Question

我基本上遇到与OP完全相同的问题：How to change fragments using Android navigation drawer

在Android Studio中使用模板进行导航抽屉活动。

我尝试了Dreagan的回答，但我现在陷入了一段错误。

这是我的代码

import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.ArrayAdapter;
import android.widget.TextView;


public   class MainActivity extends Activity
        implements NavigationDrawerFragment.NavigationDrawerCallbacks {

    /**
     * Fragment managing the behaviors, interactions and presentation of the navigation drawer.
     */
    private NavigationDrawerFragment mNavigationDrawerFragment;

    /**
     * Used to store the last screen title. For use in {@link #restoreActionBar()}.
     */
    private CharSequence mTitle;

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

        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getFragmentManager().findFragmentById(R.id.navigation_drawer);
        mTitle = getTitle();

        // Set up the drawer.
        mNavigationDrawerFragment.setUp(
                R.id.navigation_drawer,
                (DrawerLayout) findViewById(R.id.drawer_layout));
    }

    @Override
    public void onNavigationDrawerItemSelected(int position) {
        // update the main content by replacing fragments

        Fragment fragment = new NewsfeedFragment();
        FragmentManager fragmentManager = getFragmentManager();

        Bundle args = new Bundle();
        args.putInt(NewsfeedFragment.ARG_PLANET_NUMBER, position);
        fragment.setArguments(args);

        switch(position){
            case 0:
                fragment = new NewsfeedFragment();

                break;

            case 1:
                fragment = new NewsfeedFragment();
                break;
        }
        fragmentManager.beginTransaction()
                .replace(R.id.container, fragment)
                .commit();
    }

    public void onSectionAttached(int number) {

        switch (number) {
            case 1:
                mTitle = getString(R.string.title_section1);
                break;

            case 2:
                mTitle = getString(R.string.title_section2);
                break;

            case 3:
                mTitle = getString(R.string.title_section3);
                break;
        }
    }

    public void restoreActionBar() {
        ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
        actionBar.setDisplayShowTitleEnabled(true);
        actionBar.setTitle(mTitle);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (!mNavigationDrawerFragment.isDrawerOpen()) {
            // Only show items in the action bar relevant to this screen
            // if the drawer is not showing. Otherwise, let the drawer
            // decide what to show in the action bar.
            getMenuInflater().inflate(R.menu.main, menu);
            restoreActionBar();
            return true;
        }
        return super.onCreateOptionsMenu(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);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            return rootView;
        }

        @Override
        public void onAttach(Activity activity) {
            super.onAttach(activity);
            ((MainActivity) activity).onSectionAttached(
                    getArguments().getInt(ARG_SECTION_NUMBER));
        }
    }

}

如果我在这里运行代码，我会收到以下错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{dk.gruppe2.jammerbugtevent/dk.gruppe2.jammerbugtevent.MainActivity}: java.lang.ClassCastException: dk.gruppe2.jammerbugtevent.MainActivity@429e4a70 must implement OnFragmentInteractionListener

当我实施OnFragmentInteractionListener时，我收到以下错误：

Error:(22, 9) error: MainActivity is not abstract and does not override abstract method onFragmentInteraction(Uri) in OnFragmentInteractionListener

当我将MainActivity声明为抽象时，我收到此错误：

    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{dk.gruppe2.jammerbugtevent/dk.gruppe2.jammerbugtevent.MainActivity}: java.lang.InstantiationException: can't instantiate class dk.gruppe2.jammerbugtevent.MainActivity

我是android的新手，并不是一个关于编程的专家。任何帮助将非常感激。在此先感谢。

Answer 1

Here是对事情的解释！

读取代码我没有看到任何类转换异常...您正在将您的活动转换为OnFragmentInteractionListener接口。也许在其中一个片段中。

此外：

当我实现OnFragmentInteractionListener时，我得到以下内容   错误：

错误：（22,9）错误：MainActivity不是抽象的，也不是   覆盖onFragmentInteraction（Uri）中的抽象方法   OnFragmentInteractionListener

实现OnFragmentInteractionListener时，还必须覆盖方法：onFragmentInteraction（Uri）。

Answer 2

看起来你没有正确设置片段：

@Override
    public void onNavigationDrawerItemSelected(int position) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        switch(position)
        {
            case 0:
                fragmentManager.beginTransaction()
                        .replace(R.id.container, MainListFragment.newInstance())
                        .commit();
                break;
            case 1:
                fragmentManager.beginTransaction()
                        .replace(R.id.container, Fragment2.newInstance())
                        .commit();
            case 2:
                fragmentManager.beginTransaction()
                        .replace(R.id.container, Fragment3.newInstance())
                        .commit();
                break;
        }

    }

尝试使用此格式，您不会使用您在片段中定义的新实例方法。

Answer 3

我发现我只实现了接口，但仍然需要从接口

实现这些方法

从导航抽屉更改片段

3 个答案: