我是java初学者。现在我正在学习android开发，对android.view.ContextThemeWrapper的类定义感到困惑。它是android.content.ContextWrapper的子类。这两个类都包含一个字段 mBase（和 android.content.Context 的实例）。在基类中，它声明时没有访问修饰符，但在子类中，它声明时使用私有修饰符。
所以 android.view.ContextThemeWrapper 的一个实例确实有两个名为“mBase”的字段，只有在派生部分中定义的那个是可见的，而在基类部分中声明的那个是隐藏的。为什么在这里派生类的实例中需要两个“mBase”字段的副本？在哪种情况下，我应该将基类中定义的字段覆盖为私有字段？
我需要你的帮助。提前致谢。
下面是这两个类的定义：
android.content.ContextWrapper：
/**
* Proxying implementation of Context that simply delegates all of its calls to
* another Context. Can be subclassed to modify behavior without changing
* the original Context.
*/
public class ContextWrapper extends Context {
Context mBase;
public ContextWrapper(Context base) {
mBase = base;
}
/**
* Set the base context for this ContextWrapper. All calls will then be
* delegated to the base context. Throws
* IllegalStateException if a base context has already been set.
*
* @param base The new base context for this wrapper.
*/
protected void attachBaseContext(Context base) {
if (mBase != null) {
throw new IllegalStateException("Base context already set");
}
mBase = base;
}
/**
* @return the base context as set by the constructor or setBaseContext
*/
public Context getBaseContext() {
return mBase;
}
@Override
public AssetManager getAssets() {
return mBase.getAssets();
}
@Override
public Resources getResources()
{
return mBase.getResources();
}
@Override
public PackageManager getPackageManager() {
return mBase.getPackageManager();
}
@Override
public ContentResolver getContentResolver() {
return mBase.getContentResolver();
}
@Override
public Looper getMainLooper() {
return mBase.getMainLooper();
}
@Override
public Context getApplicationContext() {
return mBase.getApplicationContext();
}
@Override
public void setTheme(int resid) {
mBase.setTheme(resid);
}
/** @hide */
@Override
public int getThemeResId() {
return mBase.getThemeResId();
}
@Override
public Resources.Theme getTheme() {
return mBase.getTheme();
}
@Override
public ClassLoader getClassLoader() {
return mBase.getClassLoader();
}
@Override
public String getPackageName() {
return mBase.getPackageName();
}
@Override
public ApplicationInfo getApplicationInfo() {
return mBase.getApplicationInfo();
}
@Override
public String getPackageResourcePath() {
return mBase.getPackageResourcePath();
}
@Override
public String getPackageCodePath() {
return mBase.getPackageCodePath();
}
/** @hide */
@Override
public File getSharedPrefsFile(String name) {
return mBase.getSharedPrefsFile(name);
}
@Override
public SharedPreferences getSharedPreferences(String name, int mode) {
return mBase.getSharedPreferences(name, mode);
}
@Override
public FileInputStream openFileInput(String name)
throws FileNotFoundException {
return mBase.openFileInput(name);
}
@Override
public FileOutputStream openFileOutput(String name, int mode)
throws FileNotFoundException {
return mBase.openFileOutput(name, mode);
}
@Override
public boolean deleteFile(String name) {
return mBase.deleteFile(name);
}
@Override
public File getFileStreamPath(String name) {
return mBase.getFileStreamPath(name);
}
@Override
public String[] fileList() {
return mBase.fileList();
}
@Override
public File getFilesDir() {
return mBase.getFilesDir();
}
@Override
public File getExternalFilesDir(String type) {
return mBase.getExternalFilesDir(type);
}
@Override
public File getObbDir() {
return mBase.getObbDir();
}
@Override
public File getCacheDir() {
return mBase.getCacheDir();
}
@Override
public File getExternalCacheDir() {
return mBase.getExternalCacheDir();
}
@Override
public File getDir(String name, int mode) {
return mBase.getDir(name, mode);
}
@Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, CursorFactory factory) {
return mBase.openOrCreateDatabase(name, mode, factory);
}
@Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, CursorFactory factory,
DatabaseErrorHandler errorHandler) {
return mBase.openOrCreateDatabase(name, mode, factory, errorHandler);
}
@Override
public boolean deleteDatabase(String name) {
return mBase.deleteDatabase(name);
}
@Override
public File getDatabasePath(String name) {
return mBase.getDatabasePath(name);
}
@Override
public String[] databaseList() {
return mBase.databaseList();
}
@Override
public Drawable getWallpaper() {
return mBase.getWallpaper();
}
@Override
public Drawable peekWallpaper() {
return mBase.peekWallpaper();
}
@Override
public int getWallpaperDesiredMinimumWidth() {
return mBase.getWallpaperDesiredMinimumWidth();
}
@Override
public int getWallpaperDesiredMinimumHeight() {
return mBase.getWallpaperDesiredMinimumHeight();
}
@Override
public void setWallpaper(Bitmap bitmap) throws IOException {
mBase.setWallpaper(bitmap);
}
@Override
public void setWallpaper(InputStream data) throws IOException {
mBase.setWallpaper(data);
}
@Override
public void clearWallpaper() throws IOException {
mBase.clearWallpaper();
}
@Override
public void startActivity(Intent intent) {
mBase.startActivity(intent);
}
/** @hide */
@Override
public void startActivityAsUser(Intent intent, UserHandle user) {
mBase.startActivityAsUser(intent, user);
}
@Override
public void startActivity(Intent intent, Bundle options) {
mBase.startActivity(intent, options);
}
/** @hide */
@Override
public void startActivityAsUser(Intent intent, Bundle options, UserHandle user) {
mBase.startActivityAsUser(intent, options, user);
}
@Override
public void startActivities(Intent[] intents) {
mBase.startActivities(intents);
}
@Override
public void startActivities(Intent[] intents, Bundle options) {
mBase.startActivities(intents, options);
}
/** @hide */
@Override
public void startActivitiesAsUser(Intent[] intents, Bundle options, UserHandle userHandle) {
mBase.startActivitiesAsUser(intents, options, userHandle);
}
@Override
public void startIntentSender(IntentSender intent,
Intent fillInIntent, int flagsMask, int flagsValues, int extraFlags)
throws IntentSender.SendIntentException {
mBase.startIntentSender(intent, fillInIntent, flagsMask,
flagsValues, extraFlags);
}
@Override
public void startIntentSender(IntentSender intent,
Intent fillInIntent, int flagsMask, int flagsValues, int extraFlags,
Bundle options) throws IntentSender.SendIntentException {
mBase.startIntentSender(intent, fillInIntent, flagsMask,
flagsValues, extraFlags, options);
}
@Override
public void sendBroadcast(Intent intent) {
mBase.sendBroadcast(intent);
}
@Override
public void sendBroadcast(Intent intent, String receiverPermission) {
mBase.sendBroadcast(intent, receiverPermission);
}
@Override
public void sendOrderedBroadcast(Intent intent,
String receiverPermission) {
mBase.sendOrderedBroadcast(intent, receiverPermission);
}
@Override
public void sendOrderedBroadcast(
Intent intent, String receiverPermission, BroadcastReceiver resultReceiver,
Handler scheduler, int initialCode, String initialData,
Bundle initialExtras) {
mBase.sendOrderedBroadcast(intent, receiverPermission,
resultReceiver, scheduler, initialCode,
initialData, initialExtras);
}
@Override
public void sendBroadcastAsUser(Intent intent, UserHandle user) {
mBase.sendBroadcastAsUser(intent, user);
}
@Override
public void sendBroadcastAsUser(Intent intent, UserHandle user,
String receiverPermission) {
mBase.sendBroadcastAsUser(intent, user, receiverPermission);
}
@Override
public void sendOrderedBroadcastAsUser(Intent intent, UserHandle user,
String receiverPermission, BroadcastReceiver resultReceiver, Handler scheduler,
int initialCode, String initialData, Bundle initialExtras) {
mBase.sendOrderedBroadcastAsUser(intent, user, receiverPermission, resultReceiver,
scheduler, initialCode, initialData, initialExtras);
}
@Override
public void sendStickyBroadcast(Intent intent) {
mBase.sendStickyBroadcast(intent);
}
@Override
public void sendStickyOrderedBroadcast(
Intent intent, BroadcastReceiver resultReceiver,
Handler scheduler, int initialCode, String initialData,
Bundle initialExtras) {
mBase.sendStickyOrderedBroadcast(intent,
resultReceiver, scheduler, initialCode,
initialData, initialExtras);
}
@Override
public void removeStickyBroadcast(Intent intent) {
mBase.removeStickyBroadcast(intent);
}
@Override
public void sendStickyBroadcastAsUser(Intent intent, UserHandle user) {
mBase.sendStickyBroadcastAsUser(intent, user);
}
@Override
public void sendStickyOrderedBroadcastAsUser(Intent intent,
UserHandle user, BroadcastReceiver resultReceiver,
Handler scheduler, int initialCode, String initialData,
Bundle initialExtras) {
mBase.sendStickyOrderedBroadcastAsUser(intent, user, resultReceiver,
scheduler, initialCode, initialData, initialExtras);
}
@Override
public void removeStickyBroadcastAsUser(Intent intent, UserHandle user) {
mBase.removeStickyBroadcastAsUser(intent, user);
}
@Override
public Intent registerReceiver(
BroadcastReceiver receiver, IntentFilter filter) {
return mBase.registerReceiver(receiver, filter);
}
@Override
public Intent registerReceiver(
BroadcastReceiver receiver, IntentFilter filter,
String broadcastPermission, Handler scheduler) {
return mBase.registerReceiver(receiver, filter, broadcastPermission,
scheduler);
}
/** @hide */
@Override
public Intent registerReceiverAsUser(
BroadcastReceiver receiver, UserHandle user, IntentFilter filter,
String broadcastPermission, Handler scheduler) {
return mBase.registerReceiverAsUser(receiver, user, filter, broadcastPermission,
scheduler);
}
@Override
public void unregisterReceiver(BroadcastReceiver receiver) {
mBase.unregisterReceiver(receiver);
}
@Override
public ComponentName startService(Intent service) {
return mBase.startService(service);
}
@Override
public boolean stopService(Intent name) {
return mBase.stopService(name);
}
/** @hide */
@Override
public ComponentName startServiceAsUser(Intent service, UserHandle user) {
return mBase.startServiceAsUser(service, user);
}
/** @hide */
@Override
public boolean stopServiceAsUser(Intent name, UserHandle user) {
return mBase.stopServiceAsUser(name, user);
}
@Override
public boolean bindService(Intent service, ServiceConnection conn,
int flags) {
return mBase.bindService(service, conn, flags);
}
/** @hide */
@Override
public boolean bindService(Intent service, ServiceConnection conn, int flags, int userHandle) {
return mBase.bindService(service, conn, flags, userHandle);
}
@Override
public void unbindService(ServiceConnection conn) {
mBase.unbindService(conn);
}
@Override
public boolean startInstrumentation(ComponentName className,
String profileFile, Bundle arguments) {
return mBase.startInstrumentation(className, profileFile, arguments);
}
@Override
public Object getSystemService(String name) {
return mBase.getSystemService(name);
}
@Override
public int checkPermission(String permission, int pid, int uid) {
return mBase.checkPermission(permission, pid, uid);
}
@Override
public int checkCallingPermission(String permission) {
return mBase.checkCallingPermission(permission);
}
@Override
public int checkCallingOrSelfPermission(String permission) {
return mBase.checkCallingOrSelfPermission(permission);
}
@Override
public void enforcePermission(
String permission, int pid, int uid, String message) {
mBase.enforcePermission(permission, pid, uid, message);
}
@Override
public void enforceCallingPermission(String permission, String message) {
mBase.enforceCallingPermission(permission, message);
}
@Override
public void enforceCallingOrSelfPermission(
String permission, String message) {
mBase.enforceCallingOrSelfPermission(permission, message);
}
@Override
public void grantUriPermission(String toPackage, Uri uri, int modeFlags) {
mBase.grantUriPermission(toPackage, uri, modeFlags);
}
@Override
public void revokeUriPermission(Uri uri, int modeFlags) {
mBase.revokeUriPermission(uri, modeFlags);
}
@Override
public int checkUriPermission(Uri uri, int pid, int uid, int modeFlags) {
return mBase.checkUriPermission(uri, pid, uid, modeFlags);
}
@Override
public int checkCallingUriPermission(Uri uri, int modeFlags) {
return mBase.checkCallingUriPermission(uri, modeFlags);
}
@Override
public int checkCallingOrSelfUriPermission(Uri uri, int modeFlags) {
return mBase.checkCallingOrSelfUriPermission(uri, modeFlags);
}
@Override
public int checkUriPermission(Uri uri, String readPermission,
String writePermission, int pid, int uid, int modeFlags) {
return mBase.checkUriPermission(uri, readPermission, writePermission,
pid, uid, modeFlags);
}
@Override
public void enforceUriPermission(
Uri uri, int pid, int uid, int modeFlags, String message) {
mBase.enforceUriPermission(uri, pid, uid, modeFlags, message);
}
@Override
public void enforceCallingUriPermission(
Uri uri, int modeFlags, String message) {
mBase.enforceCallingUriPermission(uri, modeFlags, message);
}
@Override
public void enforceCallingOrSelfUriPermission(
Uri uri, int modeFlags, String message) {
mBase.enforceCallingOrSelfUriPermission(uri, modeFlags, message);
}
@Override
public void enforceUriPermission(
Uri uri, String readPermission, String writePermission,
int pid, int uid, int modeFlags, String message) {
mBase.enforceUriPermission(
uri, readPermission, writePermission, pid, uid, modeFlags,
message);
}
@Override
public Context createPackageContext(String packageName, int flags)
throws PackageManager.NameNotFoundException {
return mBase.createPackageContext(packageName, flags);
}
/** @hide */
@Override
public Context createPackageContextAsUser(String packageName, int flags, UserHandle user)
throws PackageManager.NameNotFoundException {
return mBase.createPackageContextAsUser(packageName, flags, user);
}
@Override
public Context createConfigurationContext(Configuration overrideConfiguration) {
return mBase.createConfigurationContext(overrideConfiguration);
}
@Override
public Context createDisplayContext(Display display) {
return mBase.createDisplayContext(display);
}
@Override
public boolean isRestricted() {
return mBase.isRestricted();
}
/** @hide */
@Override
public CompatibilityInfoHolder getCompatibilityInfo(int displayId) {
return mBase.getCompatibilityInfo(displayId);
}
}
android.view.ContextThemeWrapper：
/**
* A ContextWrapper that allows you to modify the theme from what is in the
* wrapped context.
*/
public class ContextThemeWrapper extends ContextWrapper {
private Context mBase;
private int mThemeResource;
private Resources.Theme mTheme;
private LayoutInflater mInflater;
private Configuration mOverrideConfiguration;
private Resources mResources;
public ContextThemeWrapper() {
super(null);
}
public ContextThemeWrapper(Context base, int themeres) {
super(base);
mBase = base;
mThemeResource = themeres;
}
@Override protected void attachBaseContext(Context newBase) {
super.attachBaseContext(newBase);
mBase = newBase;
}
/**
* Call to set an "override configuration" on this context -- this is
* a configuration that replies one or more values of the standard
* configuration that is applied to the context. See
* {@link Context#createConfigurationContext(Configuration)} for more
* information.
*
* <p>This method can only be called once, and must be called before any
* calls to {@link #getResources()} are made.
*/
public void applyOverrideConfiguration(Configuration overrideConfiguration) {
if (mResources != null) {
throw new IllegalStateException("getResources() has already been called");
}
if (mOverrideConfiguration != null) {
throw new IllegalStateException("Override configuration has already been set");
}
mOverrideConfiguration = new Configuration(overrideConfiguration);
}
@Override
public Resources getResources() {
if (mResources != null) {
return mResources;
}
if (mOverrideConfiguration == null) {
mResources = super.getResources();
return mResources;
} else {
Context resc = createConfigurationContext(mOverrideConfiguration);
mResources = resc.getResources();
return mResources;
}
}
@Override public void setTheme(int resid) {
mThemeResource = resid;
initializeTheme();
}
/** @hide */
@Override
public int getThemeResId() {
return mThemeResource;
}
@Override public Resources.Theme getTheme() {
if (mTheme != null) {
return mTheme;
}
mThemeResource = Resources.selectDefaultTheme(mThemeResource,
getApplicationInfo().targetSdkVersion);
initializeTheme();
return mTheme;
}
@Override public Object getSystemService(String name) {
if (LAYOUT_INFLATER_SERVICE.equals(name)) {
if (mInflater == null) {
mInflater = LayoutInflater.from(mBase).cloneInContext(this);
}
return mInflater;
}
return mBase.getSystemService(name);
}
/**
* Called by {@link #setTheme} and {@link #getTheme} to apply a theme
* resource to the current Theme object. Can override to change the
* default (simple) behavior. This method will not be called in multiple
* threads simultaneously.
*
* @param theme The Theme object being modified.
* @param resid The theme style resource being applied to <var>theme</var>.
* @param first Set to true if this is the first time a style is being
* applied to <var>theme</var>.
*/
protected void onApplyThemeResource(Resources.Theme theme, int resid, boolean first) {
theme.applyStyle(resid, true);
}
private void initializeTheme() {
final boolean first = mTheme == null;
if (first) {
mTheme = getResources().newTheme();
Resources.Theme theme = mBase.getTheme();
if (theme != null) {
mTheme.setTo(theme);
}
}
onApplyThemeResource(mTheme, mThemeResource, first);
}
}