片段中的 RecyclerView 在设备屏幕旋转时崩溃
RecyclerView in a Fragment crashes on device screen rotation
我发现很多问题都不符合我的情况。
我有一个 Activity 包含一个 Fragment，其中有一个 RecyclerView 和一个用于管理 CardView 对象的适配器。
MainActivity.java
private static final String MENU_OPENED = "menu_is_opened";
// For toolbar
private Toolbar toolbar;
// For sliding menu
private DrawerLayout mDrawerLayout;
private ListFragment navMenuFragment;
private ArrayAdapter<String> adapter;
private ArrayList<String> menuList;
private ActionBarDrawerToggle mDrawerToggle;
private boolean menuIsOpened;
//For recyclerview
private RecyclerViewFragment recyclerViewFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("MAIN_ACTIVITY: ", "onCreate");
setContentView(R.layout.activity_main);
menuIsOpened = false;
initToolbar();
initDrawer();
initSlidingMenu();
initRecyclerView();
// If an instance of this activity had previously stopped, we can // get the original text it started with.
if(savedInstanceState!= null)
{
// Restore values!
menuIsOpened = savedInstanceState.getBoolean(MENU_OPENED);
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Log.d("MAIN_ACTIVITY: ", "onSaveInstanceState");
outState.putBoolean(MENU_OPENED, menuIsOpened);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_toolbar, menu); // Inflates action items
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
return super.onPrepareOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
switch (item.getItemId())
{
case (R.id.searchGroup):
Log.d("PRESSED Menu Item: ", (String) item.getTitle());
Toast.makeText(this, "searchGroup selected!", Toast.LENGTH_SHORT).show();
break;
case (R.id.addGroup):
Log.d("PRESSED Menu Item: ", (String) item.getTitle());
Toast.makeText(this, "addGroup selected!", Toast.LENGTH_SHORT).show();
break;
default: return true;
}
return true;
}
@Override
public void onClick(View v) // Intercept Navigation Button's click
{
Toast.makeText(this, "Nav.butt. selected!", Toast.LENGTH_SHORT).show();
}
private void initToolbar()
{
toolbar = (Toolbar) findViewById(R.id.myToolbar);
if (toolbar != null)
{
setSupportActionBar(toolbar); // set toolbar as the new Action Bar
toolbar.setNavigationIcon(R.drawable.ic_menu);
toolbar.setNavigationOnClickListener(this); // Avoid to do "new"
getSupportActionBar().setDisplayShowTitleEnabled(false);
// Deletes the activity Label ( don't put it after setTitle! )
toolbar.setTitle(R.string.toolbarTitle);
}
}
private void initSlidingMenu()
{
FragmentManager fm = getFragmentManager();
navMenuFragment = (ListFragment) fm.findFragmentById(R.id.navigation_menu_fragment);
if(adapter == null || menuList == null)
{
menuList = new ArrayList<String>();
menuList.add("Map");
menuList.add("List");
menuList.add("Profile");
adapter = new ArrayAdapter<String>(this,
R.layout.fragment_navigation_drawer,
menuList);
navMenuFragment.setListAdapter(adapter);
navMenuFragment.getView().setBackgroundColor(Color.DKGRAY);
}
}
private void initDrawer(){
if(toolbar == null) initToolbar();
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
toolbar, R.string.drawer_open, R.string.drawer_close) {
/** Called when a drawer has settled in a completely closed state. */
public void onDrawerClosed(View view) {
super.onDrawerClosed(view);
menuIsOpened = false;
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
/** Called when a drawer has settled in a completely open state. */
public void onDrawerOpened(View drawerView) {
super.onDrawerOpened(drawerView);
menuIsOpened = true;
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
}
private void initRecyclerView(){
if (recyclerViewFragment == null){
recyclerViewFragment = new RecyclerViewFragment();
}
// Add recyclerViewFragment to Activity
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.id.fragments_container, recyclerViewFragment); // calls onInflate() ecc
ft.commit();
}
你需要关注的方法是initRecyclingView和onCreate()。
然后我有一个
RecyclerViewFragment.java
public class RecyclerViewFragment extends Fragment {
private static final String BUNDLE_RECYCLER_VIEW_FRAGMENT_LAYOUT = "bundle.recycler.view.fragment.layout";
private RecyclerView mRecyclerView;
private RecyclerView.LayoutManager mLayoutManager;
public RecyclerViewFragment(){
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Log.d("RECYCLER_VIEW_FRAGM: ", "onCreateView");
return inflater.inflate(R.layout.fragment_recycler, container, false);
}
/* From Docs: Called after Activity.OnCreate has been completed by the hosting Activity.
* Final tweaks to the user interface should be performed at this time.
*/
@Override
public void onActivityCreated(Bundle savedInstanceState) {
Log.d("RECYCLER_VIEW_FRAGM: ", "onActivityCreated");
super.onActivityCreated(savedInstanceState);
// I know that the recyclerView has been instantiated ( look at onCreateView() )
mRecyclerView = (RecyclerView) getActivity().findViewById(R.id.my_recycler_view);
/* use this setting to improve performance if you know that changes
* in content do not change the layout size of the RecyclerView
*/
//mRecyclerView.setHasFixedSize(true);
// using a linear layout manager as doc suggest
mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);
ArrayList<Group> al = new ArrayList<>();
Group g = new Group("My First Group", R.drawable.ic_group_icon);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
// specify an adapter
Adapter recyclerViewAdapter = new RecyclerViewAdapter(al);
mRecyclerView.setAdapter(recyclerViewAdapter);
}
最后我遇到了两个问题：
1) 当我旋转屏幕时，出现以下异常：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.onMeasure(android.support.v7.widget.RecyclerView$Recycler, android.support.v7.widget.RecyclerView$State, int, int)' on a null object reference
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
at android.view.View.measure(View.java:17547)
2) 查看日志输出，似乎我的 Fragment 没有与 Activity 一起被销毁（如果我没记错的话，屏幕的旋转会破坏 activity 并开始一个新的）。
我想找到第 1 点的解决方案，但如果你能给我建议第 2 点的东西就更好了。
谢谢。 （请询问您是否需要更多代码，例如xml个文件）
将 onActivityCreated() 中的代码移至 onViewCreated() 中。在轮换时，您的 RecyclerView 可能会在 onActivityCreated() 回调被调用（您设置 LayoutManager 的位置）之前布局。
// I know that the recyclerView has been instantiated ( look at onCreateView() )
mRecyclerView = (RecyclerView) getActivity().findViewById(R.id.my_recycler_view);
您肯定不在 Fragment 中使用它。要在 Fragment 中获取视图，请将其放在 onCreateView 或 onViewCreated 中。你有你的片段的根视图实例，然后使用 View childView = rootView.findViewById(someId) 代替。
我很惊讶你只在方向改变时得到这个错误。您的 RecyclerView 需要正确设置 LayoutManager 才能正常工作。问题是您在 Activity 中创建了 RecyclerView，但在 Fragment 中对其进行了初始化，并且片段通常是异步添加或初始化的，这意味着在某些情况下 Activity 将尝试在执行位于 Fragment 中的初始化代码之前显示 RecyclerView。
RecyclerView 及其初始化代码应位于同一容器中：Activity 或 Fragment。避免从 Activity 访问 Fragment 视图或从 Fragment.
访问 Activity 视图
我发现很多问题都不符合我的情况。
我有一个 Activity 包含一个 Fragment，其中有一个 RecyclerView 和一个用于管理 CardView 对象的适配器。
MainActivity.java
private static final String MENU_OPENED = "menu_is_opened";
// For toolbar
private Toolbar toolbar;
// For sliding menu
private DrawerLayout mDrawerLayout;
private ListFragment navMenuFragment;
private ArrayAdapter<String> adapter;
private ArrayList<String> menuList;
private ActionBarDrawerToggle mDrawerToggle;
private boolean menuIsOpened;
//For recyclerview
private RecyclerViewFragment recyclerViewFragment;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("MAIN_ACTIVITY: ", "onCreate");
setContentView(R.layout.activity_main);
menuIsOpened = false;
initToolbar();
initDrawer();
initSlidingMenu();
initRecyclerView();
// If an instance of this activity had previously stopped, we can // get the original text it started with.
if(savedInstanceState!= null)
{
// Restore values!
menuIsOpened = savedInstanceState.getBoolean(MENU_OPENED);
}
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Log.d("MAIN_ACTIVITY: ", "onSaveInstanceState");
outState.putBoolean(MENU_OPENED, menuIsOpened);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_toolbar, menu); // Inflates action items
return true;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
return super.onPrepareOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
switch (item.getItemId())
{
case (R.id.searchGroup):
Log.d("PRESSED Menu Item: ", (String) item.getTitle());
Toast.makeText(this, "searchGroup selected!", Toast.LENGTH_SHORT).show();
break;
case (R.id.addGroup):
Log.d("PRESSED Menu Item: ", (String) item.getTitle());
Toast.makeText(this, "addGroup selected!", Toast.LENGTH_SHORT).show();
break;
default: return true;
}
return true;
}
@Override
public void onClick(View v) // Intercept Navigation Button's click
{
Toast.makeText(this, "Nav.butt. selected!", Toast.LENGTH_SHORT).show();
}
private void initToolbar()
{
toolbar = (Toolbar) findViewById(R.id.myToolbar);
if (toolbar != null)
{
setSupportActionBar(toolbar); // set toolbar as the new Action Bar
toolbar.setNavigationIcon(R.drawable.ic_menu);
toolbar.setNavigationOnClickListener(this); // Avoid to do "new"
getSupportActionBar().setDisplayShowTitleEnabled(false);
// Deletes the activity Label ( don't put it after setTitle! )
toolbar.setTitle(R.string.toolbarTitle);
}
}
private void initSlidingMenu()
{
FragmentManager fm = getFragmentManager();
navMenuFragment = (ListFragment) fm.findFragmentById(R.id.navigation_menu_fragment);
if(adapter == null || menuList == null)
{
menuList = new ArrayList<String>();
menuList.add("Map");
menuList.add("List");
menuList.add("Profile");
adapter = new ArrayAdapter<String>(this,
R.layout.fragment_navigation_drawer,
menuList);
navMenuFragment.setListAdapter(adapter);
navMenuFragment.getView().setBackgroundColor(Color.DKGRAY);
}
}
private void initDrawer(){
if(toolbar == null) initToolbar();
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
toolbar, R.string.drawer_open, R.string.drawer_close) {
/** Called when a drawer has settled in a completely closed state. */
public void onDrawerClosed(View view) {
super.onDrawerClosed(view);
menuIsOpened = false;
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
/** Called when a drawer has settled in a completely open state. */
public void onDrawerOpened(View drawerView) {
super.onDrawerOpened(drawerView);
menuIsOpened = true;
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
}
private void initRecyclerView(){
if (recyclerViewFragment == null){
recyclerViewFragment = new RecyclerViewFragment();
}
// Add recyclerViewFragment to Activity
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.id.fragments_container, recyclerViewFragment); // calls onInflate() ecc
ft.commit();
}
你需要关注的方法是initRecyclingView和onCreate()。 然后我有一个 RecyclerViewFragment.java
public class RecyclerViewFragment extends Fragment {
private static final String BUNDLE_RECYCLER_VIEW_FRAGMENT_LAYOUT = "bundle.recycler.view.fragment.layout";
private RecyclerView mRecyclerView;
private RecyclerView.LayoutManager mLayoutManager;
public RecyclerViewFragment(){
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
Log.d("RECYCLER_VIEW_FRAGM: ", "onCreateView");
return inflater.inflate(R.layout.fragment_recycler, container, false);
}
/* From Docs: Called after Activity.OnCreate has been completed by the hosting Activity.
* Final tweaks to the user interface should be performed at this time.
*/
@Override
public void onActivityCreated(Bundle savedInstanceState) {
Log.d("RECYCLER_VIEW_FRAGM: ", "onActivityCreated");
super.onActivityCreated(savedInstanceState);
// I know that the recyclerView has been instantiated ( look at onCreateView() )
mRecyclerView = (RecyclerView) getActivity().findViewById(R.id.my_recycler_view);
/* use this setting to improve performance if you know that changes
* in content do not change the layout size of the RecyclerView
*/
//mRecyclerView.setHasFixedSize(true);
// using a linear layout manager as doc suggest
mLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(mLayoutManager);
ArrayList<Group> al = new ArrayList<>();
Group g = new Group("My First Group", R.drawable.ic_group_icon);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
al.add(g);
// specify an adapter
Adapter recyclerViewAdapter = new RecyclerViewAdapter(al);
mRecyclerView.setAdapter(recyclerViewAdapter);
}
最后我遇到了两个问题：
1) 当我旋转屏幕时，出现以下异常：
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView$LayoutManager.onMeasure(android.support.v7.widget.RecyclerView$Recycler, android.support.v7.widget.RecyclerView$State, int, int)' on a null object reference
at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:1764)
at android.view.View.measure(View.java:17547)
2) 查看日志输出，似乎我的 Fragment 没有与 Activity 一起被销毁（如果我没记错的话，屏幕的旋转会破坏 activity 并开始一个新的）。
我想找到第 1 点的解决方案，但如果你能给我建议第 2 点的东西就更好了。
谢谢。 （请询问您是否需要更多代码，例如xml个文件）
将 onActivityCreated() 中的代码移至 onViewCreated() 中。在轮换时，您的 RecyclerView 可能会在 onActivityCreated() 回调被调用（您设置 LayoutManager 的位置）之前布局。
// I know that the recyclerView has been instantiated ( look at onCreateView() )
mRecyclerView = (RecyclerView) getActivity().findViewById(R.id.my_recycler_view);
您肯定不在 Fragment 中使用它。要在 Fragment 中获取视图，请将其放在 onCreateView 或 onViewCreated 中。你有你的片段的根视图实例，然后使用 View childView = rootView.findViewById(someId) 代替。
我很惊讶你只在方向改变时得到这个错误。您的 RecyclerView 需要正确设置 LayoutManager 才能正常工作。问题是您在 Activity 中创建了 RecyclerView，但在 Fragment 中对其进行了初始化，并且片段通常是异步添加或初始化的，这意味着在某些情况下 Activity 将尝试在执行位于 Fragment 中的初始化代码之前显示 RecyclerView。
RecyclerView 及其初始化代码应位于同一容器中：Activity 或 Fragment。避免从 Activity 访问 Fragment 视图或从 Fragment.
Activity 视图