在其中一个片段中，有一个RecyclerView带有自定义适配器，并且单击其中一个项目将转到另一个页面，该页面是相同Activity的新实例。但是，某些行为会在我的应用程序中导致错误。
从我的活动中，点击其中一个项目可以调出相同Activity的新实例，这很好。然后我按下后退按钮，然后回到第一个活动。但是，再次点击这些项目之一(启动同一活动的新实例)导致以下错误：
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
同样重要的是要考虑到我打电话了活动的新实例(即其中这三个项目是)，我在我的活动中的一个片段。所以，当我打电话吧，我有这样的：
public class MyActivity extends AppCompatActivity {
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
ViewPager viewPager = (ViewPager) findViewById(R.id.detail_viewpager);
viewPager.setAdapter(new ViewPagerAdapter(getSupportFragmentManager()));
TabLayout tabLayout = (TabLayout) findViewById(R.id.detail_tabs);
tabLayout.setTabTextColors(
ContextCompat.getColor(this, R.color.text_white_secondary),
ContextCompat.getColor(this, R.color.text_white));
tabLayout.setSelectedTabIndicatorColor(ContextCompat.getColor(this, R.color.white));
tabLayout.setupWithViewPager(viewPager);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
}
...
public class ViewPagerAdapter extends FragmentPagerAdapter {
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public int getCount() {
return 3;
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0: return new MainFragment();
case 1: return new MyFragment();
case 2: return new MyOtherFragment();
}
return null;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.tab_main_frag).toUpperCase(l);
case 1:
return getString(R.string.tab_my_frag).toUpperCase(l);
case 2:
return getString(R.string.tab_my_other_frag).toUpperCase(l);
}
return null;
}
}
...
public static class MyFragment extends Fragment implements MyRVAdapter.OnEntryClickListener {
...
private ArrayList mArrayList;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
...
doStuff();
...
}
private void doStuff() {
...
mArrayList = ...;
MyRVAdapter adapter = new MyRVAdapter(getActivity(), mArrayList);
adapter.setOnEntryClickListener(new MyRVAdapter.OnEntryClickListener() {
@Override
public void onEntryClick(View view, int position) {
Intent intent = new Intent(getActivity(), MyActivity.class);
intent.putExtra("INFORMATION", mArrayList.get(position));
startActivity(intent);
}
});
}
...
}
...
}
这里是我的自定义接口的一部分：
public class MyRVAdapter extends RecyclerView.Adapter {
public static class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
...
MyViewHolder(View itemView) {
super(itemView);
itemView.setOnClickListener(this);
...
}
@Override
public void onClick(View v) {
// The user may not set a click listener for list items, in which case our listener
// will be null, so we need to check for this
if (mOnEntryClickListener != null) {
mOnEntryClickListener.onEntryClick(v, getLayoutPosition());
}
}
}
private Context mContext;
private ArrayList mArray;
public MyRVAdapter(Context context, ArrayList array) {
mContext = context;
mArray = array;
}
@Override
public int getItemCount() {
return mArray.size();
}
@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.tile_simple, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(MyViewHolder holder, int position) {
ItemObj anItem = mArray.get(position);
...
}
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
super.onAttachedToRecyclerView(recyclerView);
}
private static OnEntryClickListener mOnEntryClickListener;
public interface OnEntryClickListener {
void onEntryClick(View view, int position);
}
public void setOnEntryClickListener(OnEntryClickListener onEntryClickListener) {
mOnEntryClickListener = onEntryClickListener;
}
}
这里是完全错误：
01-23 14:07:59.083 388-388/com.mycompany.myapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mycompany.myapp, PID: 388
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at ponentName.(ComponentName.java:77)
at android.content.Intent.(Intent.java:4570)
at com.mycompany.myapp.MyActivity$MyFragment$1.onEntryClick(MyActivity.java:783)
at com.mycompany.myapp.adapter.MyRVAdapter$MyViewHolder.onClick(MyRVAdapter.java:42)
at android.view.View.performClick(View.java:5197)
at android.view.View$PerformClick.run(View.java:20926)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:5951)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
错误指向第一行：Intent intent = new Intent(getActivity(), MyActivity.class);(来自片段)首先，线后(在错误中)指向mOnEntryClickListener.onEntryClick(v, getLayoutPosition());来自自定义适配器中的覆盖onClick方法河
我也读过类似的答案，但他们还没有解决我的问题。
编辑：
通过使用：
if (getActivity() == null) {
Log.d(LOG_TAG, "Activity context is null");
} else {
Intent intent = new Intent(getActivity(), MyActivity.class);
intent.putExtra("INFORMATION", mArrayList.get(position));
startActivity(intent);
} 在片段内部类(
onEntryClick)
，我发现主叫getActivity()返回null。
+2
'getActivity()'可能返回null。你在哪里设置你的'OnClickListener'？ –
+0
请添加java代码并且 - 没必要 - 问题出现在代码中 –
+0
它几乎听起来像您使用的是相同的Fragment，但带有一个新的Activity，因此当它获取Activity引用时，它不再存在。你是否在使用保留的片段，或者你是否将片段引用传递给活动的新实例？我们可能需要查看一些代码才能了解这一点。 –
android 字符串调用方法名 尝试在空对象引用上调用虚拟方法java.lang.String android.content.Context.getPackageName...
