我正在尝试实施Sliding Menu。当用户点击按钮时，我想显示两个片段，一个用于单击照片，另一个用于选择日期和时间。我正在使用DatePickerFragment来选择日期。我收到了NullPointerException
MainActivity()
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
// on first time display view for first nav item
displayView(0);
}
}
private void displayView(int position) {
// update the main content by replacing fragments
//HomeFragment homeFragment = null;
//ImageFragment imageFragment=null;
Fragment fragment=null;
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
DateTimeFragment datetime=null;
switch (position) {
case 0:
fragment= new HomeFragment();
break;
case 1:
fragment=new ImageFragment();
datetime=new DateTimeFragment();
break;
default:
break;
}
if(fragment!=null)
{
ft.replace(R.id.frame_container, fragment);
if(datetime!=null)
{
ft.replace(R.id.datetime_container, datetime);
}
ft.commit();
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
DateTimeFragment
import java.util.Calendar;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AutoCompleteTextView;
import android.widget.EditText;
import android.widget.ImageButton;
public class DateTimeFragment extends Fragment {
private EditText editStartDate;
private EditText editEndDate;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View v = inflater.inflate(R.layout.fragment_image, container, false);
final Calendar calendar = Calendar.getInstance();
int yy = calendar.get(Calendar.YEAR);
int mm = calendar.get(Calendar.MONTH)+1;
int dd = calendar.get(Calendar.DAY_OF_MONTH);
ImageButton startDate=(ImageButton)v.findViewById(R.id.start_date_button);
editStartDate = (EditText)v.findViewById(R.id.startDate);
editStartDate.setText(Integer.toString(dd)+ "/" + Integer.toString(mm) +"/"+ Integer.toString(yy));
ImageButton endDate=(ImageButton)v.findViewById(R.id.end_date_button);
editEndDate = (EditText)v.findViewById(R.id.endDate);
editEndDate.setText(Integer.toString(dd)+ "/" + Integer.toString(mm) +"/"+ Integer.toString(yy));
AutoCompleteTextView location= (AutoCompleteTextView)v.findViewById(R.id.location);
location.setAdapter(new PlacesAutoCompleteAdapter(getActivity(),R.layout.list_layout));
startDate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
try
{
DialogFragment newFragment= (DialogFragment) new DatePickerFragment(R.id.startDate);
newFragment.show(getActivity().getSupportFragmentManager(), "datePicker");
}
catch(Exception e)
{
return ;
}
}
});
endDate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try
{
DialogFragment newFragment= (DialogFragment) new DatePickerFragment(R.id.endDate);
newFragment.show(getActivity().getSupportFragmentManager(), "datePicker");
}
catch(Exception e)
{
return ;
}
}
});
return v;
}
public void onComplete(String date, int id) {
if(id==R.id.start_date_button)
editStartDate.setText(date);
else if(id==R.id.end_date_button)
editEndDate.setText(date);
}
}
imageFragment本身显示正确，但当我尝试显示DateFragment时，出现错误，如下所示：
12-26 16:17:39.023: E/AndroidRuntime(1799): FATAL EXCEPTION: main
12-26 16:17:39.023: E/AndroidRuntime(1799): Process: com.example.makemyday, PID: 1799
12-26 16:17:39.023: E/AndroidRuntime(1799): java.lang.NullPointerException
12-26 16:17:39.023: E/AndroidRuntime(1799): at com.example.makemyday.DateTimeFragment.onCreateView(DateTimeFragment.java:31)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.os.Handler.handleCallback(Handler.java:733)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.os.Handler.dispatchMessage(Handler.java:95)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.os.Looper.loop(Looper.java:136)
12-26 16:17:39.023: E/AndroidRuntime(1799): at android.app.ActivityThread.main(ActivityThread.java:5017)
12-26 16:17:39.023: E/AndroidRuntime(1799): at java.lang.reflect.Method.invokeNative(Native Method)
12-26 16:17:39.023: E/AndroidRuntime(1799): at java.lang.reflect.Method.invoke(Method.java:515)
12-26 16:17:39.023: E/AndroidRuntime(1799): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-26 16:17:39.023: E/AndroidRuntime(1799): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-26 16:17:39.023: E/AndroidRuntime(1799): at dalvik.system.NativeStart.main(Native Method)
有谁知道我做错了什么？
答案 0 :(得分：0)
正如您所看到的，您在第31行的DateTimeFragment类中的代码抛出了Null Pointer Exception。可能有些像ImageButtons这样的布局元素不是布局的一部分（或使用不同的Id），因此您的{{1 }}返回findViewById()