将 Activity 转换为 Fragment

Question

我是 Android 新手，我正在尝试将 Activity 转换为 Fragment，但我不知道如何解决错误。

当我将其更改为Fragment 时，我会收到很多红色代码setContentView、findViewById 和getMenuInflater。我知道这些可能是红色的，因为它们是用于Activities，但我不确定它们是什么意思。

    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.LinearLayoutManager;
    import android.support.v7.widget.RecyclerView;
    import android.view.Menu;
    import android.view.MenuItem;

    public class LocationsFragment extends Fragment {

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    RecyclerView.Adapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_card_demo);
        // Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        // setSupportActionBar(toolbar);

        recyclerView =
                (RecyclerView) findViewById(R.id.recycler_view);

        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        adapter = new RecyclerAdapter();
        recyclerView.setAdapter(adapter);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_card_demo, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Answer 1

setContentView()

Fragments 中没有这样的方法。相反，您覆盖onCreateView() 并从中返回一些视图。您可以使用传入的LayoutInflater 来扩充您通常传递给setContentView() 的布局ID，然后将其返回。

findViewById()

片段没有findViewById() 方法。但是，在onCreateView() 返回后的任何时间，您都可以改用getView().findViewById()。在onCreateView() 内部，如果您将膨胀视图命名为root，则可以调用root.findViewById()。在onCreateView() 之前，无法查找任何视图（因为它们还没有被夸大）。

getMenuInflater()

片段对onCreateOptionsMenu() 使用不同的签名。它看起来像这样：

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    // ...
}

您可以使用传入的MenuInflater 而不是调用getMenuInflater()。

---

把所有这些放在一起，这就是你所拥有的：

public class LocationsFragment extends Fragment {

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    RecyclerView.Adapter adapter;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.activity_card_demo, container, false);

        recyclerView = (RecyclerView) root.findViewById(R.id.recycler_view);

        layoutManager = new LinearLayoutManager(getContext());
        recyclerView.setLayoutManager(layoutManager);

        adapter = new RecyclerAdapter();
        recyclerView.setAdapter(adapter);

        return root;
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        inflater.inflate(R.menu.menu_card_demo, menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}