Android how to call Activity data type from another class in Main Activity?

Question

I have this code separate class which makes a Snackbar to be displayed within my application, But with my current implementation I am getting a 'java.lang.NullPointerException'. How do I implement it in my main class properly?

here is my snack bar class:

public class SnackBarUtils
{
private static SnackBarUtils mInstance = null;
private  Snackbar mSnackBar;

private SnackBarUtils()
{

}

public static SnackBarUtils getInstance()
{
    if (mInstance == null)
    {
        mInstance = new SnackBarUtils();
    }
    return mInstance;
}

public void hideSnackBar()
{
    if (mSnackBar != null)
    {
        mSnackBar.dismiss();
    }
}

public void showProblemSnackBar(final Activity activity, final String message)
{
    mSnackBar = Snackbar.make(activity.findViewById(android.R.id.content), message, 
    Snackbar.LENGTH_INDEFINITE);
    // Changing action button text color
    View sbView = mSnackBar.getView();
    TextView textView = sbView.findViewById(com.google.android.material.R.id.snackbar_text);
    mSnackBar.setAction("x", new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            //Call your action method here
            mSnackBar.dismiss();
        }
    });
    textView.setTextColor(Color.WHITE);
    sbView.setBackgroundColor(Color.RED);
    textView.setMaxLines(3);
    mSnackBar.show();
}
}

This is my current implementation within main activity, I have already Initialized the snackbar class like this:

SnackBarUtils snackBarUtils;

and then called it like this:

snackBarUtils.showProblemSnackBar(MainActivity.this, mPlainTextResponse);

what am I doing wrong? Or what is the correct way to do this?

Answer 1

First of all, you would share the stacktrace of the NPE for more context.

For the snackbar utility:
If you are using callbacks, then you can use the utility for displaying a snackbar with that callback as parameter:

interface onProblemSnackbarClickedListener {
  void onActionClicked(View view);
}
...
/* inside SnackBarUtils.java */
...
public static void showProblemSnackbar(View view, @StringRes int message, onProblemSnackbarClickedListener listener){
   Snackbar mSnackBar = Snackbar.make(view,message,Snackbar.LENGTH_INDEFINITE)
    .setAction("x", new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        listener.onActionClicked(v);
        mSnackBar.dismiss();
      }
  })
  mSnackbar.show();
}

The callback could work for the need to listen to it in the activity/fragment.

For the styling of the Snackbar, you can see this related question: Style SnackBar in theme app.

Keep in mind the migration from "Support design" to MDC (Material design components), that facilitates the global styling of the snackbar with theme attributes.