What is the correct way to pass data from one Activity to another Activity?

Question

Java

I have a simple application that interacts with firebase
In the firebase base, there are only two values ​​\u200b\u200bthis name and url



My Item class

public class ItemFirebase {

    String name, url;

    public String getName() {
        return name;
    }

    public String getUrl() {
        return url;
    }
}

My Adapte

public class MyAdapter extends RecyclerView.Adapter <MyAdapter.MyViewHolder> {

    MainActivity context;

    ArrayList<ItemFirebase> list;

    public MyAdapter(MainActivity context, ArrayList<ItemFirebase> list) {
        this.context = context;
        this.list = list;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(context).inflate(R.layout.item,parent,false);
        return  new MyViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

        ItemFirebase itemFirebase = list.get(position);
        holder.name.setText(itemFirebase.getName());
        holder.data.setText(itemFirebase.getUrl());


    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        TextView name, data;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);

            name = itemView.findViewById(R.id.name);
            data = itemView.findViewById(R.id.url);

        }
    }
}

MainActivity

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    DatabaseReference database;
    MyAdapter myAdapter;
    ArrayList<ItemFirebase> list;
    Button view;
    TextView data;

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

        recyclerView = findViewById(R.id.materialList);
        view = findViewById(R.id.view);
        data = findViewById(R.id.url);
        database = FirebaseDatabase.getInstance().getReference("Items");
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        list = new ArrayList<>();
        myAdapter = new MyAdapter(this,list);
        recyclerView.setAdapter(myAdapter);

        database.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                for (DataSnapshot dataSnapshot : snapshot.getChildren()){

                    ItemFirebase itemFirebase = dataSnapshot.getValue(ItemFirebase.class);
                    list.add(itemFirebase);


                }
                myAdapter.notifyDataSetChanged();

            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

        view.setOnClickListener(view -> {
            Intent intent = new Intent(MainActivity.this, WebViewActivity.class);
            intent.putExtra("data", data.getText().toString());
            startActivity(intent);
            finish();
        });


    }
}

WebViewActivity

public class WebViewActivity extends AppCompatActivity {

    TextView url;
    WebView webView;

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

        url.findViewById(R.id.url);

        String data = getIntent().getStringExtra("data");

        webView = findViewById(R.id.webView);
        // включаем поддержку JavaScript
        webView.getSettings().setJavaScriptEnabled(true);
        // указываем страницу загрузки
        webView.loadUrl(url.getText().toString() + " " + data);

    }

}

There are no errors in the code itself, but when you try to open the application, it crashes
and shows an error indicating line 69 in MainActivity, the line itself view.setOnClickListener(view -> {

Error

Process: com.buratinoapps.newairdrop, PID: 18901
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.buratinoapps.newairdrop/com.buratinoapps.newairdrop.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

Answer 1

R.id.view is not in the markup.