I'm particularly new to this field. I'm trying to create a login page using fragments and it crashed when I tried to run it. I checked the logcat, turns out its a NullPointerException. It highlighted the error here:

register = (Button) findViewById(R.id.RegisterUser);
register.setOnClickListener(this);

Here is my code

this is mainactivity

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView register;

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

        register = (Button) findViewById(R.id.RegisterUser);
        register.setOnClickListener(this);

        ViewPager viewPager = findViewById(R.id.viewPager);

        AuthenticationPagerAdapter pagerAdapter = new 
        AuthenticationPagerAdapter(getSupportFragmentManager());
        pagerAdapter.addFragmet(new LoginFragment());
        pagerAdapter.addFragmet(new RegisterFragment());
        viewPager.setAdapter(pagerAdapter);
    }

    public void onClick(View v){
        switch (v.getId()){
            case R.id.RegisterUser:
            startActivity(new Intent(this, RegisterUser.class));
            break;
        }
    }

    class AuthenticationPagerAdapter extends FragmentPagerAdapter {
        private ArrayList<Fragment> fragmentList = new ArrayList<>();

        public AuthenticationPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int i) {
            return fragmentList.get(i);
        }

        @Override
        public int getCount() {
            return fragmentList.size();
        }

        void addFragmet(Fragment fragment) {
            fragmentList.add(fragment);
        }
    }
}

CodePudding user response：

It seems you define the global field private TextView register; but you want to cast it to Button register = (Button) findViewById(R.id.RegisterUser);

Please check your XML file and make sure what's your element TextView or Button.

CodePudding user response：

can you please check your activity_main.xml file check into that is a Button or Textview