开始
其实非常有趣，我们经常在开发中使用 SharePrefrence 保存一些轻量级数据，比如判断是否是首次启动，首次启动进入引导页，否则直接到主页面，或者是其它的一些应用场景。
而我们也耳熟能详这样的写法。
根据 Context 获取 SharedPreferences 对象
利用 edit() 方法获取 Editor 对象。
通过 Editor 对象存储 key-value 键值对数据。
通过 commit() 方法提交数据。
public class SplashActivity extends AppCompatActivity { public static final String SP_KEY = "com.zxedu.myapplication.SplashActivity_SP_KEY"; public static final String IS_FIRST_IN = "com.zxedu.myapplication.SplashActivity_IS_FIRST_IN"; @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // 一些业务代码
......
SharedPreferences preferences = getSharedPreferences("name",MODE_PRIVATE); if (preferences.getBoolean(IS_FIRST_IN,true)){ // 跳转引导页面
startActivity(new Intent(this,GuideActivity.class));
finish();
}else{ // 跳转主页面
startActivity(new Intent(this,MainActivity.class));
}
}
}public class GuideActivity extends AppCompatActivity { @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
getSharedPreferences(SplashActivity.SP_KEY,MODE_PRIVATE).edit().putBoolean(SplashActivity.IS_FIRST_IN,false).apply();
}
}从代码中可以看到，一阵混乱操作，没啥特别的地方，但早期开发的人员应该知道，之前我们都是比较青睐 commit() 进行提交的。而现在 Android Studio 在我们使用 commit() 直接提交的时候会直接报黄色警告。
commit() 和 apply() 到底有什么异同？
先说说相同点：
二者都是提交 Prefrence 修改数据；
二者都是原子过程。
不同点直接上源码吧，先看看 commit() 方法的定义：
/**
* Commit your preferences changes back from this Editor to the
* {@link SharedPreferences} object it is editing. This atomically
* performs the requested modifications, replacing whatever is currently
* in the SharedPreferences.
*
* <p>Note that when two editors are modifying preferences at the same
* time, the last one to call commit wins.
*
* <p>If you don't care about the return value and you're
* using this from your application's main thread, consider
* using {@link #apply} instead.
*
* @return Returns true if the new values were successfully written
* to persistent storage.
*/
boolean commit();综合一下 commit() 方法的注释也就是两点：
会返回执行结果。
如果不考虑结果并且是在主线程执行可以考虑
apply()。
再看看 apply() 方法的定义：
/**
* Commit your preferences changes back from this Editor to the
* {@link SharedPreferences} object it is editing. This atomically
* performs the requested modifications, replacing whatever is currently
* in the SharedPreferences.
*
* <p>Note that when two editors are modifying preferences at the same
* time, the last one to call apply wins.
*
* <p>Unlike {@link #commit}, which writes its preferences out
* to persistent storage synchronously, {@link #apply}
* commits its changes to the in-memory
* {@link SharedPreferences} immediately but starts an
* asynchronous commit to disk and you won't be notified of
* any failures. If another editor on this
* {@link SharedPreferences} does a regular {@link #commit}
* while a {@link #apply} is still outstanding, the
* {@link #commit} will block until all async commits are
* completed as well as the commit itself.
*
* <p>As {@link SharedPreferences} instances are singletons within
* a process, it's safe to replace any instance of {@link #commit} with
* {@link #apply} if you were already ignoring the return value.
*
* <p>You don't need to worry about Android component
* lifecycles and their interaction with <code>apply()</code>
* writing to disk. The framework makes sure in-flight disk
* writes from <code>apply()</code> complete before switching
* states.
*
* <p class='note'>The SharedPreferences.Editor interface
* isn't expected to be implemented directly. However, if you
* previously did implement it and are now getting errors
* about missing <code>apply()</code>, you can simply call
* {@link #commit} from <code>apply()</code>.
*/
void apply();略微有点长，大概意思就是 apply() 跟 commit() 不一样的地方是，它使用的是异步而不是同步，它会立即将更改提交到内存，然后异步提交到硬盘，并且如果失败将没有任何提示。
总结一下不同点：
commit()是直接同步地提交到硬件磁盘，因此，多个并发的采用commit()做提交的时候，它们会等待正在处理的commit()保存到磁盘后再进行操作，从而降低了效率。而apply()只是原子的提交到内容，后面再调用apply()的函数进行异步操作。翻源码可以发现
apply()返回值为 void，而commit()返回一个 boolean 值代表是否提交成功。apply()方法不会有任何失败的提示。
那到底使用 commit() 还是 apply()？
大多数情况下，我们都是在同一个进程中，这时候的 SharedPrefrence 都是单实例，一般不会出现并发冲突，如果对提交的结果不关心的话，我们非常建议用 apply() ，当然需要确保操作成功且有后续操作的话，还是需要用 commit() 的。
做不完的开源，写不完的矫情。
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