碰到一个很难复现的crash，LogCat捕捉到如下crash信息：

android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment MyFragment: make sure class name exists, is public, and has an empty constructor that is public

从Fragment文档中看到可能与此crash相关的说明： 译：所有Fragment子类必须要包含无参数构造器。Framework在必要时候常常需要重新实例化一个fragment，尤其在恢复fragment状态时，需要能找到这个构造器。如果找不到，在上述提到的情况下就会抛出运行时异常。

原文：All subclasses of Fragment must include a public no-argument constructor. The framework will often re-instantiate a fragment class when needed, in particular during state restore, and needs to be able to find this constructor to instantiate it. If the no-argument constructor is not available, a runtime exception will occur in some cases during state restore.

因为我偏向于使用如下方法实例化Fragment，所以代码中就没再定义构造器：

public static MyFragment newInstance(Date date) {
    Log.d(TAG, "newInstance");
    Bundle args = new Bundle();
    args.putLong(EXTRA_DATE, date.getTime());

    MyFragment fragment = new MyFragment();
    fragment.setArguments(args);
    return fragment;
}

为了解决crash，以及保险起见，就添加了一个空的构造器：

public MyFragment() {
    super();
}

因为crash很难复现，所以并不能确定是否有用。

参考： Fragment Class Overview Android InstantiationException With Fragment (It Is Public)