Question

我在主要活动中有一个片段来处理我活动的所有操作。

当我使用片段属性时，很少发生NullPointerException：

片段代码：

    public class ProjectInfoFragment extends Fragment {
        private static final String ARG_PID = "pid";
        private int projectId;
        View view;
        public ProjectInfoFragment() {
            // Required empty public constructor
        }

        public static ProjectInfoFragment newInstance(int pid) {
            ProjectInfoFragment fragment = new ProjectInfoFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_PID, pid);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            if (getArguments() != null) {
                projectId = getArguments().getInt(ARG_PID);
            }
        }

        @Override
        public void onResume() {
            super.onResume();
            mainAction();
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup  container, Bundle savedInstanceState) {
            view = inflater.inflate(R.layout.fragment_project_info, container, false);
            return view;
        }

        private void mainAction() {
            ProjectModel projectModel = new ProjectModel(getContext());
            if (!projectModel.findByKey(projectId + "")) { //// line 121
            //!!!!!!! here NullPointerException occurs !!!!!!
                return;
            }
        }   

    }

重要提示：我在mainAction（）中做了很多事情，必须在onResume（）中完成，我不能在createView或其他函数中执行此操作。

日志：

    java.lang.NullPointerException: Attempt to invoke virtual method boolean ir.rabint.shahta.model.ProjectModel.findByKey(java.lang.String) on a null object referencen
    at ir.rabint.shahta.activity.fragment.ProjectInfoFragment.mainAction(ProjectInfoFragment.java:121)
    at ir.rabint.shahta.activity.fragment.ProjectInfoFragment.onResume(ProjectInfoFragment.java:92)
    at android.support.v4.app.Fragment.performResume(Fragment.java:2238)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1346)
    at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1528)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1595)
    at android.support.v4.app.BackStackRecord.uteOps(BackStackRecord.java:758)
    at android.support.v4.app.FragmentManagerImpl.uteOps(FragmentManager.java:2363)
    at android.support.v4.app.FragmentManagerImpl.uteOpsTogether(FragmentManager.java:2149)
    at android.support.v4.app.FragmentManagerImpl.optimizeAnduteOps(FragmentManager.java:2103)
    at android.support.v4.app.FragmentManagerImpl.PendingActions(FragmentManager.java:2013)
    at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710)
    at android.os.Handler.handleCallback(Handler.java:836)
    at android.os.Handler.dispatchMessage(Handler.java:103)
    at android.os.Looper.loop(Looper.java:203)
    at android.app.ActivityThread.main(ActivityThread.java:6247)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)

Answer 1

!运算符仅适用于Boolean数据类型/方法。在这里，您将比较堆栈跟踪中所述的String。以下是

if(projectModel != null){
    if(!projectModel.findByKey(projectId + "").equals("")){
    return;
    }
}else{
//do whatever you want
}

片段的onResume中的NullPointerException

1 个答案: