Unable to instantiate activity: Chronometer (Android Studio)

Question

I'm running into an error after trying to mess around and add a simple stopwatch. Could someone point me in the right direction? I have very little experience with Java and I'm just learning right now.

I wanted to create an increment counter that also started counting time as soon as your increment up by 1.

The Error I'm getting:

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.countingapp/com.example.android.countingapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object referenc"

My Code:

package com.example.android.countingapp;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Chronometer;

public class MainActivity extends AppCompatActivity {
    TextView showValue;
    TextView showTimeValue;
    int counter = 0;
    Chronometer simpleChronometer = (Chronometer) findViewById(R.id.TimeValue); // initiate a chronometer

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    showValue = (TextView) findViewById(R.id.CountValue);
    showTimeValue = (TextView) findViewById(R.id.TimeValue);
}

public void CountIncrease (View view){
    // On each click this button will increase
    counter ++;
    showValue.setText(Integer.toString(counter));
    simpleChronometer.start(); // start a chronometer
}
public void CountDecrease (View view){
    // On each click this button will increase
    counter --;
    showValue.setText(Integer.toString(counter));
}

public void CountReset (View view){
    // On each click this button will increase
    counter = 0;
    showValue.setText(Integer.toString(counter));
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

XML:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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/content_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.example.android.countingapp.MainActivity"
    tools:showIn="@layout/activity_main">

    <Button
        android:text="DecreaseButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="CountDecrease"
        android:id="@+id/button2"
        android:layout_alignBaseline="@+id/button"
        android:layout_alignBottom="@+id/button"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_toRightOf="@+id/button3"
        android:layout_toEndOf="@+id/button3" />

    <Button
        android:text="ResetButton"
        android:onClick="CountReset"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="64dp"
        android:id="@+id/button3" />

    <Button
        android:text="IncreaseButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="CountIncrease"
        android:id="@+id/button"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_toLeftOf="@+id/button3"
        android:layout_toStartOf="@+id/button3" />

    <TextView
        android:text="CountDisplay"
        android:id ="@+id/CountValue"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="25dp"
        android:layout_above="@+id/button2"
        android:layout_centerHorizontal="true" />

    <Chronometer
        android:text="TimeDisplay"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/CountValue"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="46dp"
        android:id="@+id/TimeValue" />

</RelativeLayout>

Answer 1

This line

Chronometer simpleChronometer = (Chronometer) findViewById(R.id.TimeValue);

should go inside your onCreate method, below

setContentView(R.layout.activity_main);

That is because the setContentView method tells the activity which layout to use, hence it allows it to find views using their ids with the findViewById method.

Here's how it should look

public class MainActivity extends AppCompatActivity { 
TextView showValue;
TextView showTimeValue;
int counter = 0;
//Declare here the simpleChonometer object
Chronometer simpleChronometer;

@Override 
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Initiate here the simpleChronometer object
simpleChronometer =  (Chronometer) findViewById(R.id.TimeValue); // initiate a chronometer

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

FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
    @Override 
    public void onClick(View view) {
        Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                .setAction("Action", null).show(); 
    } 
}); 

showValue = (TextView) findViewById(R.id.CountValue);
showTimeValue = (TextView) findViewById(R.id.TimeValue);
}
...

Answer 2

After initializing Chronometer as simpleChronometer, put your

simpleChronometer = (Chronometer) findViewById(R.id.TimeValue); // initiate a chronometer

under onCreate() like the way you have done for floatingActionButton.