我不了解Android中的Fragment生命周期，以及屏幕方向更改期间会发生什么。
我从Android SDK中的Master-Detail示例开始，我添加了以下代码行：
在MyItemListActivity我修改了onCreate()
public class MyItemListActivity extends FragmentActivity implements
MyItemListFragment.Callbacks {
/**
* Whether or not the activity is in two-pane mode, i.e. running on a tablet
* device.
*/
private boolean mTwoPane;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fragMgr = getSupportFragmentManager();
MyItemListFragment oldFragment = (MyItemListFragment)fragMgr.findFragmentByTag("booFragment");
if (null == oldFragment) {
FragmentTransaction xact = fragMgr.beginTransaction();
MyItemListFragment newFragment = MyItemListFragment.createInstance("boo");
xact.add(
R.id.myitem_list,
newFragment,
"booFragment");
xact.commit();
}
setContentView(R.layout.activity_myitem_list);
if (findViewById(R.id.myitem_detail_container) != null) {
// The detail container view will be present only in the
// large-screen layouts (res/values-large and
// res/values-sw600dp). If this view is present, then the
// activity should be in two-pane mode.
mTwoPane = true;
// In two-pane mode, list items should be given the
// 'activated' state when touched.
((MyItemListFragment) getSupportFragmentManager().findFragmentById(
R.id.myitem_list)).setActivateOnItemClick(true);
}
// TODO: If exposing deep links into your app, handle intents here.
}
/**
* Callback method from {@link MyItemListFragment.Callbacks} indicating that
* the item with the given ID was selected.
*/
@Override
public void onItemSelected(String id) {
if (mTwoPane) {
// In two-pane mode, show the detail view in this activity by
// adding or replacing the detail fragment using a
// fragment transaction.
Bundle arguments = new Bundle();
arguments.putString(MyItemDetailFragment.ARG_ITEM_ID, id);
MyItemDetailFragment fragment = new MyItemDetailFragment();
fragment.setArguments(arguments);
getSupportFragmentManager().beginTransaction()
.replace(R.id.myitem_detail_container, fragment).commit();
} else {
// In single-pane mode, simply start the detail activity
// for the selected item ID.
Intent detailIntent = new Intent(this, MyItemDetailActivity.class);
detailIntent.putExtra(MyItemDetailFragment.ARG_ITEM_ID, id);
startActivity(detailIntent);
}
}
}
在MyItemListFragment我创建了createInstance()
public class MyItemListFragment extends ListFragment {
/**
* The serialization (saved instance state) Bundle key representing the
* activated item position. Only used on tablets.
*/
private static final String STATE_ACTIVATED_POSITION = "activated_position";
/**
* The fragment's current callback object, which is notified of list item
* clicks.
*/
private Callbacks mCallbacks = sDummyCallbacks;
/**
* The current activated item position. Only used on tablets.
*/
private int mActivatedPosition = ListView.INVALID_POSITION;
/**
* A callback interface that all activities containing this fragment must
* implement. This mechanism allows activities to be notified of item
* selections.
*/
public interface Callbacks {
/**
* Callback for when an item has been selected.
*/
public void onItemSelected(String id);
}
/**
* A dummy implementation of the {@link Callbacks} interface that does
* nothing. Used only when this fragment is not attached to an activity.
*/
private static Callbacks sDummyCallbacks = new Callbacks() {
@Override
public void onItemSelected(String id) {
}
};
/**
* Mandatory empty constructor for the fragment manager to instantiate the
* fragment (e.g. upon screen orientation changes).
*/
public MyItemListFragment() {
}
public static MyItemListFragment createInstance(String boo) {
Bundle init = new Bundle();
init.putString(
"booboo",
boo);
MyItemListFragment frag = new MyItemListFragment();
frag.setArguments(init);
return frag;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// TODO: replace with a real list adapter.
setListAdapter(new ArrayAdapter<DummyContent.DummyItem>(getActivity(),
android.R.layout.simple_list_item_activated_1,
android.R.id.text1, DummyContent.ITEMS));
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Restore the previously serialized activated item position.
if (savedInstanceState != null
&& savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
setActivatedPosition(savedInstanceState
.getInt(STATE_ACTIVATED_POSITION));
}
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// Activities containing this fragment must implement its callbacks.
if (!(activity instanceof Callbacks)) {
throw new IllegalStateException(
"Activity must implement fragment's callbacks.");
}
mCallbacks = (Callbacks) activity;
}
@Override
public void onDetach() {
super.onDetach();
// Reset the active callbacks interface to the dummy implementation.
mCallbacks = sDummyCallbacks;
}
@Override
public void onListItemClick(ListView listView, View view, int position,
long id) {
super.onListItemClick(listView, view, position, id);
// Notify the active callbacks interface (the activity, if the
// fragment is attached to one) that an item has been selected.
mCallbacks.onItemSelected(DummyContent.ITEMS.get(position).id);
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
if (mActivatedPosition != ListView.INVALID_POSITION) {
// Serialize and persist the activated item position.
outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition);
}
}
/**
* Turns on activate-on-click mode. When this mode is on, list items will be
* given the 'activated' state when touched.
*/
public void setActivateOnItemClick(boolean activateOnItemClick) {
// When setting CHOICE_MODE_SINGLE, ListView will automatically
// give items the 'activated' state when touched.
getListView().setChoiceMode(
activateOnItemClick ? ListView.CHOICE_MODE_SINGLE
: ListView.CHOICE_MODE_NONE);
}
private void setActivatedPosition(int position) {
if (position == ListView.INVALID_POSITION) {
getListView().setItemChecked(mActivatedPosition, false);
} else {
getListView().setItemChecked(position, true);
}
mActivatedPosition = position;
}
}
应用程序在启动时运行正常，但是当我旋转屏幕时，应用程序崩溃，以下内容在日志中：
12-12 13：41：23.930：E / AndroidRuntime（31051）：java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.mymasterdetail / com.example.mymasterdetail.MyItemListActivity}：android.view。 InflateException：二进制XML文件行＃24：错误膨胀类片段
...
12-12 13：41：23.930：E / AndroidRuntime（31051）：引起：android.view.InflateException：二进制XML文件行＃24：错误膨胀类片段 12-12 13：41：23.930：E / AndroidRuntime（31051）：在android.view.LayoutInflater.createViewFromTag（LayoutInflater.java:713）
...
12-12 13：41：23.930：E / AndroidRuntime（31051）：at com.android.internal.policy.impl.PhoneWindow.setContentView（PhoneWindow.java:290） 12-12 13：41：23.930：E / AndroidRuntime（31051）：在android.app.Activity.setContentView（Activity.java:1928） 12-12 13：41：23.930：E / AndroidRuntime（31051）：at com.example.mymasterdetail.MyItemListActivity.onCreate（MyItemListActivity.java:52）
...
（第52行是对活动中setContentView()的调用。）
如果我删除xact.add()，那么该应用就可以运行了。 （但没有数据传递给Fragment。）
我知道FragmentTransaction方法将数据传递给我的Fragment是正确的，但是我没有看到我还需要做些什么来准备Fragment来处理与屏幕方向变化相关的生命周期事件，我不知道我知道如何给片段膨胀（隐式或明确地）。
（我正在使用平板电脑，所以我有两个显示器，以防万一。）
答案 0 :(得分：0)
尝试将setContentView（）移动到开始实例化片段之前。
如果先设置片段并尝试将它们附加到尚不存在的视图中，则可能会出现错误。
还要确保您的片段附加的视图存在于纵向和横向布局中。
在以编程方式添加片段时，请确保不要在XML布局中添加它们。您的布局中应该只有一个FrameLayout来将您的片段附加到。
答案 1 :(得分：0)
在方向更改期间发生的事情是当前活动被销毁并重新创建 - 这很有用，因为可以夸大替代布局（如果资源文件夹中有另一个布局用于另一个方向）。
可能在这里发生的事情是你试图在它被夸大之前访问一个片段（如Kuffs所说）。
答案 2 :(得分：0)
你的片段需要一个公共的空构造函数。
来自http://developer.android.com/reference/android/app/Fragment.html：
Fragment的所有子类都必须包含一个公共空构造函数。框架通常会在需要时重新实例化一个片段类，特别是在状态恢复期间，并且需要能够找到此构造函数来实例化它。如果空构造函数不可用，则在状态恢复期间的某些情况下将发生运行时异常。