我遇到这个奇怪的问题,我的列表片段创建了两次,一次是在父活动上调用super.oncreate时,一次是在同一父活动上调用setContentView时。这是一个简单的应用程序,我使用不同的布局进行纵向和横向。
以下是主要活动:
private HeadlinesFragment headlines;
@Override
public void onCreate(Bundle savedInstanceState) {
Log.w("MainActivity", "Before super.onCreate: " + this.toString());
super.onCreate(savedInstanceState);
Log.w("MainActivity", "Before setContentView: " + this.toString());
setContentView(R.layout.news_articles);
//check to see if its portrait
if (findViewById(R.id.fragment_container) != null) {
if(getSupportFragmentManager().findFragmentById(R.id.fragment_container) == null) {
headlines = new HeadlinesFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, headlines).commit();
}
}
}
这是layout-land文件夹中的news_articles:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent">
<fragment android:name="com.example.android.fragments.HeadlinesFragment"
android:id="@+id/headlines_fragment"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="match_parent" />
<fragment android:name="com.example.android.fragments.ArticleFragment"
android:id="@+id/article_fragment"
android:layout_weight="2"
android:layout_width="0dp"
android:layout_height="match_parent" />
这是布局文件夹中的news_articles(纵向方向)
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
这里是两次创建的headlinesfragment
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// The container Activity must implement this interface so the frag can deliver messages
public interface OnHeadlineSelectedListener {
/** Called by HeadlinesFragment when a list item is selected */
public void onArticleSelected(int position);
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.w("HeadlinesFragment", "inside onCreate: " + this.toString());
// We need to use a different list item layout for devices older than Honeycomb
int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;
// Create an array adapter for the list view, using the Ipsum headlines array
setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines));
}
@Override
public void onStart() {
super.onStart();
// When in landscape layout, set the listview to highlight the selected list item
// (We do this during onStart because at the point the listview is available.)
if (getFragmentManager().findFragmentById(R.id.article_fragment) != null) {
getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
}
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception.
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
// TODO Auto-generated method stub
super.onCreateOptionsMenu(menu, inflater);
}
@Override
public void onDestroy() {
Log.w("HeadlinesFragment", "inside onDestroy: " + this.toString());
super.onDestroy();
}
}
这是articlefragment
public class ArticleFragment extends Fragment {
final static String ARG_POSITION = "position";
int mCurrentPosition = 0;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Log.w("ArticleFragment", "inside onCreateView: " + this.toString());
if (savedInstanceState != null) {
mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
}
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.article_view, container, false);
return view;
}
@Override
public void onStart() {
super.onStart();
Bundle args = getArguments();
if (args != null) {
// Set article based on argument passed in
updateArticleView(args.getInt(ARG_POSITION));
} else if (mCurrentPosition != -1) {
// Set article based on saved instance state defined during onCreateView
updateArticleView(mCurrentPosition);
}
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Save the current article selection in case we need to recreate the fragment
outState.putInt(ARG_POSITION, mCurrentPosition);
}
@Override
public void onDestroy() {
Log.w("ArticleFragment", "inside onDestroy: " + this.toString());
super.onDestroy();
}
}
详细问题是:
1)以纵向方向启动应用程序 2)调用setContentView并加载news_articles,但是它是带有fragment_container的那个。 3)创建headlinesfragment //到目前为止正常行为 4)改变方向为景观 5)mainActivity被破坏 - &gt; headlinefragment被摧毁 6)调用super.oncreate on mainactivity 7)创建标题碎片 8)调用mainactivity的setcontentview 9)创建另一个headlinefragment //问题
我已经放置了日志,如上面的代码所示,这是我在纵向模式下启动应用程序时的输出,然后我更改为横向。
W/MainActivity(6925): Before super.onCreate: MainActivity@41d81238
W/MainActivity(6925): Before setContentView: MainActivity@41d81238
W/HeadlinesFragment(6925): inside onCreate: HeadlinesFragment{41d8d4d8 #0 id=0x7f050001}
W/MainActivity(6925): inside onDestroy: MainActivity@41d81238
W/HeadlinesFragment(6925): inside onDestroy: HeadlinesFragment{41d8d4d8 # 0id=0x7f050001}
W/MainActivity(6925): Before super.onCreate: MainActivity@41ea6258
W/HeadlinesFragment(6925): inside onCreate: HeadlinesFragment{41ea7290 #0 id=0x7f050001}
W/MainActivity(6925): Before setContentView: MainActivity@41ea6258
W/HeadlinesFragment(6925): inside onCreate: HeadlinesFragment{41eb1f30 #1 id=0x7f050002}
W/ArticleFragment(6925): inside onCreateView: ArticleFragment{41eb5f20 #2 id=0x7f050003}
我希望我已经清楚了解我的代码和日志,在我看来super.oncreate和setcontentview都创建了一个headlinesfragment;至少我认为。
我的问题是为什么要创建2个headlinesfragment实例以及如何避免这种情况。
非常感谢您对此有任何帮助
答案 0 :(得分:17)
在您的活动的onCreate
中,您可以查看savedInstanceState
捆绑包的状态。如果它不为空,则表示发生了配置更改(在您的情况下,屏幕方向更改),并且您无需重新创建Fragment
。
您正在做的另一个错误是您尝试使用Fragment
检索findFragmentById
。你没有传递Fragment id,而是给它附加到Fragment的View的id,这是不同的(这就是为什么我猜这总是返回null)。
正确的实现更像是这个(这是你的Activity
):
//check to see if its portrait
if (findViewById(R.id.fragment_container) != null) {
if(savedInstanceState == null) {
headlines = new HeadlinesFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, headlines, FRAGMENT_TAG_STRING).commit(); // Use tags, it's simpler to deal with
} else {
headlines = getSupportFragmentManager().findFragmentByTag(FRAGMENT_TAG_STRING);
}
}
答案 1 :(得分:2)
覆盖onSavedInstanceState而不调用它超级。