Java 如何参加特定的活动？

我的应用程序是如何构造的

Class A extends Activity {
    Button cButton = (Button) findViewById(...);
    Button dButton = (Button) findViewById(...);

    //invoked when cButton is clicked
    methodButtonC() { 
        //Here I want to go to the activity of class C and this is how I have tried to solve it...  
        Intent intent = new Intent(A.this, C.class);
        startActivity(intent);
    }
    //invoked when dButton is clicked
    methodButtonD() { 
         //Same problem as above but with Class D
    }
} 

// Base Class for C & D, No real purpose except sharing som methods to C & D (should probobly be abstract?)
Class B extends A {  
    // vairables and methods for inheritance
} 

Class C extends B {
    // uses derived methods and variables from Class B
}

Class D extends B {
    // uses derived methods and variables from Class B
}

---

当我运行应用程序并单击按钮C或D时，会发生错误。我该怎么做呢？

我认为您必须先通过调用setContentView（…）覆盖onCreate并从xml加载视图，然后再尝试使用findViewById（…）查找按钮

@创建时重写公共void（Bundle savedInstanceState）
{
super.onCreate（savedInstanceState）；
setContentView（右布局）；
buttonX=findViewById（…）；
}
AndroidManifest.xml
中是否提到了您的所有活动？发生了什么错误？至少给我们这么多。很可能它说明了你做错了什么。给你的按钮起一个和你的类相同的名字对我来说有点困惑。是的，每个活动都在AndroidManifest.xml 2中。错误为nullPointerException
@Override public void onCreate(Bundle savedInstanceState) 
{
  super.onCreate(savedInstanceState);
  setContentView(R.layout.<yourview>);

  buttonX = findViewById (...);
}