App crashes when I press "continue" button (transitioning between activities)

Question

I am creating an app where you log in and then access a database of files unique to each user account. I have a continue button linking the "LoginActivity" and "MainActivity" activities together. The code that I have in the LoginActivity file is this:

@Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.email_create_account_button:
                createAccount(mEdtEmail.getText().toString(), mEdtPassword.getText().toString());
                break;
            case R.id.email_sign_in_button:
                signIn(mEdtEmail.getText().toString(), mEdtPassword.getText().toString());
                break;
            case R.id.sign_out_button:
                signOut();
                break;
            case R.id.continue_button:
                Button btn = (Button)findViewById(R.id.continue_button);
                startActivity(new Intent(LoginActivity.this, MainActivity.class));
                break;
        }
    }

and on the MainActivity side I have this:

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

        upload_button = findViewById(R.id.upload_button);
        showall_button = findViewById(R.id.showall_button);
        progressBar = findViewById(R.id.progressBar);
        imageView = findViewById(R.id.imageView);

        progressBar.setVisibility(View.INVISIBLE);

        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent galleryIntent = new Intent();
                galleryIntent.setAction(Intent.ACTION_GET_CONTENT);
                galleryIntent.setType("image/*");
                startActivityForResult(galleryIntent , 2);
            }
        });

What is wrong with my code? I can't seem to figure it out. Please let me know if you need more code from my project. Thanks!

Answer 1

You should initialize your buttons and after that, set onclicklistener to them. For the complete explanation visit Android App Crashes on Button Click

Answer 2

According to your logcat, it seems that, you are referencing an resource ID which doesn't exists on your XML ( activity_main.xml ) file.
Check whether the ID imageView exists or not. It might not present in your layout file or it may have different name. Make the ID name same both in activity_main.xml side and MainActivity side.