How to validate registration data and insert it into SQLite Database?

I can insert registration data successfully. But I want to validate register form. So, I do validation code. The validation code is ok, no errors. But I can't relate between insert data code and validation code.

   public void addData() {
        save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final String validationUserName = username.getText().toString();
                final String validationEmail = email.getText().toString();
                final String validationPass = password.getText().toString();

                if (!isValidUserName(validationUserName)) {
                    username.setError("User Name isn't empty");
                }
                if (!isValidEmail(validationEmail)) {
                    email.setError("invalid Email");
                }
                if (!isValidPassword(validationPass)) {
                    password.setError("Password must be at least 6 characters");
                }
                boolean isInserted = myDB.insertData(username.getText().toString(), email.getText().toString(), password.getText().toString());
                if (isInserted = true) {
                    Toast.makeText(People.this, "Save Successfully !", Toast.LENGTH_SHORT).show();
                } else if (isInserted = false) {
                    Toast.makeText(People.this, "Please Input Data !", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    private boolean isValidUserName(String username) {
        if (username != null) {
            return true;
        }
        return false;
    }

    private boolean isValidEmail(String email) {
        String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@"
                + "[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";

        Pattern pattern = Pattern.compile(EMAIL_PATTERN);
        Matcher matcher = pattern.matcher(email);
        return matcher.matches();
    }

    private boolean isValidPassword(String pass) {
        if (pass != null && pass.length() > 6) {
            return true;
        }
        return false;
    }