Project... を選択してください。
  b. Android/Android Project を選択し、Next > を押してください。
  c. New Android Project のダイアログで、Create project from existing source(既存のソースからプロジェクトを作成)を選択してください.
  d. browse ボタンを押し、あなたが本エクササイズをコピーしたフォルダを選択し、その中からNotepadv1を選んでOKを押してください。
  e. Project name: 欄に Notepadv1、Location: 欄に選択したパスが表示されることを確認してください。
  f. Finish を押します。
  g. 本エクササイズのプロジェクトが Eclipse の Package Explorer に開かれ準備が完了します。
  h. もし AndroidManifest.xml にエラー表示が出ていたり、Android の zipファイルに関連する問題が表示された場合は、プロジェクトの上で右クリックし、ポップアップから、Android Tools->Fix Project Properties を選択してください。(プロジェクトがライブラリの場所を正しく見ていないので、この操作でそれを修復します。)

Step 2

データへのアクセスと更新について
このエクササイズにおいては、単にSQLiteデータベースを直接使ってデータを保存しますが、実際のアプリケーションでは正当なContentProviderを作成し、処理をカプセル化する方がずっと良いでしょう。
もし興味があれば、content provider やデータの保存/検索/表示などに関する情報をいろいろと見つけることが出来るでしょう。

Layout と activity とについて
ほとんどのActivityはそれに関連付けられたレイアウトを持っています。レイアウトはユーザに対してそのactivityの「顔」となります。今回の例では我々のレイアウトは画面全体を覆いノートの一覧を提供します。
しかし、フルスクリーンレイアウトはActivityにとっての唯一の選択肢ではありません。フローティングレイアウト(たとえばダイアログとか警告のように)が欲しいこともあるでしょうし、レイアウトを全く必要としないこともあるでしょう(使用するレイアウトを決めない場合、activityはユーザに見えなくなります)。

  1. All Android layout files must start with the XML header line: <?xml version="1.0" encoding="utf-8"?>.
  2. Also, the next definition will often (but not always) be a layout definition of some kind, in this case a LinearLayout.
  3. Note also that the xml namespace of Android should always be defined in the top level component or layout in the XML so that android: tags can be used through the rest of the file:

     xmlns:android="http://schemas.android.com/apk/res/android"

   android:layout_width="wrap_content"
   android:layout_height="wrap_content">

 <ListView id="@id/android:list"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>
 <TextView id="@id/android:empty"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:text="@string/no_notes"/>

  1. The ListView and TextView can be thought as two alternative views, only one of which will be displayed at once. ListView will be used when there are notes to be shown, while the TextView (which has a default value of "No Notes Yet!" defined as a string resource, will be displayed if there aren't any notes to display).
  2. The @ in the id strings of the ListView and TextView means that the XML parser should parse and expand the rest of the id string and use an ID resource.
  3. And, the android:list and android:empty are IDs that are already provided for us by the Android platform, empty is used automatically when no data is provided in the list adapter. The List Adapter knows to look for these names specifically by default. Alternatively you could also choose to change the default empty view used by the List Adapter by using the setEmptyView().
     More broadly, the android.R class is a set of predefined resources provided for you by the platform, while your project's R class is the set of resources your project has defined. Resources found in the android.R resource class can be used in the XML files by using the android: name space prefix (as we see here).

  1. Create a new file under res/layout called notes_row.xml.
  2. Add the following contents (note: again the xml header is used, and the first node defines the Android xml namespace)

     <?xml version="1.0" encoding="utf-8"?>
     <TextView id="@+id/text1"
         xmlns:android="http://schemas.android.com/apk/res/android"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"/>
           

  3. This is the view that will be used for each notes title row — it has only one text field in it.
  4. In this case we create a new id called text1. The + after the @ in the id string indicates that the id should be automatically created if it does not already exist, so we are defining text1 on the fly and then using it.
  5. After saving this file, open the R.java class in the project and look at it, you should see new definitions for notes_row and text1 (our new definitions) meaning we can now gain access to these from the our code.

   * onCreate() is called when the activity is started — it is a little like the "main" method for the activity. We use this to set up resources and state for the activity when it is running
   * onCreateOptionsMenu() is used to populate the menu for the activity. This is shown when the user hits the menu button, and has a list of options they can select (like "Create Note")
   * onOptionsItemSelected() is the other half of the menu equation, it is used to handle events generated from the menu (e.g. when the user selects the "Create Note" item).

  1. call super() with the icicle parameter passed into our method
  2. setContentView to R.layout.notepad_list
  3. Create a new private class field called dbHelper of class DBHelper (before the onCreate method)
  4. Back in the onCreate method, construct a DBHelper instance — assign to the dbHelper field (note, you must pass this into the constructor for DBHelper)
  5. Finally, call a new method -fillData()- gets the data and populates it using the helper, we haven't defined it yet
  6. onCreate() should now look like this:

         @Override
         public void onCreate(Bundle icicle)
         {
             super.onCreate(icicle);
             setContentView(R.layout.notepad_list);
             dbHelper = new DBHelper(this);
             fillData();
         }

     And remember to add the DBHelper field definition (right under the noteNumber definition):

         private DBHelper dbHelper;

  1. In strings.xml resource (under res/values), add a new string for menu_insert with text "Add Item"

     <string name="menu_insert">Add Item</string>, then save the file
  2. Also, you need a menu position constant at the top of the Notepadv1 class (right under the KEY_BODY definition):

     public static final int INSERT_ID = Menu.FIRST;
  3. In the onCreateOptionsMenu() method, add the menu item. Also take care of the result of the super call being returned. The whole method should now look like this:

         @Override
         public boolean onCreateOptionsMenu(Menu menu) {
             boolean result = super.onCreateOptionsMenu(menu);
             menu.add(0, INSERT_ID, R.string.menu_insert);
             return result;
         }
           

  1. The super.onOptionsItemSelected(item) method call goes at the end of this method — we want to catch our events first!
  2. Switch statement on item.getId()
  3. case INSERT_ID:
  4. calls new method createNote()
  5. break at the end of the case
  6. return the result of the superclass onOptionsItemSelected() method at the end
  7. The whole onOptionsItemSelect() method should now look like this:

         @Override
         public boolean onOptionsItemSelected(Item item) {
             switch (item.getId()) {
             case INSERT_ID:
                 createNote();
                 break;
             }
            
             return super.onOptionsItemSelected(item);
         }
         

  1. String noteName = "Note " + noteNumber++; (Construct the name using "Note" and the counter we have defined in the class)
  2. Call dbHelper.createRow() using noteName as the title and "" for the body
  3. Call fillData() method again after adding (inefficient but simple)
  4. The whole createNote() method should look like this:

         private void createNote() {
             String noteName = "Note " + noteNumber++;
             dbHelper.createRow(noteName, "");
             fillData();
         }
           

   private void fillData() {
       // We need a list of strings for the list items
       List<String> items = new ArrayList<String>();

       // Get all of the rows from the database and create the item list
       List<Row> rows = dbHelper.fetchAllRows();
       for (Row row : rows) {
           items.add(row.title);
       }
       
       // Now create an array adapter and set it to display using our row
       ArrayAdapter<String> notes =
           new ArrayAdapter<String>(this, R.layout.notes_row, items);
       setListAdapter(notes);
       
   }

  1. ArrayAdapter needs a List of Strings (List<String>) containing the items to display
  2. The data is read out of the database as rows, and the title field from each row is used to populate the list of strings
  3. We specify the notes_row view we created as the receptacle for the data
  4. If you get compiler errors about classes not being found, ctrl-shift-O or (cmd-shift-O on the mac) to organize imports.

  1. Right click on the Notepadv1 project
  2. From the popup menu, select Run As -> Android Application
  3. If you see a dialog come up, select Android Launcher as the way of running the application (you can also use the link near the top of the dialog to set this as your default for the workspace, this is recommended as it will stop the plugin from asking you this every time)
  4. Add new notes by hitting the menu button and selecting Add Item from the menu