How to Make Android Apps 17
In this part of my Android tutorial I cover 3 ways to save data. We’ll look at Bundles, onSaveInstanceState, SharedPreferences, and PreferenceActivity. We’ll also be reviewing working with components, Intents, click listeners, onActivityResult and a bunch of other topics.
This will begin a series of tutorials in which I cover everything about Android that I have previously not covered.
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Code From the Video
AndroidManifest.xml
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<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.newthinktank.derekbanas.savingstate" > <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name=".MyActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".SettingsActivity" android:label="@string/title_activity_settings" > </activity> </application> </manifest> |
activity_my.xml
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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MyActivity"> <TextView android:text="@string/notesTextView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:textSize="20sp" android:id="@+id/notesTextView" /> <EditText android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="textMultiLine" android:ems="10" android:id="@+id/notesEditText" android:layout_below="@+id/notesTextView" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" android:layout_marginTop="15dp" android:lines="6" android:maxLines="6" android:hint="@string/notesEditText" android:gravity="top"/> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="109dp" android:text="Settings" android:id="@+id/btnSettings" android:layout_below="@+id/notesEditText" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" /> </RelativeLayout> |
strings.xml
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<?xml version="1.0" encoding="utf-8"?> <resources> <string name="app_name">SavingState</string> <string name="hello_world">Hello world!</string> <string name="action_settings">Settings</string> <string name="notesEditText">Enter notes</string> <string name="notesTextView">Notes</string> <string name="title_activity_settings">SettingsActivity</string> </resources> |
MyActivity.java
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package com.newthinktank.derekbanas.savingstate; import android.app.Activity; import android.content.Context; import android.content.Intent; import android.content.SharedPreferences; import android.graphics.Typeface; import android.os.Bundle; import android.preference.PreferenceManager; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.Button; import android.widget.EditText; public class MyActivity extends Activity { EditText notesEditText; Button btnSettings; private static final int SETTINGS_INFO = 1; // You can define what keys and values are passed to onCreate @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_my); notesEditText = (EditText) findViewById(R.id.notesEditText); // 1. Make sure there is data to retrieve if(savedInstanceState != null){ String notes = savedInstanceState.getString("NOTES"); notesEditText.setText(notes); } // 2. Retrieves the String stored in shared preferences or "EMPTY" if nothing String sPNotes = getPreferences(Context.MODE_PRIVATE).getString("NOTES", "EMPTY"); if(!sPNotes.equals("EMPTY")){ notesEditText.setText(sPNotes); } // 3. Get a reference to the settings button btnSettings = (Button) findViewById(R.id.btnSettings); // 3. If the button is clicked create an intent to open the SettingsActivity class btnSettings.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { Intent intentPreferences = new Intent(getApplicationContext(), SettingsActivity.class); // 3. Start the activity and then pass results to onActivityResult startActivityForResult(intentPreferences, SETTINGS_INFO); } }); } // 3. Called after the settings intent closes @Override protected void onActivityResult(int requestCode, int resultCode, Intent data){ super.onActivityResult(requestCode, resultCode, data); // 3. Check that the intent with the id SETTINGS_INFO called here if(requestCode == SETTINGS_INFO){ updateNoteText(); } } // 3. Update the text changes in the EditText box private void updateNoteText(){ // Shared key value pairs are here SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this); // Check if the checkbox was clicked if(sharedPreferences.getBoolean("pref_text_bold", false)){ // Set the text to bold notesEditText.setTypeface(null, Typeface.BOLD_ITALIC); } else { // If not checked set the text to normal notesEditText.setTypeface(null, Typeface.NORMAL); } // Get the value stored in the list preference or give a value of 16 String textSizeStr = sharedPreferences.getString("pref_text_size", "16"); // Convert the string returned to a float float textSizeFloat = Float.parseFloat(textSizeStr); // Set the text size for the EditText box notesEditText.setTextSize(textSizeFloat); } // 1. Called before Android kills an application, but doesn't protect you // if the user kills the app or restarts the device @Override protected void onSaveInstanceState(Bundle outState) { // Save the value in the EditText using the key NOTES outState.putString("NOTES", notesEditText.getText().toString()); super.onSaveInstanceState(outState); } // 2. Will save key value pairs to SharedPreferences private void saveSettings(){ // SharedPreferences allow you to save data even if the user kills the app // MODE_PRIVATE : Preferences shared only by your app // MODE_WORLD_READABLE : All apps can read // MODE_WORLD_WRITABLE : All apps can write // edit() allows us to enter key vale pairs SharedPreferences.Editor sPEditor = getPreferences(Context.MODE_PRIVATE).edit(); // Add the key "NOTES" and assign it to the value sPEditor.putString("NOTES", notesEditText.getText().toString()); // Save the shared preferences sPEditor.commit(); } // 2. Called if the app is forced to close @Override protected void onStop() { saveSettings(); super.onStop(); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.settings, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } } |
preferences.xml
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<?xml version="1.0" encoding="utf-8"?> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"> <CheckBoxPreference android:key="pref_text_bold" android:title="Make Text Bold" android:summary="Makes the note text bold" android:defaultValue="false" /> <ListPreference android:key="pref_text_size" android:title="Text Size" android:summary="Pick the text size" android:entries="@array/text_size_entries" android:entryValues="@array/text_size_values" android:defaultValue="16"/> </PreferenceScreen> |
arrays.xml
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<?xml version="1.0" encoding="utf-8"?> <resources> <string-array name="text_size_entries"> <item>16 pt</item> <item>18 pt</item> <item>20 pt</item> <item>22 pt</item> <item>24 pt</item> <item>26 pt</item> </string-array> <string-array name="text_size_values"> <item>16</item> <item>18</item> <item>20</item> <item>22</item> <item>24</item> <item>26</item> </string-array> </resources> |
SettingsActivity.java
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package com.newthinktank.derekbanas.savingstate; import android.os.Bundle; import android.preference.PreferenceActivity; public class SettingsActivity extends PreferenceActivity { @SuppressWarnings("deprecation") @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Define the xml file used for preferences addPreferencesFromResource(R.xml.preferences); } } |
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