cardview按钮单击mainactivity中的Listener，删除给出空指针异常的特定联系人

Question

虽然我能够从sqlite数据库中删除选定的联系人，但当我这样做时，我似乎不能正确地更新回收器视图。我尝试在自定义适配器中使用通知数据设置更改（）命令，但没有给出任何结果。这是自定义适配器。

    public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {
        private Context context;
        public ArrayList Contact_id, Contact_Name, Contact_number;
        public ImageView mDelete, mMakeCall, mSendText;
        public String Latitude="0",Longitude="0";
        DatabaseHelper myDB;
        public interface OnItemClickListener {
            void onDeleteClick(int position);
        }


        CustomAdapter(Context context, ArrayList Contact_id, ArrayList Contact_Name, ArrayList Contact_number,String mLatitude,String mLongitude) {
            this.context = context;
            this.Contact_id = Contact_id;
            this.Contact_Name = Contact_Name;
            this.Contact_number = Contact_number;
            this.Latitude= mLatitude;
            this.Longitude=mLongitude;
        }

        @NonNull
        @Override
        public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

            LayoutInflater inflater = LayoutInflater.from(context);
            View view = inflater.inflate(R.layout.cardview_contact_item, parent, false);
            return new MyViewHolder(view);
        }

        @Override
        public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
            holder.Contact_id_txt.setText(String.valueOf(Contact_id.get(position)));
            holder.Contact_Name_txt.setText(String.valueOf(Contact_Name.get(position)));
            holder.Contact_Number_txt.setText(String.valueOf(Contact_number.get(position)));
        }

        @Override
        public int getItemCount() {
            return Contact_id.size();
        }

        public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
            TextView Contact_id_txt, Contact_Name_txt, Contact_Number_txt;

            public MyViewHolder(@NonNull View itemView) {
                super(itemView);
                mDelete = itemView.findViewById(R.id.Cardview_delete);
                mMakeCall = itemView.findViewById(R.id.Cardview_MakeCall);
                mSendText = itemView.findViewById(R.id.Cardview_MakeText);
                Contact_Name_txt = itemView.findViewById(R.id.CardView_Name);
                Contact_Number_txt = itemView.findViewById(R.id.CardView_Number);
                Contact_id_txt = itemView.findViewById(R.id.cardview_Contact_Id);
                SharedPreferences mPreference = PreferenceManager.getDefaultSharedPreferences(context);
                SharedPreferences.Editor editor = mPreference.edit();


                mDelete.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                     //int id= Integer.parseInt(Contact_id.getText.toString());
                     int contactId = Integer.parseInt(Contact_id_txt.getText().toString());
                     Toast.makeText(context, "int id ="+contactId+"Contact id ="+Contact_id, Toast.LENGTH_SHORT).show();
                     DatabaseHelper databaseHelper = new DatabaseHelper(context);
                     boolean success = databaseHelper.deleteOne(contactId);
                     Toast.makeText(context, "Contact Deleted", Toast.LENGTH_SHORT).show();
                     notifyDataSetChanged();
                    }

                });
                mMakeCall.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        Toast.makeText(context, "Calling Contact", Toast.LENGTH_SHORT).show();
                        Intent callIntent = new Intent(Intent.ACTION_CALL);
                        String phonenumber = Contact_Number_txt.getText().toString();
                        callIntent.setData(Uri.parse("tel:" + phonenumber));
                        try {
                            context.startActivity(callIntent);
                        } catch (Exception ex) {
                            Toast.makeText(context, "Call Failed", Toast.LENGTH_SHORT).show();
                            ex.printStackTrace();
                    }
                    }

                });
                mSendText.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        //
                        Intent smsIntent = new Intent(Intent.ACTION_SENDTO);
                        String phonenumber = Contact_Number_txt.getText().toString();
                        try {
                            SmsManager mySmsManager = SmsManager.getDefault();
                            mySmsManager.sendTextMessage(phonenumber, null, "I NEED HELP AT LATITUDE:" + Latitude + "LONGITUDE" + Longitude+" https://www.google.com/maps/search/?api=1&query="+Latitude+","+Longitude, null, null);
                            Toast.makeText(context, "Alert Message Sent", Toast.LENGTH_SHORT).show();
                            Toast.makeText(context, "LATITUDE:" + Latitude, Toast.LENGTH_SHORT).show();
                            Toast.makeText(context, "LONGITUDE:" + Longitude, Toast.LENGTH_SHORT).show();
                        }
                        catch (Exception e)
                        {
                            Toast.makeText(context, "Something went wrong/Fields are Empty", Toast.LENGTH_SHORT).show();
                        }
                        //Toast.makeText(context,"The number is "+phonenumber, Toast.LENGTH_SHORT).show();

                    }
                });


            }//End of OnCreate

            @Override
            public void onClick(View view) {

            }
        }
        //public void removeItem(int position){}

    }

它工作正常，但只有在我退出并输入main活动一次后才会更新。我尝试在mainactivity本身中实现notifyDataSetChanged（）方法，但是当我这样做时，我得到了一个nullpointerexception。

        ImageView mDelete;
    mDelete = findViewById(R.id.Cardview_delete);
    mDelete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //int id= Integer.parseInt(Contact_id.getText.toString());
            customAdapter.notifyDataSetChanged();
        }
    });

这是错误代码

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rakshakmk1/com.example.rakshakmk1.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.rakshakmk1.MainActivity.onCreate(MainActivity.java:150)
    at android.app.Activity.performCreate(Activity.java:7802)
    at android.app.Activity.performCreate(Activity.java:7791)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

XML布局：RecyclerView/Cardview

 <?xml version="1.0" encoding="utf-8"?>
 <androidx.cardview.widget.CardView 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:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp">

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="102dp"
    >

    <ImageView
        android:id="@+id/Cardview_bg"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:srcCompat="@drawable/dialog_rounded_bg"
        tools:layout_editor_absoluteX="0dp"
        tools:layout_editor_absoluteY="0dp" />

    <ImageView
        android:id="@+id/Cardview_MakeText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0"
        app:srcCompat="@drawable/ic_location_icon_final" />

    <ImageView
        android:id="@+id/Cardview_delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.981"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.05"
        app:srcCompat="@drawable/ic_delete_circle_icon_final" />

    <TextView
        android:id="@+id/CardView_Name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Emergency Contact"
        android:textColor="#000000"
        android:textSize="30sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.101"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.259"
        android:paddingRight="50sp"/>

    <TextView
        android:id="@+id/CardView_Number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Number"
        android:textColor="#858585"
        android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.079"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.794" />

    <ImageView
        android:id="@+id/Cardview_MakeCall"
        android:layout_width="37dp"
        android:layout_height="36dp"
        app:layout_constraintBottom_toBottomOf="@+id/Cardview_MakeText"
        app:layout_constraintEnd_toStartOf="@+id/Cardview_MakeText"
        app:layout_constraintHorizontal_bias="0.974"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/Cardview_MakeText"
        app:layout_constraintVertical_bias="0.444"
        app:srcCompat="@drawable/ic_call_icon_final" />

    <TextView
        android:id="@+id/cardview_Contact_Id"
        android:layout_width="23dp"
        android:layout_height="15dp"
        android:text="TextView"
        app:layout_constraintBottom_toTopOf="@+id/CardView_Name"
        app:layout_constraintEnd_toStartOf="@+id/Cardview_delete"
        app:layout_constraintHorizontal_bias="0.469"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

 </androidx.cardview.widget.CardView>

XML布局：主要活动

<?xml version="1.0" encoding="utf-8"?>
   <androidx.constraintlayout.widget.ConstraintLayout        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:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/gradient_background"
tools:context=".MainActivity">
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/activity_rounded_bg"
    android:layout_marginTop="50dp">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/RecyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clipToPadding="true"
        android:paddingHorizontal="0dp"
        android:paddingTop="10dp"
        tools:layout_editor_absoluteX="0dp"
        tools:layout_editor_absoluteY="67dp"
        tools:listitem="@layout/cardview_contact_item">

    </androidx.recyclerview.widget.RecyclerView>

</RelativeLayout>
<ImageButton
    android:id="@+id/btnAddContact"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="#00FFFFFF"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.498"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="1.0"
    app:srcCompat="@drawable/ic_add_icon" />
   </androidx.constraintlayout.widget.ConstraintLayout>

这是创建arraylist的main活动。

        public class MainActivity extends AppCompatActivity {
        private static final String TAG = "MainActivity";
        //widgets
        public ImageButton eAddContact;
        RecyclerView recyclerView;
    
        DatabaseHelper myDB;
        ArrayList<String> Contact_id, Contact_Name, Contact_Number;
        CustomAdapter customAdapter;
        Button btnEnterContact;
    
        private FusedLocationProviderClient fusedLocationProviderClient;
        //Google's api for location services.
    
        //private final int REQUEST_CHECK_CODE=8989;
        private LocationSettingsRequest.Builder builder;
        private String mLatitude,mLongitude;
        private static final int REQUEST_SMS = 0;
        private static final int REQUEST_LOCATION = 1;
        private static final int REQUEST_CALL =2;
        Intent mIntent;
        LocationManager locationManager;
    
        LocationRequest locationRequest;
        LocationCallback locationCallback;
    
    
    
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
    
            //permissions
    
            if(ContextCompat.checkSelfPermission(this,Manifest.permission.SEND_SMS)!=PackageManager.PERMISSION_GRANTED)
            {
                //if permission is not granted then check if user has denied
                if(ActivityCompat.shouldShowRequestPermissionRationale(this,Manifest.permission.SEND_SMS)){
    
                }else
                {
                    //popup for asking permission
                    ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.SEND_SMS},REQUEST_SMS);
                }
            }
            if(ContextCompat.checkSelfPermission(this,Manifest.permission.ACCESS_FINE_LOCATION)!=PackageManager.PERMISSION_GRANTED)
            {
                //if permission is not granted then check if user has denied
                if(ActivityCompat.shouldShowRequestPermissionRationale(this,Manifest.permission.ACCESS_FINE_LOCATION)){
    
                }else
                {
                    //popup for asking permission
                    ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.ACCESS_FINE_LOCATION},REQUEST_LOCATION);
                }
            }
            if(ContextCompat.checkSelfPermission(this,Manifest.permission.CALL_PHONE)!=PackageManager.PERMISSION_GRANTED)
            {
                //if permission is not granted then check if user has denied
                if(ActivityCompat.shouldShowRequestPermissionRationale(this,Manifest.permission.CALL_PHONE)){
    
                }else
                {
                    //popup for asking permission
                    ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.CALL_PHONE},REQUEST_CALL);
                }
            }
    
            eAddContact = findViewById(R.id.btnAddContact);
            eAddContact.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Log.d(TAG, "onClick:opening dialog");
                    Dialog_AddContact dialog = new Dialog_AddContact();
                    dialog.show(getSupportFragmentManager(), "Add Contact Dialog");
                }
            });
            //Toast.makeText(getApplicationContext(),"@#",Toast.LENGTH_SHORT).show();
            myDB = new DatabaseHelper(MainActivity.this);
            Contact_id = new ArrayList<>();
            Contact_Name = new ArrayList<>();
            Contact_Number = new ArrayList<>();
            recyclerView = findViewById(R.id.RecyclerView);
            Cursor cursor= myDB.getEveryone();
            customAdapter = new CustomAdapter(MainActivity.this, Contact_id, Contact_Name, Contact_Number,mLatitude,mLongitude);
    
            //set all the properties of LocationRequest
            locationRequest = new LocationRequest();
            //how often does location check occur
            locationRequest.setInterval(1000*30);
            locationRequest.setFastestInterval(1000*50);
            locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
            locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
            //Display cardview data
            recyclerView.setAdapter(customAdapter);
            recyclerView.setLayoutManager(new LinearLayoutManager(MainActivity.this));
            customAdapter.notifyDataSetChanged();
            //update gps data
            updateGPS();
            storeDataInArrays();
            /*
            ImageView mDelete;
            mDelete = findViewById(R.id.Cardview_delete);
            mDelete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    //int id= Integer.parseInt(Contact_id.getText.toString());
                    customAdapter.notifyDataSetChanged();
                }
            });
             */
        }
    
        @Override
        public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
            super.onRequestPermissionsResult(requestCode, permissions, grantResults);
            //will check requestCode
            switch(requestCode)
            {
                case REQUEST_SMS:
                {
                    //check if length of grantResults is greater than 0 and equal to PERMISSION_GRANTED
                    if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED)
                    {
                        Toast.makeText(this,"SMS Permission Granted",Toast.LENGTH_LONG).show();
                    }
                    else
                    {
                        Toast.makeText(this,"SMS Permission Denied",Toast.LENGTH_LONG).show();
                    }
                }
                case REQUEST_LOCATION:
                {
                    //check if length of grantResults is greater than 0 and equal to PERMISSION_GRANTED
                    if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED)
                    {
                        Toast.makeText(this,"Location Permission Granted",Toast.LENGTH_LONG).show();
                        updateGPS();
                    }
                    else
                    {
                        Toast.makeText(this,"Location Permission Denied",Toast.LENGTH_LONG).show();
                    }
                }
                case REQUEST_CALL:
                {
                    //check if length of grantResults is greater than 0 and equal to PERMISSION_GRANTED
                    if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED)
                    {
                        Toast.makeText(this,"Call Permission Granted",Toast.LENGTH_LONG).show();
                        updateGPS();
                    }
                    else
                    {
                        Toast.makeText(this,"Call Permission Denied",Toast.LENGTH_LONG).show();
                    }
                }
            }//switch
        }
    
        private void updateGPS(){
            //get permissions from the user to track GPS
            //get current location
            //update string
            fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(MainActivity.this);
            if(ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)== PackageManager.PERMISSION_GRANTED){
                //user gave the permissions
                fusedLocationProviderClient.getLastLocation().addOnSuccessListener(this, new OnSuccessListener<Location>() {
                    @Override
                    public void onSuccess(Location location) {
                        //we got permissions. put the values of location.
                        updateLocation(location);
                    }
                });
            }
            else{
                if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.M){
                    requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION},REQUEST_LOCATION);
                }
            }
    
        }
    
        private void updateLocation(Location location) {
            //update the location of the person
             mLatitude = String.valueOf(location.getLatitude());
             mLongitude = String.valueOf(location.getLongitude());
            Toast.makeText(this,"Latitude = "+mLatitude,Toast.LENGTH_SHORT).show();
            Toast.makeText(this,"Longitude = "+mLongitude,Toast.LENGTH_SHORT).show();
            Cursor cursor= myDB.getEveryone();
            recyclerView.setAdapter(new CustomAdapter(MainActivity.this, Contact_id, Contact_Name, Contact_Number,mLatitude,mLongitude));
            recyclerView.invalidate();
        }
    
    
    
        void storeDataInArrays() {
            customAdapter.notifyDataSetChanged();
            Contact_id.clear();
            Contact_Name.clear();
            Contact_Number.clear();
            Cursor cursor = myDB.getEveryone();
            if (cursor.getCount() == 0) {
                //Add blank page
            } else {
                while (cursor.moveToNext()) {
                    Contact_id.add(cursor.getString(0));
                    Contact_Name.add(cursor.getString(1));
                    Contact_Number.add(cursor.getString(2));
                }
            }
            recyclerView.setAdapter(new CustomAdapter(MainActivity.this, Contact_id, Contact_Name, Contact_Number,mLatitude,mLongitude));
            customAdapter.notifyDataSetChanged();
        }
        public void removeItem(int position){
            Contact_id.remove(true);
            storeDataInArrays();
            customAdapter.notifyDataSetChanged();
        }
    
        //public void onRequestPermissionResult(int requestCOde,String permissions[],int[] grantResults){}//method
        public void onLocationChanged(Location location) {
    
        }
    
    
        public void onProviderDisabled(String provider) {
            Log.d("Latitude","disable");
        }
    
    
        public void onProviderEnabled(String provider) {
            Log.d("Latitude","enable");
        }
    
        public void onStatusChanged(String provider, int status, Bundle extras) {
            Log.d("Latitude","status");
        }
    }

我好像做错了什么？非常感谢您的帮助。




Answer 1

我不是很确定，但是更新ArrayList应该可以做到这一点。

 mDelete.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                     //int id= Integer.parseInt(Contact_id.getText.toString());
                     int contactId = Integer.parseInt(Contact_id_txt.getText().toString());
                     Toast.makeText(context, "int id ="+contactId+"Contact id ="+Contact_id, Toast.LENGTH_SHORT).show();
                     DatabaseHelper databaseHelper = new DatabaseHelper(context);
                     boolean success = databaseHelper.deleteOne(contactId);
                     Contact_id.remove(Integer.valueOf(contactId));
                     Toast.makeText(context, "Contact Deleted", Toast.LENGTH_SHORT).show();
                     notifyDataSetChanged();
                }

联系人姓名和联系人号码可能也需要更新，但这取决于MainActivity代码如何处理。