（新手小问题）OnClickListener报空指针异常

Question

指针OnClickListener

Answer 1

可能是R.java生成的问题，你清理一下项目试试：Project-Clean菜单

Answer 2

因为fragment里面是不能在oncreate里面绑定id，应该在oncreateView里面绑定ID

Answer 3

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
         
        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction()
                    .add(R.id.container, new PlaceholderFragment())
                    .commit();
        }
                //用rootView来装载你的fragment布局，然后在该布局上才能找到你的Button
        View rootView =LayoutInflater.from(this).inflate(R.layout.fragment_main, null); 
        bt=(Button)rootView.findViewById(R.id.button);
        bt.setOnClickListener(new OnClickListener() {
             
            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub
                System.out.println("dear");
            }
        });
    }

Answer 4

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
View rootView = inflater.inflate(R.layout.activity_main, container, false);
                bt=(Button)rootView.findViewById(R.id.button);
            bt.setOnClickListener(new OnClickListener() {
                  
                @Override
                public void onClick(View arg0) {
                    // TODO Auto-generated method stub
                    System.out.println("dear");
                }
            });
return rootView;
}