Android的SharedPreferences接口是在哪里实现的

转载自：https://blog.csdn.net/wxyyxc1992/article/details/17222841

他的博客是2013年的，我又去android27的源码里面找ContextImpl.java

连续按2次shift就能查找到了，记住是android-27androidapp的那个，不是rt.jarcomsuncorbaseimplcorba的那个

也可以sdk目录下查找

我的SDK目录C:UserslcyAppDataLocalAndroidSdksourcesandroid-27androidapp

    SharedPreferences 不过是个接口，它定义了一些操作xml文件的方法，其真正实现类为SharedPreferencesImpl ，该类之前是ContextIml的内部类，但是现在单独出来了，仍然在sdk目录下。该类如下：

final class SharedPreferencesImpl implements SharedPreferences {
    ......
    @Nullable
    public String getString(String key, @Nullable String defValue) {/通过key值获取对应的value值
        synchronized (mLock) {
            awaitLoadedLocked();
            String v = (String)mMap.get(key);
            return v != null ? v : defValue;
        }
    }

    @Nullable
    public Set<String> getStringSet(String key, @Nullable Set<String> defValues) {
        synchronized (mLock) {
            awaitLoadedLocked();
            Set<String> v = (Set<String>) mMap.get(key);
            return v != null ? v : defValues;
        }
    }
    ......
    public final class EditorImpl implements Editor {//获得该SharedPreferencesImpl对象对应的Edito类，对数据进行操作
        private final Object mLock = new Object();


        @GuardedBy("mLock")
        private final Map<String, Object> mModified = Maps.newHashMap();
        ...
    }
}

    getSharedPreferences()方法本身是Context这个接口中定义的一个抽象方法，由ContextImpl类负责实现。调用getSharedPreferences()获取对应的的文件，该函数实现功能如下：

class ContextImpl extends Context {
    ......
    @Override
    public SharedPreferences getSharedPreferences(String name, int mode) {
        // 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";
            }
        }

        File file;
        synchronized (ContextImpl.class) {
            if (mSharedPrefsPaths == null) {
                mSharedPrefsPaths = new ArrayMap<>();
            }
            file = mSharedPrefsPaths.get(name);
            if (file == null) {
                file = getSharedPreferencesPath(name);
                mSharedPrefsPaths.put(name, file);
            }
        }
        return getSharedPreferences(file, mode);
    }

    @Override
    public SharedPreferences getSharedPreferences(File file, int mode) {
        SharedPreferencesImpl sp;
        synchronized (ContextImpl.class) {
            final ArrayMap<File, SharedPreferencesImpl> cache = getSharedPreferencesCacheLocked();
            sp = cache.get(file);
            if (sp == null) {
                checkMode(mode);
                if (getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.O) {
                    if (isCredentialProtectedStorage()
                            && !getSystemService(UserManager.class)
                                    .isUserUnlockingOrUnlocked(UserHandle.myUserId())) {
                        throw new IllegalStateException("SharedPreferences in credential encrypted "
                                + "storage are not available until after user is unlocked");
                    }
                }
                sp = new SharedPreferencesImpl(file, mode);
                cache.put(file, sp);
                return sp;
            }
        }
        if ((mode & Context.MODE_MULTI_PROCESS) != 0 ||
            getApplicationInfo().targetSdkVersion < 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;
    }
    ......
}

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