Use Shared Preferences for primitive data · Use internal device storage for private data · Use external storage for large data sets that are not private · Use ...
Quicknav
Quicknav
Design
Develop
Distribute
GooglePlayDeveloperConsole
AndroidDevelopersBlog
AboutAndroid
Android.com
AndroidDevelopers
AndroidOpenSourceProject
close
GetStarted
Style
Patterns
BuildingBlocks
Downloads
Videos
Training
APIGuides
Reference
Tools
GettheSDK
GoogleServices
GooglePlay
Publishing
Promoting
AppQuality
Spotlight
OpenDistribution
Results
Loading...
Training
APIGuides
Reference
Tools
GoogleServices
totop
AppComponents
AppFundamentals
Activities
Fragments
Loaders
TasksandBackStack
Services
BoundServices
AIDL
ContentProviders
ContentProviderBasics
CreatingaContentProvider
CalendarProvider
ContactsProvider
IntentsandIntentFilters
ProcessesandThreads
Permissions
AppWidgets
AndroidManifest
UserInterface
Overview
Layouts
LinearLayout
RelativeLayout
ListView
GridView
InputControls
Buttons
TextFields
Checkboxes
RadioButtons
ToggleButtons
Spinners
Pickers
InputEvents
Menus
ActionBar
Settings
Dialogs
Notifications
Toasts
Search
CreatingaSearchInterface
AddingRecentQuerySuggestions
AddingCustomSuggestions
SearchableConfiguration
DragandDrop
Accessibility
MakingApplicationsAccessible
AccessibilityDeveloperChecklist
BuildingAccessibilityServices
StylesandThemes
CustomComponents
AppResources
Overview
ProvidingResources
AccessingResources
HandlingRuntimeChanges
Localization
ResourceTypes
Animation
ColorStateList
Drawable
Layout
Menu
String
Style
MoreTypes
AnimationandGraphics
Overview
PropertyAnimation
ViewAnimation
DrawableAnimation
CanvasandDrawables
OpenGL
HardwareAcceleration
Computation
Renderscript
AdvancedRenderscript
RuntimeAPIReference
MediaandCamera
MediaPlayback
SupportedMediaFormats
AudioCapture
JetPlayer
Camera
LocationandSensors
LocationandMaps
LocationStrategies
SensorsOverview
MotionSensors
PositionSensors
EnvironmentSensors
Connectivity
Bluetooth
NFC
NFCBasics
AdvancedNFC
Wi-FiDirect
USB
Accessory
Host
SIP
TextandInput
CopyandPaste
CreatinganIME
SpellingChecker
DataStorage
StorageOptions
DataBackup
AppInstallLocation
Administration
DevicePolicies
WebApps
Overview
TargetingScreensfromWebApps
BuildingWebAppsinWebView
DebuggingWebApps
BestPracticesforWebApps
BestPractices
BewährteVerfahren
Prácticasrecomendadas
Meilleurespratiques
Bestpractice
ベストプラクティス
最佳实践
最佳實務
Compatibility
SupportingMultipleScreens
DistributingtoSpecificScreens
ScreenCompatibilityMode
SupportingTabletsandHandsets
StorageOptions
Storagequickview
UseSharedPreferencesforprimitivedata
Useinternaldevicestorageforprivatedata
Useexternalstorageforlargedatasetsthatarenotprivate
UseSQLitedatabasesforstructuredstorage
Inthisdocument
UsingSharedPreferences
UsingtheInternalStorage
UsingtheExternalStorage
UsingDatabases
UsingaNetworkConnection
Seealso
ContentProvidersandContentResolvers
Androidprovidesseveraloptionsforyoutosavepersistentapplicationdata.Thesolutionyou
choosedependsonyourspecificneeds,suchaswhetherthedatashouldbeprivatetoyour
applicationoraccessibletootherapplications(andtheuser)andhowmuchspaceyourdata
requires.
Yourdatastorageoptionsarethefollowing:
SharedPreferences
Storeprivateprimitivedatainkey-valuepairs.
InternalStorage
Storeprivatedataonthedevicememory.
ExternalStorage
Storepublicdataonthesharedexternalstorage.
SQLiteDatabases
Storestructureddatainaprivatedatabase.
NetworkConnection
Storedataonthewebwithyourownnetworkserver.
Androidprovidesawayforyoutoexposeevenyourprivatedatatootherapplications
—withacontent
provider.Acontentproviderisanoptionalcomponentthatexposesread/writeaccessto
yourapplicationdata,subjecttowhateverrestrictionsyouwanttoimpose.Formoreinformation
aboutusingcontentproviders,seethe
ContentProviders
documentation.
UsingSharedPreferences
TheSharedPreferencesclassprovidesageneralframeworkthatallowsyou
tosaveandretrievepersistentkey-valuepairsofprimitivedatatypes.YoucanuseSharedPreferencestosaveanyprimitivedata:booleans,floats,ints,longs,and
strings.Thisdatawillpersistacrossusersessions(evenifyourapplicationiskilled).
UserPreferences
Sharedpreferencesarenotstrictlyforsaving"userpreferences,"suchaswhatringtonea
userhaschosen.Ifyou'reinterestedincreatinguserpreferencesforyourapplication,seePreferenceActivity,whichprovidesanActivityframeworkforyoutocreate
userpreferences,whichwillbeautomaticallypersisted(usingsharedpreferences).
TogetaSharedPreferencesobjectforyourapplication,useoneof
twomethods:
getSharedPreferences()-Usethisifyouneedmultiplepreferencesfilesidentifiedbyname,
whichyouspecifywiththefirstparameter.
getPreferences()-Usethisifyouneed
onlyonepreferencesfileforyourActivity.Becausethiswillbetheonlypreferencesfile
foryourActivity,youdon'tsupplyaname.
Towritevalues:
Calledit()togetaSharedPreferences.Editor.
AddvalueswithmethodssuchasputBoolean()andputString().
Committhenewvalueswithcommit()
Toreadvalues,useSharedPreferencesmethodssuchasgetBoolean()andgetString().
Hereisanexamplethatsavesapreferenceforsilentkeypressmodeina
calculator:
publicclassCalcextendsActivity{
publicstaticfinalStringPREFS_NAME="MyPrefsFile";
@Override
protectedvoidonCreate(Bundlestate){
super.onCreate(state);
...
//Restorepreferences
SharedPreferencessettings=getSharedPreferences(PREFS_NAME,0);
booleansilent=settings.getBoolean("silentMode",false);
setSilent(silent);
}
@Override
protectedvoidonStop(){
super.onStop();
//WeneedanEditorobjecttomakepreferencechanges.
//Allobjectsarefromandroid.context.Context
SharedPreferencessettings=getSharedPreferences(PREFS_NAME,0);
SharedPreferences.Editoreditor=settings.edit();
editor.putBoolean("silentMode",mSilentMode);
//Committheedits!
editor.commit();
}
}
UsingtheInternalStorage
Youcansavefilesdirectlyonthedevice'sinternalstorage.Bydefault,filessaved
totheinternalstorageareprivatetoyourapplicationandotherapplicationscannotaccess
them(norcantheuser).Whentheuseruninstallsyourapplication,thesefilesareremoved.
Tocreateandwriteaprivatefiletotheinternalstorage:
CallopenFileOutput()withthe
nameofthefileandtheoperatingmode.ThisreturnsaFileOutputStream.
Writetothefilewithwrite().
Closethestreamwithclose().
Forexample:
StringFILENAME="hello_file";
Stringstring="helloworld!";
FileOutputStreamfos=openFileOutput(FILENAME,Context.MODE_PRIVATE);
fos.write(string.getBytes());
fos.close();
MODE_PRIVATEwillcreatethefile(orreplaceafileof
thesamename)andmakeitprivatetoyourapplication.Othermodesavailableare:MODE_APPEND,MODE_WORLD_READABLE,andMODE_WORLD_WRITEABLE.
Toreadafilefrominternalstorage:
CallopenFileInput()andpassitthe
nameofthefiletoread.ThisreturnsaFileInputStream.
Readbytesfromthefilewithread().
Thenclosethestreamwithclose().
Tip:Ifyouwanttosaveastaticfileinyourapplicationat
compiletime,savethefileinyourprojectres/raw/directory.Youcanopenitwith
openRawResource(),passingtheR.raw.resourceID.ThismethodreturnsanInputStream
thatyoucanusetoreadthefile(butyoucannotwritetotheoriginalfile).
Savingcachefiles
Ifyou'dliketocachesomedata,ratherthanstoreitpersistently,youshouldusegetCacheDir()toopenaFilethatrepresentstheinternaldirectorywhereyourapplicationshouldsave
temporarycachefiles.
Whenthedeviceis
lowoninternalstoragespace,Androidmaydeletethesecachefilestorecoverspace.However,you
shouldnotrelyonthesystemtocleanupthesefilesforyou.Youshouldalwaysmaintainthecache
filesyourselfandstaywithinareasonablelimitofspaceconsumed,suchas1MB.Whentheuser
uninstallsyourapplication,thesefilesareremoved.
Otherusefulmethods
getFilesDir()
Getstheabsolutepathtothefilesystemdirectorywhereyourinternalfilesaresaved.
getDir()
Creates(oropensanexisting)directorywithinyourinternalstoragespace.
deleteFile()
Deletesafilesavedontheinternalstorage.
fileList()
Returnsanarrayoffilescurrentlysavedbyyourapplication.
UsingtheExternalStorage
EveryAndroid-compatibledevicesupportsashared"externalstorage"thatyoucanuseto
savefiles.Thiscanbearemovablestoragemedia(suchasanSDcard)oraninternal
(non-removable)storage.Filessavedtotheexternalstorageareworld-readableandcan
bemodifiedbytheuserwhentheyenableUSBmassstoragetotransferfilesonacomputer.
It'spossiblethatadeviceusingapartitionofthe
internalstoragefortheexternalstoragemayalsoofferanSDcardslot.Inthiscase,
theSDcardisnotpartoftheexternalstorageandyourappcannotaccessit(theextra
storageisintendedonlyforuser-providedmediathatthesystemscans).
Caution:Externalstoragecanbecomeunavailableiftheusermountsthe
externalstorageonacomputerorremovesthemedia,andthere'snosecurityenforceduponfilesyou
savetotheexternalstorage.Allapplicationscanreadandwritefilesplacedontheexternal
storageandtheusercanremovethem.
Checkingmediaavailability
Beforeyoudoanyworkwiththeexternalstorage,youshouldalwayscallgetExternalStorageState()tocheckwhetherthemediaisavailable.The
mediamightbemountedtoacomputer,missing,read-only,orinsomeotherstate.Forexample,
here'showyoucanchecktheavailability:
booleanmExternalStorageAvailable=false;
booleanmExternalStorageWriteable=false;
Stringstate=Environment.getExternalStorageState();
if(Environment.MEDIA_MOUNTED.equals(state)){
//Wecanreadandwritethemedia
mExternalStorageAvailable=mExternalStorageWriteable=true;
}elseif(Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)){
//Wecanonlyreadthemedia
mExternalStorageAvailable=true;
mExternalStorageWriteable=false;
}else{
//Somethingelseiswrong.Itmaybeoneofmanyotherstates,butallweneed
//toknowiswecanneitherreadnorwrite
mExternalStorageAvailable=mExternalStorageWriteable=false;
}
Thisexamplecheckswhethertheexternalstorageisavailabletoreadandwrite.The
getExternalStorageState()methodreturnsotherstatesthatyou
mightwanttocheck,suchaswhetherthemediaisbeingshared(connectedtoacomputer),ismissing
entirely,hasbeenremovedbadly,etc.Youcanusethesetonotifytheuserwithmoreinformation
whenyourapplicationneedstoaccessthemedia.
Accessingfilesonexternalstorage
Ifyou'reusingAPILevel8orgreater,usegetExternalFilesDir()toopenaFilethatrepresentstheexternalstoragedirectorywhereyoushouldsaveyour
files.Thismethodtakesatypeparameterthatspecifiesthetypeofsubdirectoryyou
want,suchasDIRECTORY_MUSICand
DIRECTORY_RINGTONES(passnulltoreceive
therootofyourapplication'sfiledirectory).Thismethodwillcreatethe
appropriatedirectoryifnecessary.Byspecifyingthetypeofdirectory,you
ensurethattheAndroid'smediascannerwillproperlycategorizeyourfilesinthesystem(for
example,ringtonesareidentifiedasringtonesandnotmusic).Iftheuseruninstallsyour
application,thisdirectoryandallitscontentswillbedeleted.
Ifyou'reusingAPILevel7orlower,usegetExternalStorageDirectory(),toopenaFilerepresentingtherootoftheexternalstorage.Youshouldthenwriteyourdatainthe
followingdirectory:
/Android/data//files/
TheisyourJava-stylepackagename,suchas"com.example.android.app".Iftheuser'sdeviceisrunningAPILevel8orgreaterandthey
uninstallyourapplication,thisdirectoryandallitscontentswillbedeleted.
HidingyourfilesfromtheMediaScanner
Includeanemptyfilenamed.nomediainyourexternalfilesdirectory(notethedot
prefixinthefilename).ThiswillpreventAndroid'smediascannerfromreadingyourmedia
filesandincludingtheminappslikeGalleryorMusic.
Savingfilesthatshouldbeshared
Ifyouwanttosavefilesthatarenotspecifictoyourapplicationandthatshouldnot
bedeletedwhenyourapplicationisuninstalled,savethemtooneofthepublicdirectoriesonthe
externalstorage.Thesedirectorieslayattherootoftheexternalstorage,suchasMusic/,Pictures/,Ringtones/,andothers.
InAPILevel8orgreater,usegetExternalStoragePublicDirectory(),passingitthetypeofpublicdirectoryyouwant,suchas
DIRECTORY_MUSIC,DIRECTORY_PICTURES,
DIRECTORY_RINGTONES,orothers.Thismethodwillcreatethe
appropriatedirectoryifnecessary.
Ifyou'reusingAPILevel7orlower,usegetExternalStorageDirectory()toopenaFilethatrepresents
therootoftheexternalstorage,thensaveyoursharedfilesinoneofthefollowing
directories:
Music/-Mediascannerclassifiesallmediafoundhereasusermusic.
Podcasts/-Mediascannerclassifiesallmediafoundhereasapodcast.
Ringtones/-Mediascannerclassifiesallmediafoundhereasaringtone.
Alarms/-Mediascannerclassifiesallmediafoundhereasanalarmsound.
Notifications/-Mediascannerclassifiesallmediafoundhereasanotification
sound.
Pictures/-Allphotos(excludingthosetakenwiththecamera).
Movies/-Allmovies(excludingthosetakenwiththecamcorder).
Download/-Miscellaneousdownloads.
Savingcachefiles
Ifyou'reusingAPILevel8orgreater,usegetExternalCacheDir()toopenaFilethatrepresentsthe
externalstoragedirectorywhereyoushouldsavecachefiles.Iftheuseruninstallsyour
application,thesefileswillbeautomaticallydeleted.However,duringthelifeofyour
application,youshouldmanagethesecachefilesandremovethosethataren'tneededinorderto
preservefilespace.
Ifyou'reusingAPILevel7orlower,usegetExternalStorageDirectory()toopenaFilethatrepresents
therootoftheexternalstorage,thenwriteyourcachedatainthefollowingdirectory:
/Android/data//cache/
TheisyourJava-stylepackagename,suchas"com.example.android.app".
UsingDatabases
AndroidprovidesfullsupportforSQLitedatabases.
Anydatabasesyoucreatewillbeaccessiblebynametoany
classintheapplication,butnotoutsidetheapplication.
TherecommendedmethodtocreateanewSQLitedatabaseistocreateasubclassofSQLiteOpenHelperandoverridetheonCreate()method,inwhichyou
canexecuteaSQLitecommandtocreatetablesinthedatabase.Forexample:
publicclassDictionaryOpenHelperextendsSQLiteOpenHelper{
privatestaticfinalintDATABASE_VERSION=2;
privatestaticfinalStringDICTIONARY_TABLE_NAME="dictionary";
privatestaticfinalStringDICTIONARY_TABLE_CREATE=
"CREATETABLE"+DICTIONARY_TABLE_NAME+"("+
KEY_WORD+"TEXT,"+
KEY_DEFINITION+"TEXT);";
DictionaryOpenHelper(Contextcontext){
super(context,DATABASE_NAME,null,DATABASE_VERSION);
}
@Override
publicvoidonCreate(SQLiteDatabasedb){
db.execSQL(DICTIONARY_TABLE_CREATE);
}
}
YoucanthengetaninstanceofyourSQLiteOpenHelper
implementationusingtheconstructoryou'vedefined.Towritetoandreadfromthedatabase,call
getWritableDatabase()andgetReadableDatabase(),respectively.Thesebothreturna
SQLiteDatabaseobjectthatrepresentsthedatabaseand
providesmethodsforSQLiteoperations.
AndroiddoesnotimposeanylimitationsbeyondthestandardSQLiteconcepts.Wedorecommend
includinganautoincrementvaluekeyfieldthatcanbeusedasauniqueIDto
quicklyfindarecord.Thisisnotrequiredforprivatedata,butifyou
implementacontentprovider,
youmustincludeauniqueIDusingtheBaseColumns._ID
constant.
YoucanexecuteSQLitequeriesusingtheSQLiteDatabase
query()methods,whichacceptvariousqueryparameters,suchasthetabletoquery,
theprojection,selection,columns,grouping,andothers.Forcomplexqueries,suchas
thosethatrequirecolumnaliases,youshoulduse
SQLiteQueryBuilder,whichprovides
severalconvienentmethodsforbuildingqueries.
EverySQLitequerywillreturnaCursorthatpointstoalltherows
foundbythequery.TheCursorisalwaysthemechanismwithwhich
youcannavigateresultsfromadatabasequeryandreadrowsandcolumns.
ForsampleappsthatdemonstratehowtouseSQLitedatabasesinAndroid,seethe
NotePadand
SearchableDictionary
applications.
Databasedebugging
TheAndroidSDKincludesasqlite3databasetoolthatallowsyoutobrowse
tablecontents,runSQLcommands,andperformotherusefulfunctionsonSQLite
databases.SeeExaminingsqlite3
databasesfromaremoteshelltolearnhowtorunthistool.
UsingaNetworkConnection
Youcanusethenetwork(whenit'savailable)tostoreandretrievedataonyourownweb-based
services.Todonetworkoperations,useclassesinthefollowingpackages:
java.net.*
android.net.*
Previous
Next
Exceptasnoted,thiscontentis
licensedunder
CreativeCommonsAttribution2.5.Fordetailsand
restrictions,seetheContent
License.
AboutAndroid |
Legal |
Support
Android internal storage permission