diff options
Diffstat (limited to 'docs/html/resources/tutorials/notepad/notepad-ex3.jd')
| -rw-r--r-- | docs/html/resources/tutorials/notepad/notepad-ex3.jd | 83 |
1 files changed, 46 insertions, 37 deletions
diff --git a/docs/html/resources/tutorials/notepad/notepad-ex3.jd b/docs/html/resources/tutorials/notepad/notepad-ex3.jd index 8737280..2da113f 100644 --- a/docs/html/resources/tutorials/notepad/notepad-ex3.jd +++ b/docs/html/resources/tutorials/notepad/notepad-ex3.jd @@ -36,7 +36,7 @@ notes.</p> <ol> <li>Remove the code in <code>NoteEdit</code> that parses the title and body - from the extras Bundle. + from the extras Bundle. <p>Instead, we are going to use the <code>DBHelper</code> class to access the notes from the database directly. All we need passed into the NoteEdit Activity is a <code>mRowId</code> (but only if we are editing, if creating we pass @@ -57,7 +57,7 @@ if (body != null) { }</pre> </li> </ol> - + <h2>Step 2</h2> <p>Create a class field for a <code>NotesDbAdapter</code> at the top of the NoteEdit class:</p> @@ -67,11 +67,11 @@ if (body != null) { <pre> mDbHelper = new NotesDbAdapter(this);<br> mDbHelper.open();</pre> - + <h2>Step 3</h2> <p>In <code>NoteEdit</code>, we need to check the <var>savedInstanceState</var> for the -<code>mRowId</code>, in case the note +<code>mRowId</code>, in case the note editing contains a saved state in the Bundle, which we should recover (this would happen if our Activity lost focus and then restarted).</p> <ol> @@ -87,11 +87,11 @@ if (body != null) { </pre> with this: <pre> - mRowId = savedInstanceState != null ? savedInstanceState.getLong(NotesDbAdapter.KEY_ROWID) - : null; + mRowId = (savedInstanceState == null) ? null : + (Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID); if (mRowId == null) { - Bundle extras = getIntent().getExtras(); - mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) + Bundle extras = getIntent().getExtras(); + mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) : null; } </pre> @@ -100,10 +100,15 @@ if (body != null) { Note the null check for <code>savedInstanceState</code>, and we still need to load up <code>mRowId</code> from the <code>extras</code> Bundle if it is not provided by the <code>savedInstanceState</code>. This is a ternary operator shorthand - to safely either use the value or null if it is not present. + to safely either use the value or null if it is not present. + </li> + <li> + Note the use of <code>Bundle.getSerializable()</code> instead of + <code>Bundle.getLong()</code>. The latter encoding returns a <code>long</code> primitive and + so can not be used to represent the case when <code>mRowId</code> is <code>null</code>. </li> </ol> - + <h2>Step 4</h2> <p>Next, we need to populate the fields based on the <code>mRowId</code> if we @@ -126,38 +131,38 @@ public void onClick(View view) { }</pre> <p>We will take care of storing the updates or new notes in the database ourselves, using the life-cycle methods.</p> - + <p>The whole <code>onCreate()</code> method should now look like this:</p> <pre> super.onCreate(savedInstanceState); - + mDbHelper = new NotesDbAdapter(this); mDbHelper.open(); - + setContentView(R.layout.note_edit); - + mTitleText = (EditText) findViewById(R.id.title); mBodyText = (EditText) findViewById(R.id.body); - + Button confirmButton = (Button) findViewById(R.id.confirm); - -mRowId = savedInstanceState != null ? savedInstanceState.getLong(NotesDbAdapter.KEY_ROWID) - : null; + +mRowId = (savedInstanceState == null) ? null : + (Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID); if (mRowId == null) { Bundle extras = getIntent().getExtras(); - mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) + mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) : null; } - + populateFields(); - + confirmButton.setOnClickListener(new View.OnClickListener() { public void onClick(View view) { setResult(RESULT_OK); finish(); } - + });</pre> <h2>Step 6</h2> @@ -180,7 +185,7 @@ is an Android convenience method provided to take care of the Cursor life-cycle. and re-create resources as dictated by the Activity life-cycle, so we don't need to worry about doing that ourselves. After that, we just look up the title and body values from the Cursor and populate the View elements with them.</p> - + <h2>Step 7</h2> @@ -189,12 +194,12 @@ and populate the View elements with them.</p> margin-top:1em;padding:0em;width:240px;"> <h2 style="border:0;font-size:12px;padding:.5em .5em .5em 1em;margin:0; background-color:#FFFFDD;">Why handling life-cycle events is important</h2> - <p style="padding-left:.5em;font-size:12px;margin:0; + <p style="padding-left:.5em;font-size:12px;margin:0; padding:.0em .5em .5em 1em;">If you are used to always having control in your applications, you might not understand why all this life-cycle work is necessary. The reason - is that in Android, you are not in control of your Activity, the + is that in Android, you are not in control of your Activity, the operating system is!</p> - <p style="padding-left:.5em;font-size:12px;margin:0; + <p style="padding-left:.5em;font-size:12px;margin:0; padding:.0em .5em .5em 1em;">As we have already seen, the Android model is based around activities calling each other. When one Activity calls another, the current Activity is paused at the very least, and may be killed altogether if the @@ -209,9 +214,9 @@ and populate the View elements with them.</p> out while the call Activity takes over.</p> </div> -<p>Still in the <code>NoteEdit</code> class, we now override the methods - <code>onSaveInstanceState()</code>, <code>onPause()</code> and - <code>onResume()</code>. These are our life-cycle methods +<p>Still in the <code>NoteEdit</code> class, we now override the methods + <code>onSaveInstanceState()</code>, <code>onPause()</code> and + <code>onResume()</code>. These are our life-cycle methods (along with <code>onCreate()</code> which we already have).</p> <p><code>onSaveInstanceState()</code> is called by Android if the @@ -241,8 +246,10 @@ and populate the View elements with them.</p> @Override protected void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); - outState.putLong(NotesDbAdapter.KEY_ROWID, mRowId); + saveState(); + outState.putSerializable(NotesDbAdapter.KEY_ROWID, mRowId); }</pre> + <p>We'll define <code>saveState()</code> next.</p> </li> <li><code> onPause()</code>: @@ -252,7 +259,6 @@ and populate the View elements with them.</p> super.onPause(); saveState(); }</pre> - <p>We'll define <code>saveState()</code> next.</p> </li> <li><code> onResume()</code>: @@ -264,6 +270,10 @@ and populate the View elements with them.</p> }</pre> </li> </ol> +<p>Note that <code>saveState()</code> must be called in both <code>onSaveInstanceState()</code> +and <code>onPause()</code> to ensure that the data is saved. This is because there is no +guarantee that <code>onSaveInstanceState()</code> will be called and because when it <em>is</em> +called, it is called before <code>onPause()</code>.</p> <h2 style="clear:right;">Step 8</h2> @@ -301,19 +311,18 @@ database.</p> necessary. The resulting method should look like this:</p> <pre> @Override -protected void onActivityResult(int requestCode, int resultCode, - Intent intent) { +protected void onActivityResult(int requestCode, int resultCode, Intent intent) { super.onActivityResult(requestCode, resultCode, intent); fillData(); }</pre> <p>Because the other class now does the work, all this has to do is refresh the data.</p> - + <h2>Step 10</h2> <p>Also remove the lines which set the title and body from the - <code>onListItemClick()</code> method (again they are no longer needed, + <code>onListItemClick()</code> method (again they are no longer needed, only the <code>mRowId</code> is):</p> <pre> Cursor c = mNotesCursor; @@ -344,13 +353,13 @@ so that all that should be left in that method is: other occurrences of <code>mNotesCursor</code> in your <code>fillData()</code> method. </ol> <p> -Run it! (use <em>Run As -> Android Application</em> on the project right +Run it! (use <em>Run As -> Android Application</em> on the project right click menu again)</p> <h2>Solution and Next Steps</h2> <p>You can see the solution to this exercise in <code>Notepadv3Solution</code> -from +from the zip file to compare with your own.</p> <p> When you are ready, move on to the <a href="notepad-extra-credit.html">Tutorial |