Why Am I Getting a NullPointerException When Accessing Views in My LoginActivity?

NullPointerException: Attempting to Retrieve Callback fromUninitialized Window

When navigating from SplashActivity to LoginActivity, the app encounters an error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

This error indicates that LoginActivity is trying to access a view component before it has been properly initialized.

Cause

The specific cause of the error lies in the LoginActivity.java code, where the class members are initialized before setContentView() is called in onCreate(). This leads to a situation where the views do not exist yet when the class members try to find them.

Solution

To fix the issue, declare the view members in the class without initialization:

private EditText usernameField, passwordField;
private TextView error;
private ProgressBar progress;

Then, initialize the members within onCreate() after setContentView() has been called:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);

    usernameField = (EditText)findViewById(R.id.username);
    passwordField = (EditText)findViewById(R.id.password);
    error = (TextView)findViewById(R.id.error);
    progress = (ProgressBar)findViewById(R.id.progress);
}

Additional Advice

While not directly related to the error, it is recommended to replace Timer with Handler when running a task on the UI thread:

new Handler().postDelayed(new Runnable() {
  @Override
  public void run() {
    Intent intent = new Intent(SplashActivity.this, LoginActivity.class);
    startActivity(intent);
    finish();
  }
}, 1500);

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