Sending data from a second activity to the first one doesn't work Android

Question

I am currently working on an app that allows you to make a list of notes:

The list is viewable in the first activity
The new note button leads to a second activity with edit text and a few text formatting buttons ( Bold, Italic, bigger text, smaller)
The app allows you on long clicks to either edit or delete the notes in the list.

The problem is when I send data from one activity to another I get this error on the logs:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

And that happens only when I try to send the data back to the first activity. When I try to save it internally from a button in the second activity the same method:

getText().toString()

works just fine. Here is the code for sending/receiving data between activities and and the saving method.

public void sendMessage(View view)
{
    editText = (EditText) findViewById(R.id.add_text);
    String message = editText.getText().toString();
    Intent intent  = new Intent(this, MainActivity.class);
    intent.putExtra(key_Message, message);
    startActivity(intent);
}


@Override
protected void onResume() {
    super.onResume();
    Intent intent = getIntent();
    String message = intent.getStringExtra(key_Message);
    list.add(message);
    adapter.notifyDataSetChanged();
}

And here is the method for saving text internally ( which works fine). Note that I added the sendMessage function in the writeMessage(but commented it)

 public void writeMessage(View view)
{
    String Message = editText.getText().toString();
    String file_name = "Notes_file";
    try {
        FileOutputStream fileOutputStream = openFileOutput(file_name, MODE_PRIVATE);
        fileOutputStream.write(Message.getBytes());
        fileOutputStream.close();
        Toast.makeText(getApplicationContext(),"Message has been saved", Toast.LENGTH_SHORT).show();
        //String message = editText.getText().toString();
        //Intent intent  = new Intent(this, MainActivity.class);
        //intent.putExtra(key_Message, message);
        //startActivity(intent);

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

Also another small problem I couldn't wrap my head around either:

public void shrinkText(View view)
{   float modifySize = editText.getTextSize();
    modifySize = modifySize - 3;
    editText.setTextSize(modifySize);
}

Is a small method that is supposed to shrinkText from an edit text when the user clicks a button. It always increases text. Some help would be appreciated.

public void writeMessage(View view)
{
    String Message = editText.getText().toString();
    String file_name = "Notes_file";
    try {
        FileOutputStream fileOutputStream = openFileOutput(file_name, MODE_PRIVATE);
        fileOutputStream.write(Message.getBytes());
        fileOutputStream.close();
        Toast.makeText(getApplicationContext(), "Message has been saved", Toast.LENGTH_SHORT).show();
        String message = editText.getText().toString();
        Intent intent  = new Intent();
        intent.putExtra(key_edit, message);
        setResult(RESULT_OK, intent);
        finish();


    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

 @Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == 1){
        if(resultCode == RESULT_OK){
            String item_tobeadded1;
            item_tobeadded1 = data.getStringExtra(key_edit);
            list.add(item_tobeadded1);
            //adapter.notifyDataSetChanged();
            adapter = new ArrayAdapter<String>(this,android.R.layout.simple_expandable_list_item_1, list);
            list_view.setAdapter(adapter);
        }
    }
}

http://stackoverflow.com/a/14292451/2435402 This is a great answer to help you implement your logic. — em_, Jan 06 '16 at 16:10
The sending works now but when I add the specific item to the listview it does not appear. — user3402719, Jan 06 '16 at 16:31
Call the adapter of your list view and invoke notifyDataSetChanged when you send the object — Laurent Meyer, Jan 06 '16 at 16:57
Possible duplicate of [How to pass data from 2nd activity to 1st activity when pressed back? - android](http://stackoverflow.com/questions/14292398/how-to-pass-data-from-2nd-activity-to-1st-activity-when-pressed-back-android) — Dhaval Parmar, Jan 06 '16 at 18:16

Pankaj Nimgade · Accepted Answer · 2016-01-07T20:12:06.387

As already suggested what you can do is start your second activity for with the data on the listview item you just clicked when you are editing, or when you crate a new don't pass anything.

In this manner you would be able to edit as well as create the new Note without making much changes in the code.

int RESPONSE_CODE = 123; // from this code will will differentiate if 
                         // the activity which we started actually did the task or not

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

            Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
            intent.putString("para1","arg1");
            intent.putString("para2","arg2");
            intent.putString("para3","arg3");
            intent.putString("para4","arg4");
            startActivityForResult(intent, RESPONSE_CODE);
        }
    });

in NoteEditActivity.class you can receive your parameters if there were something. As while creating new Note para1,para2, para3 & para4 would be empty. But if the Note already exist you would have to edit that

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Intent myIntent = getIntent();
    String arg1 = myIntent.getStringExtra("para1");
    String arg2 = myIntent.getStringExtra("para2");
    String arg3 = myIntent.getStringExtra("para3");
    String arg4 = myIntent.getStringExtra("para4");
    // here you have to check that they or not null to differentiate 
    // if it is a new Note to be created OR you have to edit.
    // you should probably use some another way to figure this out, i am writing this because i would not be using it :)

}

And once you are done creating or editing your Note, attach the relevant data to the intent and finish the activity like this

Intent intent = new Intent();
intent.putExtra("para1","edited_data_1");
intent.putExtra("para2","edited_data_2");
intent.putExtra("para3","edited_data_3");
intent.putExtra("para4","edited_data_4");
setResult(RESULT_OK, intent);        
finish();

if the Task was successful you will set the result to RESULT_OK attach the intent and you are done

in the previous activity you have to override a method called onActivityResult() this method receives the data from the activity you had started to do some task,

public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 1) {
         if(resultCode == RESULT_OK){

            String arg1 = data.getStringExtra("para1");
            String arg2 = data.getStringExtra("para2");
            String arg3 = data.getStringExtra("para3");
            String arg4 = data.getStringExtra("para4");
            // if you receive the data here,
            // you can add another element to List from which the -
            //`ListView` is populated and call `notifyDataSetChanged()` on the adapter.
            // like this `adapter.notifyDataSetChanged();` it will update the `listview` -
            //with new data that you received from the `NoteEditActivity.class` 

             adapter.notifyDataSetChanged(); // I am assuming you would add the changed item to the List
         }     
    }
}

Update, I have created a dummy code for you and it does works, i have tested it, I have also uploaded it on Github that you may check it there

NoteListActivity.java

public class NoteListActivity extends Activity {

    private ListView listView;
    private ArrayList<String> strings;
    public static final String NEW_ELEMENT = "NEW_ELEMENT";
    public static final String ELEMENT_VALUE = "ELEMENT_VALUE";
    public static final String ELEMENT_POSITION = "ELEMENT_POSITION";
    private ArrayAdapter<String> adapter;

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

        listView = (ListView) findViewById(R.id.NoteListActivity_listView);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                String text = (String) listView.getItemAtPosition(position);
                Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
                intent.putExtra(NEW_ELEMENT, false);
                intent.putExtra(ELEMENT_POSITION, position);
                intent.putExtra(ELEMENT_VALUE, text);
                startActivityForResult(intent, 123);
            }
        });

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.NoteListActivity_fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
                intent.putExtra(NEW_ELEMENT, true);
                startActivityForResult(intent, 123);
            }
        });

        setUpList();

        adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.simple_list_item_1, strings);
        listView.setAdapter(adapter);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.d("NoteListActivity1",""+data.getStringExtra(NoteListActivity.ELEMENT_VALUE));

        if (requestCode == 123) {
            if (resultCode == RESULT_OK) {
                Log.d("NoteListActivity2",""+data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
                boolean isNewElement = data.getBooleanExtra(NoteListActivity.NEW_ELEMENT, false);
                if (isNewElement) {
                    strings.add("" + data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
                    adapter.notifyDataSetChanged();
                } else {
                    strings.set(data.getIntExtra(NoteListActivity.ELEMENT_POSITION, 0), "" + data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
                    adapter.notifyDataSetChanged();
                }
            }
        }
    }

    private void setUpList() {
        strings = new ArrayList<>();
        for (int i = 0; i < 4; i++) {
            strings.add("Element_1_" + i);
        }
    }
}

activity_note_list.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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:fitsSystemWindows="true"
    tools:context="com.nimgade.pk.mytutorialapplication.MainActivity">

    <LinearLayout 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:orientation="vertical"
        tools:context="activities.list.first.NoteListActivity">


        <ListView
            android:id="@+id/NoteListActivity_listView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </LinearLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/NoteListActivity_fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_menu_add" />

</android.support.design.widget.CoordinatorLayout>

NoteEditActivity.java

public class NoteEditActivity extends Activity {

    private EditText editText;
    private Button button;
    private boolean isNewElement;
    private int position;

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

        editText = (EditText) findViewById(R.id.NoteEditActivity_editText);
        button = (Button) findViewById(R.id.NoteEditActivity_button);

        Intent myIntent = getIntent();
        isNewElement = myIntent.getBooleanExtra(NoteListActivity.NEW_ELEMENT, false);

        if (!isNewElement) {
            editText.setText("" + myIntent.getStringExtra(NoteListActivity.ELEMENT_VALUE));
            position = myIntent.getIntExtra(NoteListActivity.ELEMENT_POSITION,0);
        }

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String text = editText.getText().toString();
                if (text != null && text.trim().length() > 0) {
                    Intent intent = new Intent();
                    Log.d("NoteEditActivity",""+text);
                    intent.putExtra(NoteListActivity.ELEMENT_VALUE, text);
                    intent.putExtra(NoteListActivity.NEW_ELEMENT, isNewElement);
                    if (!isNewElement) {
                        intent.putExtra(NoteListActivity.ELEMENT_POSITION, position);
                    }
                    setResult(RESULT_OK, intent);
                    finish();
                } else {
                    Toast.makeText(getApplicationContext(), "Kindly write a valid element name", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

activity_note_edit.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context="activities.list.first.NoteEditActivity">


    <EditText
        android:id="@+id/NoteEditActivity_editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/NoteEditActivity_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Save"
        android:textAllCaps="false" />
</LinearLayout>

Its working.. but still it won't add the items to the list and I use the list.add(item) and adapter.notifyDataSetChanged(); — user3402719, Jan 07 '16 at 08:32
@user3402719 ok, in that case re initiate the adapter after adding the item to the list and and set this adapter to the listview — Pankaj Nimgade, Jan 07 '16 at 08:44
Still nothing... I add the item then reinitiate the adapter and re-set it for use for the list — user3402719, Jan 07 '16 at 08:51
Last codeblock. It sends the data and won't add it to the list. — user3402719, Jan 07 '16 at 08:57
yes... only string items in the list as it only contains notes — user3402719, Jan 07 '16 at 09:07
in which activities did you write **onActivityResult** and **writeMessage()** method? — Pankaj Nimgade, Jan 07 '16 at 09:24
onActivityResult is on the main activity which receives data from all the other activities and the write message is a common method in the editNote Activity and the add note activity — user3402719, Jan 07 '16 at 10:05
do you save it in some file while you re direct to the previous activity — Pankaj Nimgade, Jan 07 '16 at 10:12
No.. you have the option to save it internally but on another button. — user3402719, Jan 07 '16 at 10:50
@user3402719, i have made some code for you and also uploaded the code on github, it is tested and working https://github.com/pankajnimgade/Tutorial/blob/master/app/src/main/java/activities/list/first/NoteListActivity.java — Pankaj Nimgade, Jan 07 '16 at 20:18

Sending data from a second activity to the first one doesn't work Android

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