操作简单，以键值对的方式存储在本地。
getSharedPreference在子线程进行读取操作，为啥还会阻塞线程呢? 因为get操作要等所有键值对都读取完毕之后，才能进行操作。
看源码：
val sp = getSharedPreferences("zhen", Context.MODE_PRIVATE) val editor = sp.edit() editor.putString("key", "value") editor.commit() val value = sp.getString("key", "null")
SharedPreferenceImpl
SharedPreferencesImpl(File file, int mode) { mFile = file; mBackupFile = makeBackupFile(file); mMode = mode; mLoaded = false; mMap = null; startLoadFromDisk(); }
开启子线程进行文件读取
private void startLoadFromDisk() { synchronized (mLock) { mLoaded = false; } new Thread("SharedPreferencesImpl-load") { public void run() { loadFromDisk(); } }.start(); }
private void loadFromDisk() { synchronized (mLock) { if (mLoaded) { return; } if (mBackupFile.exists()) { mFile.delete(); mBackupFile.renameTo(mFile); } } // Debugging if (mFile.exists() && !mFile.canRead()) { Log.w(TAG, "Attempt to read preferences file " + mFile + " without permission"); } Map map = null; StructStat stat = null; try { stat = Os.stat(mFile.getPath()); if (mFile.canRead()) { BufferedInputStream str = null; try { str = new BufferedInputStream( new FileInputStream(mFile), 16*1024); map = XmlUtils.readMapXml(str); } catch (Exception e) { Log.w(TAG, "Cannot read " + mFile.getAbsolutePath(), e); } finally { IoUtils.closeQuietly(str); } } } catch (ErrnoException e) { /* ignore */ } synchronized (mLock) { mLoaded = true; if (map != null) { mMap = map; mStatTimestamp = stat.st_mtim; mStatSize = stat.st_size; } else { mMap = new HashMap<>(); } mLock.notifyAll(); } }
那为啥在子线程操作，还会阻塞UI呢？
@Nullable public String getString(String key, @Nullable String defValue) { synchronized (mLock) { awaitLoadedLocked(); String v = (String)mMap.get(key); return v != null ? v : defValue; } }//会等待所有的都读取完毕之后，才进行get操作
private void awaitLoadedLocked() { if (!mLoaded) { // Raise an explicit StrictMode onReadFromDisk for this // thread, since the real read will be in a different // thread and otherwise ignored by StrictMode. BlockGuard.getThreadPolicy().onReadFromDisk(); } while (!mLoaded) { try { mLock.wait(); } catch (InterruptedException unused) { } } }
//put操作会使用SharedPreference的内部类EditorImpl, 统一commit。
public Editor putString(String key, @Nullable String value) { synchronized (mLock) { mModified.put(key, value); return this; } }
public boolean commit() { long startTime = 0; if (DEBUG) { startTime = System.currentTimeMillis(); } MemoryCommitResult mcr = commitToMemory(); SharedPreferencesImpl.this.enqueueDiskWrite( mcr, null /* sync write on this thread okay */); try { mcr.writtenToDiskLatch.await(); } catch (InterruptedException e) { return false; } finally { if (DEBUG) { Log.d(TAG, mFile.getName() + ":" + mcr.memoryStateGeneration + " committed after " + (System.currentTimeMillis() - startTime) + " ms"); } } notifyListeners(mcr); return mcr.writeToDiskResult; }