当我单击bottomSheet中的按钮时，我的应用停止运行

Question

当我单击按钮时，我的应用程序停止。我创建了一个应用程序，当我单击NavigationView中的菜单时，它将显示一个BottomSheet，然后在ButtomSheet中，有一个按钮应该单击以打开DatePickerDialog。但在此之前，当加载配置文件（MainActivity）时，它将停止我的程序。

从MainActivity到NavigationView到Modal的一切工作……直到我在Profile.java（MainActivity）内将其编码（下面的代码）

btnDateTime = (Button) findViewById(R.id.btnDateTime);
    txtDateTime =(TextView)findViewById(R.id.txtDateTime);

    btnDateTime.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view){
            calendar = Calendar.getInstance();
            int day = calendar.get(Calendar.DAY_OF_MONTH);
            int month =calendar.get(Calendar.MONTH);
            int year =calendar.get(Calendar.YEAR);

            datePickerDialog = new DatePickerDialog(Profile.this, new DatePickerDialog.OnDateSetListener() {
                @Override
                public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                    txtDateTime.setText(dayOfMonth +"/" + (month +1)+"/"+year);
                }
            },year,month,day);
            datePickerDialog.show();
        }
    });

但是当我删除上述代码行时，一切正常。请帮助我，我真的需要你们（大师）

这是我的个人资料（MainActivity.java）

package com.example.khalessi_jb.reminderapplication;
import android.app.DatePickerDialog;
import android.content.ClipData;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.support.annotation.NonNull;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import org.w3c.dom.Text;
import java.util.Calendar;

public class Profile extends AppCompatActivity implements 
NavigationView.OnNavigationItemSelectedListener{

private DrawerLayout mDrawerLlayout;
private ActionBarDrawerToggle mToggle;
TextView txtFullname;
TextView txtDateTime;
Button btnDateTime;

Calendar calendar;
DatePickerDialog datePickerDialog;
int [] images ={R.drawable.work,R.drawable.location,R.drawable.people};
String [] reminder = {"Finish SBTI Report","21st Anniversary","Managerial Meeting"};
String [] dateToFinish ={"November 1, 2018","December 8, 2018","November 2, 2018"};
View view;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_profile);

    btnDateTime = (Button) findViewById(R.id.btnDateTime);
    txtDateTime =(TextView)findViewById(R.id.txtDateTime);

    btnDateTime.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view){
            calendar = Calendar.getInstance();
            int day = calendar.get(Calendar.DAY_OF_MONTH);
            int month =calendar.get(Calendar.MONTH);
            int year =calendar.get(Calendar.YEAR);

            datePickerDialog = new DatePickerDialog(Profile.this, new DatePickerDialog.OnDateSetListener() {
                @Override
                public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                    txtDateTime.setText(dayOfMonth +"/" + (month +1)+"/"+year);
                }
            },year,month,day);
            datePickerDialog.show();
        }
    });


    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);


    mDrawerLlayout = (DrawerLayout)findViewById(R.id.drawerlayout);
    mToggle = new ActionBarDrawerToggle(this,mDrawerLlayout,toolbar,R.string.navigation_drawer_open,R.string.navigation_drawer_close);
    mDrawerLlayout.addDrawerListener(mToggle);
    mToggle.syncState();


    view = this.getWindow().getDecorView();
    view.setBackgroundResource(R.color.colorLoginBackground);


    ListView ListView =(ListView)findViewById(R.id.lvRemindersList);
    CustomAdapter customAdapter = new CustomAdapter();
    ListView.setAdapter(customAdapter);




}
@Override
public void onBackPressed(){
    if(mDrawerLlayout.isDrawerOpen(GravityCompat.START)){
        mDrawerLlayout.closeDrawer(GravityCompat.START);
    }else{
    super.onBackPressed();
    }
}
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {

    switch (item.getItemId()) {

        case R.id.nav_Account:
           getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                   new ModalEvent()).commit();
            break;
        case R.id.nav_eventreminder:
            ModalEvent modalEvent = new ModalEvent();
            modalEvent.show(getSupportFragmentManager(),"Showed");
            break;

        case R.id.nav_reminder:
            break;

        case R.id.nav_appointmentslots:
            break;

        case R.id.nav_logout:

            break;

    }

    mDrawerLlayout.closeDrawer(GravityCompat.START);
  return true;
}


class CustomAdapter extends BaseAdapter{

    @Override
    public int getCount() {
        return images.length;
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
       view = getLayoutInflater().inflate(R.layout.customlistview,null);
       ImageView imageView = (ImageView)view.findViewById(R.id.imageViewer);
       TextView reminders = (TextView)view.findViewById(R.id.txtReminder);
       TextView date = (TextView)view.findViewById(R.id.txtDate);

       imageView.setImageResource(images[position]);
       reminders.setText(reminder[position]);
       date.setText(dateToFinish[position]);
        return view;
    }
}


}

activity_profile.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawerlayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".Profile">




<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/colorPrimary"
        android:elevation="4dp"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"></android.support.v7.widget.Toolbar>


    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"></FrameLayout>

    <ImageView
        android:id="@+id/imPerson"
        android:layout_width="66dp"
        android:layout_height="62dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="10dp"
        android:layout_marginTop="59dp"
        app:srcCompat="@drawable/profile" />

    <TextView
        android:id="@+id/txtFullname"
        android:layout_width="274dp"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/imPerson"
        android:layout_marginStart="6dp"
        android:layout_marginTop="0dp"
        android:layout_toEndOf="@+id/imPerson"
        android:text="John Bryan Cantiveros"
        android:textColor="@color/white"
        android:textSize="20dp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/txtDesignation"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/txtFullname"
        android:layout_alignStart="@+id/txtFullname"
        android:layout_marginStart="1dp"
        android:layout_marginTop="1dp"
        android:text="Programmer"
        android:textColor="@color/white" />

    <TextView
        android:id="@+id/txtBranch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/txtDesignation"
        android:layout_alignStart="@+id/txtFullname"
        android:layout_marginStart="1dp"
        android:layout_marginTop="0dp"
        android:text="Lagao DJ Interprises"
        android:textColor="@color/white" />

    <View
        android:layout_width="wrap_content"
        android:layout_height="7dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true"
        android:layout_marginStart="10dp"
        android:layout_marginLeft="80dp"
        android:layout_marginTop="130dp"
        android:layout_marginEnd="10dp"
        android:layout_marginRight="80dp"
        android:layout_marginBottom="80dp"
        android:background="@color/Yellow" />

    <ListView
        android:id="@+id/lvRemindersList"
        android:layout_width="wrap_content"
        android:layout_height="422dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:layout_marginStart="10dp"
        android:layout_marginTop="135dp"
        android:layout_marginEnd="10dp"
        android:layout_marginBottom="10dp"
        android:background="@color/white" />

</RelativeLayout>

<android.support.design.widget.NavigationView

    android:id="@+id/nav_view"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_alignParentStart="true"
    android:layout_alignParentTop="true"
    android:layout_gravity="start"
    app:headerLayout="@layout/navigation_header"
    app:menu="@menu/navigation_menu"/>


</android.support.v4.widget.DrawerLayout>

我的ModalEvent.java

package com.example.khalessi_jb.reminderapplication;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.design.widget.BottomSheetDialogFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


public class ModalEvent extends BottomSheetDialogFragment {


@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

    View v = inflater.inflate(R.layout.modal_event,container,false);

    return v;

}

}

我的modal_event.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical"
android:padding="16dp">


<TextView
android:id="@+id/textView12"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Event" />

<EditText
android:id="@+id/txtEventName"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/textView12"
android:layout_centerHorizontal="true"
android:ems="10"
android:hint="Event Title"
android:inputType="textLongMessage" />

<EditText
android:id="@+id/txtWhere"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/textView15"
android:layout_alignStart="@+id/textView13"
android:ems="10"
android:hint="Event Location"
android:inputType="textLongMessage" />

<TextView
android:id="@+id/textView13"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/txtEventName"
android:layout_alignStart="@+id/txtEventName"
android:layout_marginTop="-1dp"
android:text="When" />

<EditText
android:id="@+id/txtDateTime"
android:layout_width="148dp"
android:layout_height="wrap_content"
android:layout_below="@+id/textView13"
android:layout_alignStart="@+id/textView12"
android:layout_marginStart="205dp"
android:layout_marginTop="0dp"
android:ems="10"
android:hint="Date/Time"
android:inputType="time"
android:textSize="15dp" />



<TextView
android:id="@+id/textView15"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textView10"
android:layout_alignStart="@+id/textView13"
android:layout_marginStart="4dp"
android:text="Where" />

<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@+id/textView12"
android:layout_alignParentEnd="true"
android:layout_marginTop="216dp"
android:layout_marginEnd="132dp"
android:text="Create" />

<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="@+id/button"
android:layout_alignParentEnd="true"
android:layout_marginTop="-1dp"
android:layout_marginEnd="15dp"
android:text="Close" />

<TextView
android:id="@+id/textView10"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="@+id/txtDateTime"
android:layout_alignParentStart="true"
android:layout_marginStart="0dp"
android:layout_marginEnd="21dp"
android:layout_toStartOf="@+id/txtDateTime"
android:text="at" />

<TextView
android:id="@+id/textView14"
android:layout_width="124dp"
android:layout_height="wrap_content"
android:layout_alignStart="@+id/button"
android:layout_alignParentTop="true"
android:layout_marginStart="96dp"
android:layout_marginTop="378dp" />

<Button
android:id="@+id/btnDateTime"
android:layout_width="180dp"
android:layout_height="wrap_content"
android:layout_below="@+id/textView13"
android:layout_alignParentStart="true"
android:layout_marginStart="-4dp"
android:text="Choose Date/Time" />

</RelativeLayout>

logcat

2018-11-06 20:32:19.439 20721- 
20721/com.example.khalessi_jb.reminderapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.khalessi_jb.reminderapplication, PID: 20721
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.khalessi_jb.reminderapplication/com.example.khalessi_jb.reminderapplication.Profile}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2724)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527)
    at android.os.Handler.dispatchMessage(Handler.java:110)
    at android.os.Looper.loop(Looper.java:203)
    at android.app.ActivityThread.main(ActivityThread.java:6259)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.khalessi_jb.reminderapplication.Profile.onCreate(Profile.java:55)
    at android.app.Activity.performCreate(Activity.java:6666)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2677)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2789) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1527) 
    at android.os.Handler.dispatchMessage(Handler.java:110) 
    at android.os.Looper.loop(Looper.java:203) 
    at android.app.ActivityThread.main(ActivityThread.java:6259) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924) 

Answer 1

您需要从正在加载的XML中找到按钮

View v = inflater.inflate(R.layout.modal_event,container,false);
Button  btnDateTime = (Button) findViewById(...);
btnDateTime.setOnClick...
return v;