java - 应用程序在尝试打开第二个布局时已停止

Question

我正在创建一个用于安排时间的应用程序，当我选择一个日期并按选择移动到另一个布局以为此日期创建任务时，该应用程序会停止。

这是我的主要内容:

public class CalendarActivity extends AppCompatActivity {

CalendarView calendarView;
TextView dateSelected;
Button selectButton;
Intent scheduleActivityIntent;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_calendar);

    selectButton = (Button) findViewById(R.id.selectButton);
    selectButton.setOnClickListener(new CalendarView.OnClickListener(){

        public void onClick(View v) {
            System.out.println("Button Clicked");

            //scheduleActivityIntent = new Intent(getApplicationContext(), ScheduleActivity.class);
            //startActivity(scheduleActivityIntent);
            startActivity(new Intent(CalendarActivity.this, ScheduleActivity.class));
        }
    });


    calendarView = (CalendarView) findViewById(R.id.calendarView);
    dateSelected = (TextView) findViewById(R.id.dateSelected);
    calendarView.setOnDateChangeListener(new CalendarView.OnDateChangeListener() {
        @Override
        public void onSelectedDayChange(@androidx.annotation.NonNull CalendarView view, int year, int 
month, int dayOfMonth) {
            String date = dayOfMonth + "/" + (month+1) + "/" + year;
            dateSelected.setText(date);
        }
    });

 }
}

这是我的第二个 Activity ，它应该是任务 ListView :

public class ScheduleActivity extends CalendarActivity {

private static final String TAG = "ScheduleActivity";

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_schedule);

    Log.d(TAG, "onCreate: Started");
    ListView taskList = (ListView) findViewById(R.id.schedule);

    //Create object insert
    Task haircut = new Task("Haircut", "21/01/2020", "14:00", 1, 2, "Go get a haircut");
    Task work = new Task("Work", "21/01/2020", "18:00", 6, 3, "Might be closing");

    //Should be made as a function in order to insert user's tasks

    //Creating Array adapter
    ArrayList<Task> taskListAdapter = new ArrayList<>();
    taskListAdapter.add(haircut);
    taskListAdapter.add(work);

    ScheduleAdapter adapter = new ScheduleAdapter(ScheduleActivity.this, R.layout.schedule_items, taskListAdapter);

    taskList.setAdapter(adapter);
}

}

这是适配器:

public class ScheduleAdapter extends ArrayAdapter <Task>
{
private static final String TAG = "ScheduleAdapter";
private Context mContext;
int mResource;

//Default constructor for the adapter

public ScheduleAdapter(@NonNull Context context, int resource, @NonNull ArrayList<Task> objects) {
    super(context, resource, objects);
    this.mContext = mContext;
    this.mResource = resource;
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    //get the task info

    String name = getItem(position).getTaskName();
    String date = getItem(position).getTaskDate();
    String time = getItem(position).getTaskTime();
    int timeFinish = getItem(position).getTaskTimeFinish();
    int urgency = getItem(position).getTaskUrgency();
    String description = getItem(position).getTaskDescription();

    //create the task object with the info
    Task aTask = new Task(name, date, time, timeFinish, urgency, description);

    LayoutInflater inflater = LayoutInflater.from(mContext);
    convertView = inflater.inflate(mResource, parent, false);

    TextView tvName = (TextView) convertView.findViewById(R.id.task_name);
    TextView tvTime = (TextView) convertView.findViewById(R.id.task_time);
    TextView tvUrgency = (TextView) convertView.findViewById(R.id.task_urgency);

    tvName.setText(name);
    tvTime.setText(time);
    tvUrgency.setText(urgency);

    return convertView;
}

}

从 Logcat 看来，它崩溃的原因是:

2020-02-04 13:19:51.621 5841-5841/com.example.calendarview E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.calendarview, PID: 5841
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
    at android.view.LayoutInflater.from(LayoutInflater.java:232)
    at com.example.calendarview.ScheduleAdapter.getView(ScheduleAdapter.java:44)
    at android.widget.AbsListView.obtainView(AbsListView.java:2362)
    at android.widget.ListView.makeAndAddView(ListView.java:1970)
    at android.widget.ListView.fillDown(ListView.java:704)
    at android.widget.ListView.fillFromTop(ListView.java:765)
    at android.widget.ListView.layoutChildren(ListView.java:1744)
    at android.widget.AbsListView.onLayout(AbsListView.java:2161)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1741)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1585)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1494)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:724)
    at android.view.View.layout(View.java:17523)
    at android.view.ViewGroup.layout(ViewGroup.java:5612)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2342)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2069)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1246)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6301)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:871)
    at android.view.Choreographer.doCallbacks(Choreographer.java:683)
    at android.view.Choreographer.doFrame(Choreographer.java:619)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:857)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6077)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

但是我找不到在哪里

Answer 1

您正在 LayoutInflater.from(mContext) 中传递空上下文:

在您的 ScheduleAdapter 构造函数中进行更改

this.mContext = mContext;

至

this.mContext = context;