java - .java 代码中的 fragment 更改在哪里？

Question

我从 Android 开发人员那里下载了这个示例(它是一个抽屉导航)，由于我对 Android 开发非常陌生，所以我并不完全理解 fragment 。那么这段代码到底在哪里写了哪个 fragment 会改变以及哪个 fragment 将显示在屏幕上呢？

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

    mTitle = mDrawerTitle = getTitle();
    mPlanetTitles = getResources().getStringArray(R.array.planets_array);
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.left_drawer);
    mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
    mDrawerList.setAdapter(new ArrayAdapter<String>(this,
            R.layout.drawer_list_item, mPlanetTitles));
    mDrawerList.setOnItemClickListener(new DrawerItemClickListener());

    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(
            this,                  /* host Activity */
            mDrawerLayout,         /* DrawerLayout object */
            R.drawable.ic_drawer,  /* nav drawer image to replace 'Up' caret */
            R.string.drawer_open,  /* "open drawer" description for accessibility */
            R.string.drawer_close  /* "close drawer" description for accessibility */
            ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {
        selectItem(0);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    return super.onPrepareOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    switch(item.getItemId()) {
    default:
        return super.onOptionsItemSelected(item);
    }
}

private class DrawerItemClickListener implements ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        selectItem(position);
    }
}

private void selectItem(int position) {
    Fragment fragment = new PlanetFragment();
    Bundle args = new Bundle();
    args.putInt(PlanetFragment.ARG_PLANET_NUMBER, position);
    fragment.setArguments(args);

    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

    mDrawerList.setItemChecked(position, true);
    setTitle(mPlanetTitles[position]);
    mDrawerLayout.closeDrawer(mDrawerList);
}

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    getActionBar().setTitle(mTitle);
}

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    mDrawerToggle.onConfigurationChanged(newConfig);
}

public static class PlanetFragment extends Fragment {
    public static final String ARG_PLANET_NUMBER = "planet_number";
    public PlanetFragment() {
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_planet, container, false);
        int i = getArguments().getInt(ARG_PLANET_NUMBER);
        String planet = getResources().getStringArray(R.array.planets_array)[i];

        int imageId = getResources().getIdentifier(planet.toLowerCase(Locale.getDefault()),
                        "drawable", getActivity().getPackageName());
        ((ImageView) rootView.findViewById(R.id.image)).setImageResource(imageId);
        getActivity().setTitle(planet);
        return rootView;
    }
}

Answer 1

这部分代码:

FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

负责更改 fragment 。正如您所看到的，添加或替换 fragment 等操作发生在名为 FragmentTransaction 的对象上，该方法 beginTransaction 返回。

replace 方法用作为第二个参数给出的 fragment 替换作为第一个参数给出的容器中的内容。

方法提交只是安排此事务的提交。

了解更多信息here .

如果您不确定方法链接是什么，请阅读 here.