- Internal Storage
- External Storage
- You don't need any permissions to save files on the internal storage. Your app always has permission to read and write files in its internal storage directory.
To create a new file in one of these directories, you can use the File() constructor, passing the File provided by one of the above methods that specifies your internal storage directory. For example:
File file = new File(context.getFilesDir(), filename);Alternatively, you can call openFileOutput() to get a FileOutputStream that writes to a file in your internal directory. For example, here's how to write some text to a file:
String filename = "myfile";
String string = "Hello world!";
FileOutputStream outputStream;
try {
outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
outputStream.write(string.getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}Or, if you need to cache some files, instead use createTempFile(). For example, the following method extracts the filename from a URL and creates a file with that name in your app's internal cache directory:
public File getTempFile(Context context, String url) {
File file;
try {
String fileName = Uri.parse(url).getLastPathSegment();
file = File.createTempFile(fileName, null, context.getCacheDir());
} catch (IOException e) {
// Error while creating file
}
return file;
}To write to the external storage, you must request the WRITE_EXTERNAL_STORAGE permission in your Android manifest. This implicitly includes permission to read.
<manifest ...>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
...
</manifest>If your app needs to read the external storage (but not write to it), then you will need to declare the READ_EXTERNAL_STORAGE permission.
<manifest ...>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
...
</manifest>/* Checks if external storage is available for read and write */
public boolean isExternalStorageWritable() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
return true;
}
return false;
}
/* Checks if external storage is available to at least read */
public boolean isExternalStorageReadable() {
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state) ||
Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
return true;
}
return false;
}To access a public external storage directory, get a path and create a file calling getExternalStoragePublicDirectory().
File path = Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_PICTURES);
File file = new File(path, "DemoPicture.jpg");To access a private external storage directory, get a path and create a file calling getExternalFilesDir().
File file = new File(getExternalFilesDir(null), "DemoFile.jpg");If you know ahead of time how much data you're saving, you can find out whether sufficient space is available without causing an IOException by calling getFreeSpace() or getTotalSpace(). These methods provide the current available space and the total space in the storage volume, respectively.
You should always delete files that you no longer need. The most straightforward way to delete a file is to have the opened file reference call delete() on itself.
myFile.delete();If the file is saved on internal storage, you can also ask the Context to locate and delete a file by calling deleteFile():
myContext.deleteFile(fileName);Shared preferences allow you to store small amounts of primitive data as key/value pairs in a file on the device.
private String sharedPrefFile =
"com.example.android.hellosharedprefs";
mPreferences = getSharedPreferences(sharedPrefFile, MODE_PRIVATE);You save preferences in the onPause() state of the activity lifecycle using the SharedPreferences.Editor interface.
@Override
protected void onPause() {
super.onPause();
SharedPreferences.Editor preferencesEditor = mPreferences.edit();
preferencesEditor.putInt("count", mCount);
preferencesEditor.putInt("color", mCurrentColor);
preferencesEditor.apply();
}mPreferences = getSharedPreferences(sharedPrefFile, MODE_PRIVATE);
if (savedInstanceState != null) {
mCount = mPreferences.getInt("count", 1);
mShowCount.setText(String.format("%s", mCount));
mCurrentColor = mPreferences.getInt("color", mCurrentColor);
mShowCount.setBackgroundColor(mCurrentColor);
} else { ... }To clear all the values in the shared preferences file, call the clear() method on the shared preferences editor and apply the changes.
SharedPreferences.Editor preferencesEditor = mPreferences.edit();
preferencesEditor.putInt("number", 42);
preferencesEditor.clear();
preferencesEditor.apply();public class SettingsActivity extends PreferenceActivity
implements OnSharedPreferenceChangeListener {
public static final String KEY_PREF_SYNC_CONN =
"pref_syncConnectionType";
// ...
public void onSharedPreferenceChanged(
SharedPreferences sharedPreferences,
String key) {
if (key.equals(KEY_PREF_SYNC_CONN)) {
Preference connectionPref = findPreference(key);
// Set summary to be the user-description for
// the selected value
connectionPref.setSummary(
sharedPreferences.getString(key, ""));
}
}
}For proper lifecycle management in the activity, register and unregister your SharedPreferences.OnSharedPreferenceChangeListener during the onResume() and onPause() callbacks, respectively:
@Override
protected void onResume() {
super.onResume();
getPreferenceScreen().getSharedPreferences()
.registerOnSharedPreferenceChangeListener(this);
}
@Override
protected void onPause() {
super.onPause();
getPreferenceScreen().getSharedPreferences()
.unregisterOnSharedPreferenceChangeListener(this);
}When you call registerOnSharedPreferenceChangeListener(), the preference manager does not currently store a reference to the listener. You must hold onto a reference to the listener, or it will be susceptible to garbage collection. Keep a reference to the listener as a class member variable in an object such as an activity that will exist as long as you need the listener.
SharedPreferences.OnSharedPreferenceChangeListener listener =
new SharedPreferences.OnSharedPreferenceChangeListener() {
public void onSharedPreferenceChanged(
SharedPreferences prefs, String key) {
// listener implementation
}
};
prefs.registerOnSharedPreferenceChangeListener(listener);