setUserVisibleHint中的空上下文 [英] Null Context in setUserVisibleHint

问题描述

当ViewPager中的片段变为可见时，需要向用户显示一条消息.当前的呼叫是:

A message needs to be displayed to the user when a fragment in a ViewPager becomes visible. Currently the call is:

// Within a class that extends Fragment
@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);

    if (isVisibleToUser) {
        MessageUtility.displayMessage(getContext());
    }
}

MessageUtility.displayMessage()打开一个带有消息的警报对话框.

MessageUtility.displayMessage() opens an alert dialog with a message.

Context是显示消息所必需的.但是，不能保证在调用setUserVisibleHint()时就附加该片段.因此，即使isVisiableToUser == true，Context也将是null.

Context is required to display the message. However, the fragment is not guaranteed to be attached by the time setUserVisibleHint() is called. Thus, the Context will be null, even though isVisiableToUser == true .

从理论上讲，检查isVisibleToUser && isAttached()是可行的，但是isAttached() == true之后不会引发setUserVisibleHint().

Checking isVisibleToUser && isAttached() works in theory, but setUserVisibleHint() is not provoked after isAttached() == true.

是否有某种方法可以允许对displayMessage()的呼叫等待，直到连接Fragment为止?

Is there some way to allow the call to displayMessage() to wait until the Fragment is attached?

推荐答案

迟到总比没有好，我有一点棘手的解决方案，请从onActivityCreated()方法调用setUserVisibleHint().

Better late than never ,I have a little hackish solution ,call setUserVisibleHint() from onActivityCreated() method.

private boolean myIsVisibleToUser;

 @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    myIsVisibleToUser=isVisibleToUser;
    if (isVisibleToUser && getActivity()!=null) {
          MessageUtility.displayMessage(getContext());    
        }
}


@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    setUserVisibleHint(myIsVisibleToUser);

}

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