转载请注明出处：http://blog.csdn.net/droyon/article/details/35558783
SettingsProvider采用了双缓冲，我们前面说过SettingsProvider中存在SettingsCache缓冲区，那么在Settings.java中还存在另外一个缓冲区，它就是NameValueCache。
NameValueTable用于描述SettingsProvider的数据表，封装了putString方法。
/**
* Common base for tables of name/value settings.
*/
public static class NameValueTable implements BaseColumns {
public static final String NAME = "name";
public static final String VALUE = "value";
protected static boolean putString(ContentResolver resolver, Uri uri,
String name, String value) {
// The database will take care of replacing duplicates.
try {
ContentValues values = new ContentValues();
values.put(NAME, name);
values.put(VALUE, value);
resolver.insert(uri, values);
return true;
} catch (SQLException e) {
Log.w(TAG, "Can't set key " + name + " in " + uri, e);
return false;
}
}
public static Uri getUriFor(Uri uri, String name) {
return Uri.withAppendedPath(uri, name);
}
}2.1、封装了lazyGetProvider，根据uri得到相应的ContentProvider，此处为IContentProvider，binder跨进程数据访问。
2.2、封装了getStringForUser方法。此方法分两部分，首先得到long newValuesVersion = SystemProperties.getLong(mVersionSystemProperty, 0);，首先从本地cache中得到想要的数据，如果本地cache中不存在想要的数据，那么进行第二部分，查询数据库。
2.3，如果newVersion不等于目前的version，说明本地的cache和SettingsProvider中的数据存在不同步，需要清空本地cache，重新加载。
// Our own user's settings data uses a client-side cache
synchronized (this) {
if (mValuesVersion != newValuesVersion) {
if (LOCAL_LOGV || false) {
Log.v(TAG, "invalidate [" + mUri.getLastPathSegment() + "]: current "
+ newValuesVersion + " != cached " + mValuesVersion);
}
mValues.clear();
mValuesVersion = newValuesVersion;
}
if (mValues.containsKey(name)) {
return mValues.get(name); // Could be null, that's OK -- negative caching
}顾名思义 nameValue 的缓冲池。
// Thread-safe.
private static class NameValueCache {
private final String mVersionSystemProperty;
private final Uri mUri;
private static final String[] SELECT_VALUE =
new String[] { Settings.NameValueTable.VALUE };
private static final String NAME_EQ_PLACEHOLDER = "name=?";
// Must synchronize on 'this' to access mValues and mValuesVersion.
private final HashMap<String, String> mValues = new HashMap<String, String>();
private long mValuesVersion = 0;
// Initially null; set lazily and held forever. Synchronized on 'this'.
private IContentProvider mContentProvider = null;
// The method we'll call (or null, to not use) on the provider
// for the fast path of retrieving settings.
private final String mCallGetCommand;
private final String mCallSetCommand;
public NameValueCache(String versionSystemProperty, Uri uri,
String getCommand, String setCommand) {//传入mCallGetCommand以及mCallSetCommand
mVersionSystemProperty = versionSystemProperty;
mUri = uri;
mCallGetCommand = getCommand;
mCallSetCommand = setCommand;
}
private IContentProvider lazyGetProvider(ContentResolver cr) {//IContentProvider的构造方法
IContentProvider cp = null;
synchronized (this) {
cp = mContentProvider;
if (cp == null) {
cp = mContentProvider = cr.acquireProvider(mUri.getAuthority());
}
}
return cp;
}
public boolean putStringForUser(ContentResolver cr, String name, String value,
final int userHandle) {//putStringForUser
try {
Bundle arg = new Bundle();
arg.putString(Settings.NameValueTable.VALUE, value);
arg.putInt(CALL_METHOD_USER_KEY, userHandle);
IContentProvider cp = lazyGetProvider(cr);
cp.call(cr.getPackageName(), mCallSetCommand, name, arg);
} catch (RemoteException e) {
Log.w(TAG, "Can't set key " + name + " in " + mUri, e);
return false;
}
return true;
}
public String getStringForUser(ContentResolver cr, String name, final int userHandle) {
final boolean isSelf = (userHandle == UserHandle.myUserId());
if (isSelf) {
long newValuesVersion = SystemProperties.getLong(mVersionSystemProperty, 0);
// Our own user's settings data uses a client-side cache
synchronized (this) {
if (mValuesVersion != newValuesVersion) {
if (LOCAL_LOGV || false) {
Log.v(TAG, "invalidate [" + mUri.getLastPathSegment() + "]: current "
+ newValuesVersion + " != cached " + mValuesVersion);
}
mValues.clear();
mValuesVersion = newValuesVersion;
}
if (mValues.containsKey(name)) {
return mValues.get(name); // Could be null, that's OK -- negative caching
}
}
} else {
if (LOCAL_LOGV) Log.v(TAG, "get setting for user " + userHandle
+ " by user " + UserHandle.myUserId() + " so skipping cache");
}
IContentProvider cp = lazyGetProvider(cr);
// Try the fast path first, not using query(). If this
// fails (alternate Settings provider that doesn't support
// this interface?) then we fall back to the query/table
// interface.
if (mCallGetCommand != null) {
try {
Bundle args = null;
if (!isSelf) {
args = new Bundle();
args.putInt(CALL_METHOD_USER_KEY, userHandle);
}
Bundle b = cp.call(cr.getPackageName(), mCallGetCommand, name, args);
if (b != null) {
String value = b.getPairValue();
// Don't update our cache for reads of other users' data
if (isSelf) {
synchronized (this) {
mValues.put(name, value);
}
} else {
if (LOCAL_LOGV) Log.i(TAG, "call-query of user " + userHandle
+ " by " + UserHandle.myUserId()
+ " so not updating cache");
}
return value;
}
// If the response Bundle is null, we fall through
// to the query interface below.
} catch (RemoteException e) {
// Not supported by the remote side? Fall through
// to query().
}
}
Cursor c = null;
try {
c = cp.query(cr.getPackageName(), mUri, SELECT_VALUE, NAME_EQ_PLACEHOLDER,
new String[]{name}, null, null);
if (c == null) {
Log.w(TAG, "Can't get key " + name + " from " + mUri);
return null;
}
String value = c.moveToNext() ? c.getString(0) : null;
synchronized (this) {
mValues.put(name, value);
}
if (LOCAL_LOGV) {
Log.v(TAG, "cache miss [" + mUri.getLastPathSegment() + "]: " +
name + " = " + (value == null ? "(null)" : value));
}
return value;
} catch (RemoteException e) {
Log.w(TAG, "Can't get key " + name + " from " + mUri, e);
return null; // Return null, but don't cache it.
} finally {
if (c != null) c.close();
}
}
}SettingsProvider之Settings.System(Secure)内部类,布布扣,bubuko.com
SettingsProvider之Settings.System(Secure)内部类
原文地址：http://blog.csdn.net/droyon/article/details/35558783
