如何在 Android Studio 的 MainActivity 中不使用构造函数？

Question

I'm a beginner. I'm trying to make Locale project with Android Studio. So I made a class regard with Context. In MainActivity required a constructor. But, I'm heard that MainActivity do not need constructor but onCreate.

Here is my code.

BaseContextWrapper

    public class BaseContextWrapper extends AppCompatActivity {
    //AppCompatActivity-FragmentActivity-ComponentActivity-Activity-ContextThemeWrapper-ContextWrapper-Context
    public BaseContextWrapper(Context base) {
        super.attachBaseContext(base);
    }

    @RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN_MR1)
    @NonNull
    public static ContextWrapper wrap(Context context) {
        Resources resources = context.getResources();
        Configuration newConfig = new Configuration();
        DisplayMetrics metrics = resources.getDisplayMetrics();
        newConfig.setToDefaults();

        newConfig.densityDpi = metrics.densityDpi;
        if (Build.VERSION.SDK_INT > Build.VERSION_CODES.JELLY_BEAN_MR1) {
            context = context.createConfigurationContext(newConfig);
        } else {
            resources.updateConfiguration(newConfig, resources.getDisplayMetrics());
        }
        return new BaseContextWrapper(context);
    }
}

MainActivity

    public class MainActivity extends BaseContextWrapper {
    public MainActivity(Context base) {
        super(base);
    }

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

Answer 1

It all depends on what you inherit from. If from "extends Base ContextWrapper", then the constructor is required, it is included in the class. But if from "extends AppCompatActivity" then nothing but the onCreate() method is needed

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

Answer 2

Rewrite your MainActivity as

public class MainActivity extends AppCompatActivity {
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}