| page.title=Notepad Exercise 1 |
| parent.title=Notepad Tutorial |
| parent.link=index.html |
| @jd:body |
| |
| |
| <p><em>In this exercise, you will construct a simple notes list that lets the |
| user add new notes but not edit them. The exercise demonstrates:</em></p> |
| <ul> |
| <li><em>The basics of <code>ListActivities</code> and creating and handling menu |
| options. </em></li> |
| <li><em>How to use a SQLite database to store the notes.</em></li> |
| <li><em>How to bind data from a database cursor into a ListView using a |
| SimpleCursorAdapter.</em></li> |
| <li><em>The basics of screen layouts, including how to lay out a list view, how |
| you can add items to the activity menu, and how the activity handles those menu |
| selections. </em></li> |
| </ul> |
| |
| <div style="float:right;white-space:nowrap"> |
| <span style="color:#BBB;"> |
| [<a href="notepad-ex1.html" style="color:#BBB;">Exercise 1</a>]</span> |
| [<a href="notepad-ex2.html">Exercise 2</a>] |
| [<a href="notepad-ex3.html">Exercise 3</a>] |
| [<a href="notepad-extra-credit.html">Extra Credit</a>] |
| </div> |
| |
| |
| |
| <h2>Step 1</h2> |
| |
| <p>Open up the <code>Notepadv1</code> project in Eclipse.</p> |
| |
| <p><code>Notepadv1</code> is a project that is provided as a starting point. It |
| takes care of some of the boilerplate work that you have already seen if you |
| followed the <a href="{@docRoot}resources/tutorials/hello-world.html">Hello, |
| World</a> tutorial.</p> |
| |
| <ol> |
| <li> |
| Start a new Android Project by clicking <strong>File</strong> > |
| <strong>New</strong> > <strong>Android Project</strong>.</li> |
| <li> |
| In the New Android Project dialog, select <strong>Create project from existing source</strong>.</li> |
| <li> |
| Click <strong>Browse</strong> and navigate to where you copied the <code>NotepadCodeLab</code> |
| (downloaded during <a href="{@docRoot}resources/tutorials/notepad/index.html#preparing">setup</a>) |
| and select <code>Notepadv1</code>.</li> |
| <li> |
| The Project Name and other properties should be automatically filled for you. |
| You must select the Build Target—we recommend selecting a target with the |
| lowest platform version available. Also add an integer to the Min SDK Version field |
| that matches the API Level of the selected Build Target.</li> |
| <li> |
| Click <strong>Finish</strong>. The <code>Notepadv1</code> project should open and be |
| visible in your Eclipse package explorer.</li> |
| </ol> |
| |
| <p>If you see an error about <code>AndroidManifest.xml</code>, or some |
| problems related to an Android zip file, right click on the project and |
| select <strong>Android Tools</strong> > <strong>Fix Project Properties</strong>. |
| (The project is looking in the wrong location for the library file, |
| this will fix it for you.)</p> |
| |
| <h2>Step 2</h2> |
| |
| <div class="sidebox-wrapper"> |
| <div class="sidebox"> |
| <h2>Accessing and modifying data</h2> |
| <p>For this |
| exercise, we are using a SQLite database to store our data. This is useful |
| if only <em>your</em> application will need to access or modify the data. If you wish for |
| other activities to access or modify the data, you have to expose the data using a |
| {@link android.content.ContentProvider ContentProvider}.</p> |
| <p>If you are interested, you can find out more about |
| <a href="{@docRoot}guide/topics/providers/content-providers.html">content providers</a> or the |
| whole |
| subject of <a href="{@docRoot}guide/topics/data/data-storage.html">Data Storage</a>. |
| The NotePad sample in the <code>samples/</code> folder of the SDK also has an example of how |
| to create a ContentProvider.</p> |
| </div> |
| </div> |
| |
| <p>Take a look at the <code>NotesDbAdapter</code> class — this class is provided to |
| encapsulate data access to a SQLite database that will hold our notes data |
| and allow us to update it.</p> |
| <p>At the top of the class are some constant definitions that will be used in the application |
| to look up data from the proper field names in the database. There is also a database creation |
| string defined, which is used to create a new database schema if one doesn't exist already.</p> |
| <p>Our database will have the name <code>data</code>, and have a single table called |
| <code>notes</code>, which in turn has three fields: <code>_id</code>, <code>title</code> and |
| <code>body</code>. The <code>_id</code> is named with an underscore convention used in a number of |
| places inside the Android SDK and helps keep a track of state. The <code>_id</code> |
| usually has to be specified when querying or updating the database (in the column projections |
| and so on). The other two fields are simple text fields that will store data. |
| </p> |
| <p>The constructor for <code>NotesDbAdapter</code> takes a Context, which allows it to communicate with aspects |
| of the Android operating system. This is quite common for classes that need to touch the |
| Android system in some way. The Activity class implements the Context class, so usually you will just pass |
| <code>this</code> from your Activity, when needing a Context.</p> |
| <p>The <code>open()</code> method calls up an instance of DatabaseHelper, which is our local |
| implementation of the SQLiteOpenHelper class. It calls <code>getWritableDatabase()</code>, |
| which handles creating/opening a database for us.</p> |
| <p><code>close()</code> just closes the database, releasing resources related to the |
| connection.</p> |
| <p><code>createNote()</code> takes strings for the title and body of a new note, |
| then creates that note in the database. Assuming the new note is created successfully, the |
| method also returns the row <code>_id</code> value for the newly created note.</p> |
| <p><code>deleteNote()</code> takes a <var>rowId</var> for a particular note, and deletes that note from |
| the database.</p> |
| |
| <p><code>fetchAllNotes()</code> issues a query to return a {@link android.database.Cursor} over all notes in the |
| database. The <code>query()</code> call is worth examination and understanding. The first field is the |
| name of the database table to query (in this case <code>DATABASE_TABLE</code> is "notes"). |
| The next is the list of columns we want returned, in this case we want the <code>_id</code>, |
| <code>title</code> and <code>body</code> columns so these are specified in the String array. |
| The remaining fields are, in order: <code>selection</code>, |
| <code>selectionArgs</code>, <code>groupBy</code>, <code>having</code> and <code>orderBy</code>. |
| Having these all <code>null</code> means we want all data, need no grouping, and will take the default |
| order. See {@link android.database.sqlite.SQLiteDatabase SQLiteDatabase} for more details.</p> |
| <p class="note"><b>Note:</b> A Cursor is returned rather than a collection of rows. This allows |
| Android to use resources efficiently -- instead of putting lots of data straight into memory |
| the cursor will retrieve and release data as it is needed, which is much more efficient for |
| tables with lots of rows.</p> |
| |
| <p><code>fetchNote()</code> is similar to <code>fetchAllNotes()</code> but just gets one note |
| with the <var>rowId</var> we specify. It uses a slightly different version of the |
| {@link android.database.sqlite.SQLiteDatabase} <code>query()</code> method. |
| The first parameter (set <em>true</em>) indicates that we are interested |
| in one distinct result. The <var>selection</var> parameter (the fourth parameter) has been specified to search |
| only for the row "where _id =" the <var>rowId</var> we passed in. So we are returned a Cursor on |
| the one row.</p> |
| <p>And finally, <code>updateNote()</code> takes a <var>rowId</var>, <var>title</var> and <var>body</var>, and uses a |
| {@link android.content.ContentValues ContentValues} instance to update the note of the given |
| <var>rowId</var>.</p> |
| |
| <h2 style="clear:right;">Step 3</h2> |
| |
| <div class="sidebox-wrapper"> |
| <div class="sidebox"> |
| <h2>Layouts and activities</h2> |
| <p>Most Activity classes will have a layout associated with them. The layout |
| will be the "face" of the Activity to the user. In this case our layout will |
| take over the whole screen and provide a list of notes.</p> |
| <p>Full screen layouts are not the only option for an Activity however. You |
| might also want to use a <a |
| href="{@docRoot}resources/faq/commontasks.html#floatingorfull">floating |
| layout</a> (for example, a <a |
| href="{@docRoot}resources/faq/commontasks.html#dialogsandalerts">dialog |
| or alert</a>), |
| or perhaps you don't need a layout at all (the Activity will be invisible |
| to the user unless you specify some kind of layout for it to use).</p> |
| </div> |
| </div> |
| |
| <p>Open the <code>notepad_list.xml</code> file in <code>res/layout</code> |
| and |
| take a look at it. (You may have to |
| hit the <em>xml</em> tab, at the bottom, in order to view the XML markup.)</p> |
| |
| <p>This is a mostly-empty layout definition file. Here are some |
| things you should know about a layout file:</p> |
| |
| |
| <ul> |
| <li> |
| All Android layout files must start with the XML header line: |
| <code><?xml version="1.0" encoding="utf-8"?></code>. </li> |
| <li> |
| The next definition will often (but not always) be a layout |
| definition of some kind, in this case a <code>LinearLayout</code>. </li> |
| <li> |
| The XML namespace of Android should always be defined in |
| the top level component or layout in the XML so that <code>android:</code> tags can |
| be used through the rest of the file: |
| <p><code>xmlns:android="http://schemas.android.com/apk/res/android"</code></p> |
| </li> |
| </ul> |
| |
| <h2 style="clear:right;">Step 4</h2> |
| <p>We need to create the layout to hold our list. Add code inside |
| of the <code>LinearLayout</code> element so the whole file looks like this: </p> |
| <pre> |
| <?xml version="1.0" encoding="utf-8"?> |
| <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" |
| android:layout_width="wrap_content" |
| android:layout_height="wrap_content"> |
| |
| <ListView android:id="@android:id/list" |
| android:layout_width="wrap_content" |
| android:layout_height="wrap_content"/> |
| <TextView android:id="@android:id/empty" |
| android:layout_width="wrap_content" |
| android:layout_height="wrap_content" |
| android:text="@string/no_notes"/> |
| |
| </LinearLayout> |
| </pre> |
| <ul> |
| <li> |
| The <strong>@</strong> symbol in the id strings of the <code>ListView</code> and |
| <code>TextView</code> tags means |
| that the XML parser should parse and expand the rest of |
| the id string and use an ID resource.</li> |
| <li> |
| The <code>ListView</code> and <code>TextView</code> 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 in <code>res/values/strings.xml</code>) will be displayed if there |
| aren't any notes to display.</li> |
| <li>The <code>list</code> and <code>empty</code> IDs are |
| provided for us by the Android platform, so, we must |
| prefix the <code>id</code> with <code>android:</code> (e.g., <code>@android:id/list</code>).</li> |
| <li>The View with the <code>empty</code> id is used |
| automatically when the {@link android.widget.ListAdapter} has no data for the ListView. The |
| ListAdapter knows to look for this name by default. Alternatively, you could change the |
| default empty view by using {@link android.widget.AdapterView#setEmptyView(View)} |
| on the ListView. |
| <p> |
| More broadly, the <code>android.R</code> class is a set of predefined |
| resources provided for you by the platform, while your project's |
| <code>R</code> class is the set of resources your project has defined. |
| Resources found in the <code>android.R</code> resource class can be |
| used in the XML files by using the <code>android:</code> name space prefix |
| (as we see here).</p> |
| </li> |
| </ul> |
| |
| <h2 style="clear:right;">Step 5</h2> |
| |
| <div class="sidebox-wrapper"> |
| <div class="sidebox"> |
| <h2>Resources and the R class</h2> |
| <p>The folders under res/ in the Eclipse project are for resources. |
| There is a <a href="{@docRoot}resources/faq/commontasks.html#filelist">specific structure</a> |
| to the |
| folders and files under res/.</p> |
| <p>Resources defined in these folders and files will have |
| corresponding entries in the R class allowing them to be easily accessed |
| and used from your application. The R class is automatically generated using the contents |
| of the res/ folder by the eclipse plugin (or by aapt if you use the command line tools). |
| Furthermore, they will be bundled and deployed for you as part of the application.</p> |
| </p> |
| </div> |
| </div> |
| |
| <p>To make the list of notes in the ListView, we also need to define a View for each row:</p> |
| <ol> |
| <li> |
| Create a new file under <code>res/layout</code> called |
| <code>notes_row.xml</code>. </li> |
| <li> |
| Add the following contents (note: again the XML header is used, and the |
| first node defines the Android XML namespace)<br> |
| <pre style="overflow:auto"> |
| <?xml version="1.0" encoding="utf-8"?> |
| <TextView android:id="@+id/text1" |
| xmlns:android="http://schemas.android.com/apk/res/android" |
| android:layout_width="wrap_content" |
| android:layout_height="wrap_content"/></pre> |
| <p> |
| This is the View that will be used for each notes title row — it has only |
| one text field in it. </p> |
| <p>In this case we create a new id called <code>text1</code>. The |
| <strong>+</strong> after the <strong>@</strong> in the id string indicates that the id should |
| be automatically created as a resource if it does not already exist, so we are defining |
| <code>text1</code> on the fly and then using it.</p> |
| </li> |
| <li>Save the file.</li> |
| </ol> |
| <p>Open the <code>R.java</code> class in the |
| project and look at it, you should see new definitions for |
| <code>notes_row</code> and <code>text1</code> (our new definitions) |
| meaning we can now gain access to these from the our code. </p> |
| |
| <h2 style="clear:right;">Step 6</h2> |
| <p>Next, open the <code>Notepadv1</code> class in the source. In the following steps, we are going to |
| alter this class to become a list adapter and display our notes, and also |
| allow us to add new notes.</p> |
| |
| <p><code>Notepadv1</code> will inherit from a subclass |
| of <code>Activity</code> called a <code>ListActivity</code>, |
| which has extra functionality to accommodate the kinds of |
| things you might want to do with a list, for |
| example: displaying an arbitrary number of list items in rows on the screen, |
| moving through the list items, and allowing them to be selected.</p> |
| |
| <p>Take a look through the existing code in <code>Notepadv1</code> class. |
| There is a currently an unused private field called <code>mNoteNumber</code> that |
| we will use to create numbered note titles.</p> |
| <p>There are also three override methods defined: |
| <code>onCreate</code>, <code>onCreateOptionsMenu</code> and |
| <code>onOptionsItemSelected</code>; we need to fill these |
| out:</p> |
| <ul> |
| <li><code>onCreate()</code> is called when the activity is |
| started — it is a little like the "main" method for an Activity. We use |
| this to set up resources and state for the activity when it is |
| running.</li> |
| <li><code>onCreateOptionsMenu()</code> 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"). </li> |
| <li><code>onOptionsItemSelected()</code> 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). |
| </li> |
| </ul> |
| |
| <h2>Step 7</h2> |
| <p>Change the inheritance of <code>Notepadv1</code> from |
| <code>Activity</code> |
| to <code>ListActivity</code>:</p> |
| <pre>public class Notepadv1 extends ListActivity</pre> |
| <p>Note: you will have to import <code>ListActivity</code> into the |
| Notepadv1 |
| class using Eclipse, <strong>ctrl-shift-O</strong> on Windows or Linux, or |
| <strong>cmd-shift-O</strong> on the Mac (organize imports) will do this for you |
| after you've written the above change.</p> |
| |
| <h2>Step 8</h2> |
| <p>Fill out the body of the <code>onCreate()</code> method.</p> |
| <p>Here we will set the title for the Activity (shown at the top of the |
| screen), use the <code>notepad_list</code> layout we created in XML, |
| set up the <code>NotesDbAdapter</code> instance that will |
| access notes data, and populate the list with the available note |
| titles:</p> |
| <ol> |
| <li> |
| In the <code>onCreate</code> method, call <code>super.onCreate()</code> with the |
| <code>savedInstanceState</code> parameter that's passed in.</li> |
| <li> |
| Call <code>setContentView()</code> and pass <code>R.layout.notepad_list</code>.</li> |
| <li> |
| At the top of the class, create a new private class field called <code>mDbHelper</code> of class |
| <code>NotesDbAdapter</code>. |
| </li> |
| <li> |
| Back in the <code>onCreate</code> method, construct a new |
| <code>NotesDbAdapter</code> |
| instance and assign it to the <code>mDbHelper</code> field (pass |
| <code>this</code> into the constructor for <code>DBHelper</code>) |
| </li> |
| <li> |
| Call the <code>open()</code> method on <code>mDbHelper</code> to open (or create) the |
| database. |
| </li> |
| <li> |
| Finally, call a new method <code>fillData()</code>, which will get the data and |
| populate the ListView using the helper — we haven't defined this method yet. </li> |
| </ol> |
| <p> |
| <code>onCreate()</code> should now look like this:</p> |
| <pre> |
| @Override |
| public void onCreate(Bundle savedInstanceState) { |
| super.onCreate(savedInstanceState); |
| setContentView(R.layout.notepad_list); |
| mDbHelper = new NotesDbAdapter(this); |
| mDbHelper.open(); |
| fillData(); |
| }</pre> |
| <p>And be sure you have the <code>mDbHelper</code> field definition (right |
| under the mNoteNumber definition): </p> |
| <pre> private NotesDbAdapter mDbHelper;</pre> |
| |
| <h2>Step 9</h2> |
| |
| <div class="sidebox-wrapper"> |
| <div class="sidebox"> |
| <h2>More about menus</h2> |
| <p>The notepad application we are constructing only scratches the |
| surface with <a href="{@docRoot}resources/faq/commontasks.html#addmenuitems">menus</a>. </p> |
| <p>You can also <a href="{@docRoot}resources/faq/commontasks.html#menukeyshortcuts">add |
| shortcut keys for menu items</a>, <a |
| href="{@docRoot}resources/faq/commontasks.html#menukeyshortcuts">create |
| submenus</a> and even <a href="{@docRoot}resources/faq/commontasks.html#addingtoothermenus">add |
| menu items to other applications!</a>. </p> |
| </div> |
| </div> |
| |
| <p>Fill out the body of the <code>onCreateOptionsMenu()</code> method.</p> |
| |
| <p>We will now create the "Add Item" button that can be accessed by pressing the menu |
| button on the device. We'll specify that it occupy the first position in the menu.</p> |
| |
| <ol> |
| <li> |
| In <code>strings.xml</code> resource (under <code>res/values</code>), add |
| a new string named "menu_insert" with its value set to <code>Add Item</code>: |
| <pre><string name="menu_insert">Add Item</string></pre> |
| <p>Then save the file and return to <code>Notepadv1</code>.</p> |
| </li> |
| <li>Create a menu position constant at the top of the class: |
| <pre>public static final int INSERT_ID = Menu.FIRST;</pre> |
| </li> |
| <li>In the <code>onCreateOptionsMenu()</code> method, change the |
| <code>super</code> call so we capture the boolean return as <code>result</code>. We'll return this value at the end.</li> |
| <li>Then add the menu item with <code>menu.add()</code>.</li> |
| </ol> |
| <p>The whole method should now look like this: |
| <pre> |
| @Override |
| public boolean onCreateOptionsMenu(Menu menu) { |
| boolean result = super.onCreateOptionsMenu(menu); |
| menu.add(0, INSERT_ID, 0, R.string.menu_insert); |
| return result; |
| }</pre> |
| <p>The arguments passed to <code>add()</code> indicate: a group identifier for this menu (none, |
| in this case), a unique ID (defined above), the order of the item (zero indicates no preference), |
| and the resource of the string to use for the item.</p> |
| |
| <h2 style="clear:right;">Step 10</h2> |
| <p>Fill out the body of the <code>onOptionsItemSelected()</code> method:</p> |
| <p>This is going |
| to handle our new "Add Note" menu item. When this is selected, the |
| <code>onOptionsItemSelected()</code> method will be called with the |
| <code>item.getId()</code> set to <code>INSERT_ID</code> (the constant we |
| used to identify the menu item). We can detect this, and take the |
| appropriate actions:</p> |
| <ol> |
| <li> |
| The <code>super.onOptionsItemSelected(item)</code> method call goes at the |
| end of this method — we want to catch our events first! </li> |
| <li> |
| Write a switch statement on <code>item.getItemId()</code>. |
| <p>In the case of <var>INSERT_ID</var>, call a new method, <code>createNote()</code>, |
| and return true, because we have handled this event and do not want to |
| propagate it through the system.</p> |
| </li> |
| <li>Return the result of the superclass' <code>onOptionsItemSelected()</code> |
| method at the end.</li> |
| </ol> |
| <p> |
| The whole <code>onOptionsItemSelect()</code> method should now look like |
| this:</p> |
| <pre> |
| @Override |
| public boolean onOptionsItemSelected(MenuItem item) { |
| switch (item.getItemId()) { |
| case INSERT_ID: |
| createNote(); |
| return true; |
| } |
| |
| return super.onOptionsItemSelected(item); |
| }</pre> |
| |
| <h2>Step 11</h2> |
| <p>Add a new <code>createNote()</code> method:</p> |
| <p>In this first version of |
| our application, <code>createNote()</code> is not going to be very useful. |
| We will simply |
| create a new note with a title assigned to it based on a counter ("Note 1", |
| "Note 2"...) and with an empty body. At present we have no way of editing |
| the contents of a note, so for now we will have to be content making one |
| with some default values:</p> |
| <ol> |
| <li>Construct the name using "Note" and the counter we defined in the class: <code> |
| String noteName = "Note " + mNoteNumber++</code></li> |
| <li> |
| Call <code>mDbHelper.createNote()</code> using <code>noteName</code> as the |
| title and <code>""</code> for the body |
| </li> |
| <li> |
| Call <code>fillData()</code> to populate the list of notes (inefficient but |
| simple) — we'll create this method next.</li> |
| </ol> |
| <p> |
| The whole <code>createNote()</code> method should look like this: </p> |
| <pre> |
| private void createNote() { |
| String noteName = "Note " + mNoteNumber++; |
| mDbHelper.createNote(noteName, ""); |
| fillData(); |
| }</pre> |
| |
| |
| <h2>Step 12</h2> |
| <div class="sidebox-wrapper"> |
| <div class="sidebox"> |
| <h2>List adapters</h2> |
| <p>Our example uses a {@link android.widget.SimpleCursorAdapter |
| SimpleCursorAdapter} to bind a database {@link android.database.Cursor Cursor} |
| into a ListView, and this is a common way to use a {@link android.widget.ListAdapter |
| ListAdapter}. Other options exist like {@link android.widget.ArrayAdapter ArrayAdapter} which |
| can be used to take a List or Array of in-memory data and bind it in to |
| a list as well.</p> |
| </div> |
| </div> |
| |
| <p>Define the <code>fillData()</code> method:</p> |
| <p>This |
| method uses <code>SimpleCursorAdapter,</code> which takes a database <code>Cursor</code> |
| and binds it to fields provided in the layout. These fields define the row elements of our list |
| (in this case we use the <code>text1</code> field in our |
| <code>notes_row.xml</code> layout), so this allows us to easily populate the list with |
| entries from our database.</p> |
| <p>To do this we have to provide a mapping from the <code>title</code> field in the returned Cursor, to |
| our <code>text1</code> TextView, which is done by defining two arrays: the first a string array |
| with the list of columns to map <em>from</em> (just "title" in this case, from the constant |
| <code>NotesDbAdapter.KEY_TITLE</code>) and, the second, an int array |
| containing references to the views that we'll bind the data <em>into</em> |
| (the <code>R.id.text1</code> TextView).</p> |
| <p>This is a bigger chunk of code, so let's first take a look at it:</p> |
| |
| <pre> |
| private void fillData() { |
| // Get all of the notes from the database and create the item list |
| Cursor c = mDbHelper.fetchAllNotes(); |
| startManagingCursor(c); |
| |
| String[] from = new String[] { NotesDbAdapter.KEY_TITLE }; |
| int[] to = new int[] { R.id.text1 }; |
| |
| // Now create an array adapter and set it to display using our row |
| SimpleCursorAdapter notes = |
| new SimpleCursorAdapter(this, R.layout.notes_row, c, from, to); |
| setListAdapter(notes); |
| }</pre> |
| |
| <p>Here's what we've done:</p> |
| <ol> |
| <li> |
| After obtaining the Cursor from <code>mDbHelper.fetchAllNotes()</code>, we |
| use an Activity method called |
| <code>startManagingCursor()</code> that allows Android to take care of the |
| Cursor lifecycle instead of us needing to worry about it. (We will cover the implications |
| of the lifecycle in exercise 3, but for now just know that this allows Android to do some |
| of our resource management work for us.)</li> |
| <li> |
| Then we create a string array in which we declare the column(s) we want |
| (just the title, in this case), and an int array that defines the View(s) |
| to which we'd like to bind the columns (these should be in order, respective to |
| the string array, but here we only have one for each).</li> |
| <li> |
| Next is the SimpleCursorAdapter instantiation. |
| Like many classes in Android, the SimpleCursorAdapter needs a Context in order to do its |
| work, so we pass in <code>this</code> for the context (since subclasses of Activity |
| implement Context). We pass the <code>notes_row</code> View we created as the receptacle |
| for the data, the Cursor we just created, and then our arrays.</li> |
| </ol> |
| <p> |
| In the future, remember that the mapping between the <strong>from</strong> columns and <strong>to</strong> resources |
| is done using the respective ordering of the two arrays. If we had more columns we wanted |
| to bind, and more Views to bind them in to, we would specify them in order, for example we |
| might use <code>{ NotesDbAdapter.KEY_TITLE, NotesDbAdapter.KEY_BODY }</code> and |
| <code>{ R.id.text1, R.id.text2 }</code> to bind two fields into the row (and we would also need |
| to define text2 in the notes_row.xml, for the body text). This is how you can bind multiple fields |
| into a single row (and get a custom row layout as well).</p> |
| <p> |
| If you get compiler errors about classes not being found, ctrl-shift-O or |
| (cmd-shift-O on the mac) to organize imports. |
| </p> |
| |
| <h2 style="clear:right;">Step 13</h2> |
| <p>Run it! |
| <ol> |
| <li> |
| Right click on the <code>Notepadv1</code> project.</li> |
| <li> |
| From the popup menu, select <strong>Run As</strong> > |
| <strong>Android Application</strong>.</li> |
| <li> |
| 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).</li> |
| <li>Add new notes by hitting the menu button and selecting <em>Add |
| Item</em> from the menu.</li> |
| </ol> |
| |
| <h2 style="clear:right;">Solution and Next Steps</h2> |
| <p>You can see the solution to this class in <code>Notepadv1Solution</code> |
| from |
| the zip file to compare with your own.</p> |
| |
| <p>Once you are ready, move on to <a href="notepad-ex2.html">Tutorial |
| Exercise 2</a> to add the ability to create, edit and delete notes.</p> |
| |