setText is shown in red and i don't undrestand why

Question

setText is shown in red and i don't undrestand why

public class MainActivity extends AppCompatActivity {

    TextView v = (TextView)findViewById(R.id.textInput);
    Button b = (Button)findViewById(R.id.btn12);
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        b.setOnClickListener((new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                v.setText("aaa");// why setText not found
            }
        }));


    }

}

thx

Answer 1

Move these methods:

TextView v = (TextView)findViewById(R.id.textInput);
Button b = (Button)findViewById(R.id.btn12);

You can use:

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TextView v = (TextView)findViewById(R.id.textInput);
    Button b = (Button)findViewById(R.id.btn12);
    b.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View view) {
            v.setText("aaa");// why setText not found
        }
    });

or you can use:

public class MainActivity extends AppCompatActivity {

    private TextView v;
    private Button b;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        v = (TextView)findViewById(R.id.textInput);
        b = (Button)findViewById(R.id.btn12);
        b.setOnClickListener(new View.OnClickListener(){
           @Override
           public void onClick(View view) {
            v.setText("aaa");// why setText not found
           }
        });

    }

}