我有一个片段(F1)与这样的公共方法
public void asd() {
if (getActivity() == null) {
Log.d("yes","it is null");
}
}
是的，当我调用它(从活动)，它是空…
FragmentTransaction transaction1 = getSupportFragmentManager().beginTransaction();
F1 f1 = new F1();
transaction1.replace(R.id.upperPart, f1);
transaction1.commit();
f1.asd();
一定是我做错了什么，但我不知道是什么。
当前回答
最好的办法是在onAttach被调用时保持活动引用，并在任何需要的地方使用活动引用。
@Override
public void onAttach(Context context) {
super.onAttach(activity);
mContext = context;
}
@Override
public void onDetach() {
super.onDetach();
mContext = null;
}
其他回答
在onActivityCreated()中调用getActivity()方法
在哪里调用这个函数?如果在Fragment的构造函数中调用它，它将返回null。
当onCreateView()方法被执行时，只需调用getActivity()。
在commit()之后调用回调函数的顺序:
无论你在commit()之后手动调用什么方法 onAttach () onCreateView () onActivityCreated ()
我需要做一些涉及一些视图的工作，所以onAttach()不适合我;它坠毁。所以我移动了我的代码的一部分，设置一些参数在一个方法调用后立即提交()(1.)，然后在onCreateView()(3.)内处理视图的代码的另一部分。
自Android API级别23起，onAttach(Activity Activity)已弃用。你需要使用onAttach(Context Context)。http://developer.android.com/reference/android/app/Fragment.html onAttach (android.app.Activity)
Activity是一个上下文，所以如果你可以简单地检查上下文是否是一个Activity，并在必要时强制转换它。
@Override
public void onAttach(Context context) {
super.onAttach(context);
Activity a;
if (context instanceof Activity){
a=(Activity) context;
}
}
The other answers that suggest keeping a reference to the activity in onAttach are just suggesting a bandaid to the real problem. When getActivity returns null it means that the Fragment is not attached to the Activity. Most commonly this happens when the Activity has gone away due to rotation or the Activity being finished but the Fragment still has some kind of callback listener registered preventing it from being garbage collected. When the listener gets called if you need to do something with the Activity but the Activity is gone there isn't much you can do. In your code you should just check getActivity() != null and if it's not there then don't do anything. If you keep a reference to the Activity that is gone you are preventing the Activity from being garbage collected. Any UI things you might try to do won't be seen by the user. I can imagine some situations where in the callback listener you want to have a Context for something non-UI related, in those cases it probably makes more sense to get the Application context. Note that the only reason that the onAttach trick isn't a big memory leak is because normally after the callback listener executes it won't be needed anymore and can be garbage collected along with the Fragment, all its View's and the Activity context. If you setRetainInstance(true) there is a bigger chance of a memory leak because the Activity field will also be retained but after rotation that could be the previous Activity not the current one.
