java - SupportManager.getFragmentById 返回 null

Question

大家好，我一直被 id 返回 null 的 getFragment 困住了

xml文件

<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">

<FrameLayout
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
</FrameLayout>

<fragment
    android:id="@+id/navigation_drawer"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="left"
    tools:layout="@layout/fragment_navigation_drawer_list" />
</android.support.v4.widget.DrawerLayout>

主 Activity .java

public class MainActivity extends ActionBarActivity {
private static final String SCREEN_NAME = "MainActivity";

@Optional @InjectView(R.id.tool_bar) Toolbar toolbar;
//@InjectView(R.id.DrawerLayout) DrawerLayout mDrawerLayout;

@Inject GamerzWikiApplication mGamerzWikiApplication;
private NavigationDrawerFragment mNavigationDrawerFragment;

android.support.v7.app.ActionBar mActionBar;
ActionBarDrawerToggle mDrawerToggable;

private ArrayList<NavigationDrawerItem> mNavigationDrawerItemList;
private DrawerLayout mDrawerLayout;

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

    ButterKnife.inject(this);
    ObjectGraphInjector.inject(this);

    setSupportActionBar(toolbar);
    setupActionBar();
    setupDrawerLayout();

}


@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_main, menu);
    return true;
}

private void setupActionBar() {
    mActionBar = getSupportActionBar();

    //SetDisplayHomeAsUpEnabled => Set whether home should be displayed as an "up" affordance(objects action/ to perform).
    //mActionBar.setDisplayHomeAsUpEnabled(true);

    //Enable or disable the "home" button in the corner of the action bar.
    mActionBar.setHomeButtonEnabled(true);
}

private void setupDrawerLayout() {

    mNavigationDrawerItemList = new ArrayList<NavigationDrawerItem>();
    mNavigationDrawerItemList.add(new NavigationDrawerItem(getString(R.string.title_home), "{fa-home}") {
        @Override
        public void onClick() {
            mActionBar.setTitle(R.string.title_home);
            /*
            getSupportFragmentManager().beginTransaction()
                    .replace(R.id.container, new TopGameFragment())
                    .commit();
            */
        }
    });


    mNavigationDrawerItemList.add(new NavigationDrawerItem("ユーザ情報の確認・表示", "{fa-user}") {
        @Override
        public void onClick() {
            //startActivity(AccountSettingActivity.createIntent(getApplicationContext()));
        }
    });

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mNavigationDrawerFragment = (NavigationDrawerFragment)
            getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
    mNavigationDrawerFragment.setup(
            R.id.navigation_drawer,
            mNavigationDrawerItemList,
            mDrawerLayout
    );

    mActionBar.setTitle(R.string.title_home);
    /*
    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, new TopGameFragment())
            .commit();*/

}

@Override
public void onAttachFragment(Fragment fragment) {
    // TODO Auto-generated method stub
    super.onAttachFragment(fragment);

    Toast.makeText(getApplicationContext(), String.valueOf(fragment.getId()), Toast.LENGTH_SHORT).show();

}

@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);
}

这是在它引用的 logcat 中抛出的异常 mNavigationDrawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);

 Caused by: java.lang.NullPointerException
        at com.atfreaks.gamerzwiki.MainActivity.setupDrawerLayout(MainActivity.java:101)
        at com.atfreaks.gamerzwiki.MainActivity.onCreate(MainActivity.java:54)

我不知道它为什么返回 null 。谁能知道为什么会这样？谢谢!我包含了整个 mainActivity.java

Answer 1

我解决了我的问题。对于那些将来会遇到同样问题的人来说，这里就是解决方案。

问题不是因为 xml 文件或 getSupportManager.findFragmentById() 方法。通过一些调试，我尝试放置 if else 并检查 getSupportFragment 是否为 != null。

这是修复。

if(getSupportFragmentManager() != null){
        mNavigationDrawerFragment = (NavigationDrawerFragment)
                getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
        mNavigationDrawerFragment.setup(
                R.id.navigation_drawer,
                mNavigationDrawerItemList,
                mDrawerLayout
        );
    } else {
        Toast.makeText(getApplicationContext(), "getSupportFragmentManager is null", Toast.LENGTH_SHORT).show();
    }

也归功于@njzk2。