SharedPreferences用法

一、SharedPreferences将数据文件保存在指定路径上

通过反射：

private void initSharedPreferences(String path,String name,int mode) {
    try {
        Field field =ContextWrapper.class.getDeclaredField("mBase");
	field.setAccessible(true);
	Object obj = field.get(this);
	field = obj.getClass().getDeclaredField("mPreferencesDir");
	field.setAccessible(true);
	File file = new File(path);
	field.set(obj, file);
	sharedPreferences = getSharedPreferences(name, mode);
	editor = sharedPreferences.edit();
    } catch (Exception e) {
	e.printStackTrace();
    }
}

原理：

查看getSharedPreferences源码（ContextImpl.java类）

    @Override
    public SharedPreferences getSharedPreferences(String name, int mode) {
        SharedPreferencesImpl sp;
        synchronized (sSharedPrefs) {
            sp = sSharedPrefs.get(name);
            if (sp == null) {
                File prefsFile = getSharedPrefsFile(name);
                sp = new SharedPreferencesImpl(prefsFile, mode);
                sSharedPrefs.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;
    }

public File getSharedPrefsFile(String name) {
    return makeFilename(getPreferencesDir(), name + ".xml");
}

private File getPreferencesDir() {
    synchronized (mSync) {
        if (mPreferencesDir == null) {
             mPreferencesDir = new File(getDataDirFile(), "shared_prefs");
         }
         return mPreferencesDir;
    }
}