Xamarin android System.NullReferenceException: Object reference not set to an instance of an object

Question

I am new to mobile development. I am working on android using xamarin in visual studio 2015. I am following this sample code. I am deploying my app on my device and it's running good. I have basically following functions

1. Insert
2. Display
3. Update
4. Delete

All of the functions are running good but on update when i click the update button in update layout first it gets all the data from DB(SQLITE) and then it displays it in Edit Text Boxes In sample code you can see the updateEmployee.cs code. So while updating i m getting the bellow error

I am getting null value in dName while there is a name in name field

Above i have declared the dName dEmail etc like bellow

TextView dName, dEmail, dPhone, dDesignation;
    String name, email, phone, designation;

Also in initialize method i am also getting null values and eName etc in initialize is the id in complete_data layout whose axml is as follows

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<ScrollView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <ListView
            android:id="@+id/listView1"
            android:layout_width="match_parent"
            android:layout_height="350dp"
            android:divider="#000"
            android:dividerHeight="1dp" />
        <TextView
            android:id="@+id/eName"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Name" />
        <TextView
            android:id="@+id/eEmail"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Email" />
        <TextView
            android:id="@+id/ePhone"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Phone" />
        <TextView
            android:id="@+id/eDesignation"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Designation" />
    </LinearLayout></ScrollView></LinearLayout>

Update 1:

Bellow is the code in which i am getting this exception

 void List_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
    {
        click_Employee = e.Position + 1;
        ICursor c = dbHelper.getSingleEntry(click_Employee);
        c.MoveToFirst();
        name = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_NAME));
        email = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_EMAIL));
        phone = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_PHONE));
        designation = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_DESIGNATION));
        dName.Text = name;
        dEmail.Text = email;
        dPhone.Text = phone;
        dDesignation.Text = designation;
    }

The name field is in string and i am assigning this string to my edit text dName and etc as shown in code above. At dName.text = name i am getting this null exception, while the name field contain the name. Is there any other way to do it?

I am not sure what am i missing. Any help would be highly appreciated

Answer 1

The most probable cause for this problem is that FindViewById is either not called or it doesn't actually assign dname.

This can have multiple causes:

1. Your initialize method is never called
2. It is called after List_ItemClick
3. It is called but assigning the view fails because in XML use have TextView and in code the type is EditText

Set two breakpoints. One in List_ItemClick and one in initialize. Check which one is called first. Step through initialize to make sure views are found and assigned.

Answer 2

First of all, I can see from your code that you declare dName as a TextView but when you use FindViewById your are parsing EditText instead, so make sure that you use TextView in both places.

Second, make sure that your code runs in the following sequence: 1- Declare dName as a TextView. 1- Assign a value to "name" variable. 2- Use FindViewById to find eName. 3- Assign dName a value.

so, your code should look like the following order:

TextView dName;
string name = "Some name"; // or you can get the name from database
dName = (TextView)FindViewById(Resource.Id.eName);
dName.Text = name;

Answer 3

This is a usual Problem While building again am again , here are the steps I get resolve:

1. If you xamarin Auto Update is on then your check your project setting and target Android version ,, If it is updated then (a) downgrade it or (b) Download the new versions SDK by going to Tools--> SDK manager
2. Clean up your simulator with all instances of APP
3. Clean Build
4. Shudown Computer..then Start system ( dont restart it )