Android面试题-SharedPreferences源码分析

SharedPreferences sp = context.getSharedPreferences(spName,
Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putString(key, (String) object);
editor.commit();

源码分析

@Override
public SharedPreferences getSharedPreferences(String name, int mode) {
SharedPreferencesImpl sp;
synchronized (ContextImpl.class) {
if (sSharedPrefs == null) {
sSharedPrefs = new ArrayMap<String, ArrayMap<String, SharedPreferencesImpl>>();
}
final String packageName = getPackageName();
ArrayMap<String, SharedPreferencesImpl> packagePrefs = sSharedPrefs.get(packageName);
if (packagePrefs == null) {
packagePrefs = new ArrayMap<String, SharedPreferencesImpl>();
sSharedPrefs.put(packageName, packagePrefs);
}
// At least one application in the world actually passes in a null
// name.
This happened to work because when we generated the file name
// we would stringify it to "null.xml".
Nice.
if (mPackageInfo.getApplicationInfo().targetSdkVersion <
Build.VERSION_CODES.KITKAT) {
if (name == null) {
name = "null";
}
}
sp = packagePrefs.get(name);
if (sp == null) {
File prefsFile = getSharedPrefsFile(name);
sp = new SharedPreferencesImpl(prefsFile, mode);
packagePrefs.put(name, sp);
return sp;
}
}
if ((mode & Context.MODE_MULTI_PROCESS) != 0 ||
getApplicationInfo().targetSdkVersion < android.os.Build.VERSION_CODES.HONEYCOMB) {
// If somebody else (some other process) changed the prefs
// file behind our back, we reload it.
This has been the
// historical (if undocumented) behavior.
sp.startReloadIfChangedUnexpectedly();
}
return sp;
}

源码可知

1） sSharedPrefs是一个静态的ArrayMap，表示一个包可以对应有一组SharedPreferences，并且直接映射文件名到SharedpreferencesImpl

sSharedPrefs = new ArrayMap<String, ArrayMap<String, SharedPreferencesImpl>>();

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