Android ApiDemos example (9): App-& gt; Activity-& gt; Persist

Android provides a variety of data storage methods, the simplest of which is to use Shared Preferences. shared Preferences can store Key/value pairs. Shared Preferences supports accessing boolean, float, long, integer, string. The most common use of Shared Preferences is to store some application Preferences. In addition, onSaveInstanceState () is used to save the UI state.

App-> Activity-> Persistent State uses Shared Preferences to maintain some UI States (the value of TextView ).

Create or modify Shared Preferences by using the getSharedPreferences (String name, int mode) method. Shared Preferences is used to share some data between different activities of a single Application. A single Preferences cannot be used to share data between different applications.

SharedPreferences. Editor is used to add data to Shared Preferences: editor. putXXX (key, value)

[Java]
Protected void onPause (){
Super. onPause ();

SharedPreferences. Editor editor = getPreferences (0). edit ();
Editor. putString ("text", mSaved. getText (). toString ());
Editor. putInt ("selection-start", mSaved. getSelectionStart ());
Editor. putInt ("selection-end", mSaved. getSelectionEnd ());
Editor. commit ();
}
Protected void onPause (){
Super. onPause ();
 
SharedPreferences. Editor editor = getPreferences (0). edit ();
Editor. putString ("text", mSaved. getText (). toString ());
Editor. putInt ("selection-start", mSaved. getSelectionStart ());
Editor. putInt ("selection-end", mSaved. getSelectionEnd ());
Editor. commit ();
}

Read Shared Preference: pref. getXXX (key)

[Java]
Protected void onResume (){
Super. onResume ();

SharedPreferences prefs = getPreferences (0 );
String restoredText = prefs. getString ("text", null );
If (restoredText! = Null ){
MSaved. setText (restoredText, TextView. BufferType. EDITABLE );

Int selectionStart = prefs. getInt ("selection-start",-1 );
Int selectionEnd = prefs. getInt ("selection-end",-1 );
If (selectionStart! =-1 & selectionEnd! =-1 ){
MSaved. setSelection (selectionStart, selectionEnd );
}
}
}
Protected void onResume (){
Super. onResume ();
 
SharedPreferences prefs = getPreferences (0 );
String restoredText = prefs. getString ("text", null );
If (restoredText! = Null ){
MSaved. setText (restoredText, TextView. BufferType. EDITABLE );
 
Int selectionStart = prefs. getInt ("selection-start",-1 );
Int selectionEnd = prefs. getInt ("selection-end",-1 );
If (selectionStart! =-1 & selectionEnd! =-1 ){
MSaved. setSelection (selectionStart, selectionEnd );
}
}
}

 

Persistent State demonstrates how to use Shared Preferences to retain EditText content during Activity restoration. The more general method is to use onSaveInstanceState.

 

Author: mapdigit