从主要活动中打开MultipleFragment

Question

我使用MultipleFragment类扩展Fragment。 我想从MainActivity打开此片段。 为此，我使用MultipleFragment myfragment的实例：

MultipleFragment myfragment = new MultipleFragment();
            myfragmentTransaction.replace(R.id.fragment_multiple_list_view , myfragment).commit();

我得到一个错误，认为“ myfragment”参数应为Fragment类型。

错误：不兼容的类型：MultipleFragment无法转换为片段myfragmentTransaction.replace（R.id.fragment_multiple_list_view，myfragment）.commit（）;

但是MultipleFragment扩展了Fragment ...正确的做法是什么？ 如何使函数在其参数中识别扩展类的类型？

public class MainActivity extends AppCompatActivity {

    private Button btnFragment;

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

        btnFragment = (Button)findViewById(R.id.btnFragment);
        btnFragment.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentManager myfragmentManager = getFragmentManager ();
                FragmentTransaction myfragmentTransaction = myfragmentManager.beginTransaction ();
                MultipleFragment myfragment = new MultipleFragment();
                myfragmentTransaction.replace(R.id.fragment_multiple_list_view , myfragment).commit();

            }
        });
    }
}

public class MultipleFragment extends Fragment implements  AdapterView.OnItemClickListener {

    MultipleAdapter mAdapter;

    public MultipleFragment() {
        // Required empty public constructor
    }

    public static MultipleFragment newInstance() {
        return new MultipleFragment();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_multiple, container, false);
        ListView listView = (ListView) view.findViewById(R.id.fragment_multiple_list_view);

        MultipleData android = new MultipleData("Android", false);
        MultipleData iPhone = new MultipleData("iPhone", false);
        MultipleData windowsMobile = new MultipleData("WindowsMobile", false);

        MultipleData blackberry = new MultipleData("Blackberry", false);
        MultipleData webOS = new MultipleData("WebOS", false);
        MultipleData ubuntu = new MultipleData("Ubuntu", false);

        MultipleData windows7 = new MultipleData("Windows7", false);
        MultipleData max = new MultipleData("Max OS X", false);
        MultipleData linux = new MultipleData("Linux", false);

        MultipleData os = new MultipleData("OS/2", false);
        MultipleData symbian = new MultipleData("Symbian", false);

        List<MultipleData> list = new ArrayList<>();
        list.add(0, android);
        list.add(1, iPhone);
        list.add(2, windowsMobile);

        list.add(3, blackberry);
        list.add(4, webOS);
        list.add(5, ubuntu);

        list.add(6, windows7);
        list.add(7, max);
        list.add(8, linux);

        list.add(9, os);
        list.add(10, symbian);

        mAdapter = new MultipleAdapter(getActivity(),list);
        listView.setAdapter(mAdapter);
        listView.setOnItemClickListener(this);
        return view;
    }

    @Override
    public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
        mAdapter.setSelectedIndex(position);
        mAdapter.notifyDataSetChanged();
    }
}

Answer 1

您应该使用getSupportFragmentManager() ，而不是getFragmentManager() 。

FragmentManager myfragmentManager = getSupportFragmentManager()

不建议使用Fragments框架（ android.app.Fragment ， android.app.FragmentManager ），而应该使用Support Library / AndroidX版本。

Answer 2

检查您是否混用了android.support.v4.app.Fragment和android.app.Fragment。 您需要转换所有用途以使用支持库，这也意味着调用getSupportFragmentManager（）。

例如：

 android.support.v4.app.FragmentManager myfragmentManager = getSupportFragmentManager();

android.support.v4.app.FragmentTransaction myfragmentTransaction = myfragmentManager.beginTransaction();

 MultipleFragment myfragment = new MultipleFragment();

myfragmentTransaction.replace(R.id.fragment_multiple_list_view, myfragment);

myfragmentTransaction.commit();