Android findViewById在主Activity以外的类中使用时返回null

public class MainActivity extends AppCompatActivity {

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

        TextView textView = findViewById(R.id.textView);
        OtherClass otherClass = new OtherClass();
        otherClass.doSomething(textView);
    }
}

public class OtherClass {
    public void doSomething(TextView textView) {
        // 在这里可以使用textView
    }
}