java - RatingBar 错误 - 尝试在空对象引用上调用虚拟方法
问题描述
每次我尝试从我的 ratingbar 中获取评分时，我都会收到此错误：java.lang.NullPointerException: Attempt to invoke virtual method 'float android.widget.RatingBar.getRating()' on an null object reference
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.design.widget.TextInputLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.inputmethod.InputMethodManager;
import android.widget.RatingBar;
public class AddEditFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor> {
// defines callback method implemented by MainActivity
public interface AddEditFragmentListener {
// called when contact is saved
void onAddEditCompleted(Uri contactUri);
}
// constant used to identify the Loader
private static final int CONTACT_LOADER = 0;
private AddEditFragmentListener listener; // MainActivity
private Uri contactUri; // Uri of selected contact
private boolean addingNewContact = true; // adding (true) or editing
// EditTexts for contact information
private TextInputLayout titleTextInputLayout;
private TextInputLayout yearTextInputLayout;
private TextInputLayout directorTextInputLayout;
private TextInputLayout writerTextInputLayout;
private TextInputLayout producerTextInputLayout;
private TextInputLayout actorsTextInputLayout;
private RatingBar movieRatingBar;
private FloatingActionButton saveContactFAB;
private CoordinatorLayout coordinatorLayout; // used with SnackBars
// set AddEditFragmentListener when Fragment attached
@Override
public void onAttach(Context context) {
super.onAttach(context);
listener = (AddEditFragmentListener) context;
}
// remove AddEditFragmentListener when Fragment detached
@Override
public void onDetach() {
super.onDetach();
listener = null;
}
// called when Fragment's view needs to be created
@Override
public View onCreateView(
LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
setHasOptionsMenu(true); // fragment has menu items to display
// inflate GUI and get references to EditTexts
View view = inflater.inflate(R.layout.fragment_add_edit, container, false);
titleTextInputLayout = (TextInputLayout) view.findViewById(R.id.titleTextInputLayout);
titleTextInputLayout.getEditText().addTextChangedListener(nameChangedListener);
yearTextInputLayout = (TextInputLayout) view.findViewById(R.id.yearTextInputLayout);
directorTextInputLayout = (TextInputLayout) view.findViewById(R.id.directorTextInputLayout);
writerTextInputLayout = (TextInputLayout) view.findViewById(R.id.writerTextInputLayout);
producerTextInputLayout = (TextInputLayout) view.findViewById(R.id.producerTextInputLayout);
actorsTextInputLayout = (TextInputLayout) view.findViewById(R.id.actorsTextInputLayout);
movieRatingBar = (RatingBar) view.findViewById(R.id.ratingBar);
//zipTextInputLayout = (TextInputLayout) view.findViewById(R.id.zipTextInputLayout);
// set FloatingActionButton's event listener
saveContactFAB = (FloatingActionButton) view.findViewById(R.id.saveFloatingActionButton);
saveContactFAB.setOnClickListener(saveContactButtonClicked);
updateSaveButtonFAB();
// used to display SnackBars with brief messages
coordinatorLayout = (CoordinatorLayout) getActivity().findViewById(R.id.coordinatorLayout);
Bundle arguments = getArguments(); // null if creating new contact
if (arguments != null) {
addingNewContact = false;
contactUri = arguments.getParcelable(MainActivity.CONTACT_URI);
}
// if editing an existing contact, create Loader to get the contact
if (contactUri != null)
getLoaderManager().initLoader(CONTACT_LOADER, null, this);
return view;
}
// detects when the text in the titleTextInputLayout's EditText changes
// to hide or show saveButtonFAB
private final TextWatcher nameChangedListener = new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count,
int after) {}
// called when the text in titleTextInputLayout changes
@Override
public void onTextChanged(CharSequence s, int start, int before,
int count) {
updateSaveButtonFAB();
}
@Override
public void afterTextChanged(Editable s) { }
};
// shows saveButtonFAB only if the name is not empty
private void updateSaveButtonFAB() {
String input =
titleTextInputLayout.getEditText().getText().toString();
// if there is a name for the contact, show the FloatingActionButton
if (input.trim().length() != 0)
saveContactFAB.show();
else
saveContactFAB.hide();
}
// responds to event generated when user saves a contact
private final View.OnClickListener saveContactButtonClicked =
new View.OnClickListener() {
@Override
public void onClick(View v) {
// hide the virtual keyboard
((InputMethodManager) getActivity().getSystemService(
Context.INPUT_METHOD_SERVICE)).hideSoftInputFromWindow(
getView().getWindowToken(), 0);
saveContact(); // save contact to the database
}
};
// saves contact information to the database
private void saveContact() {
// create ContentValues object containing contact's key-value pairs
ContentValues contentValues = new ContentValues();
contentValues.put(Contact.COLUMN_TITLE, titleTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_YEAR, yearTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_DIRECTOR, directorTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_WRITER, writerTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_PRODUCER, producerTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_ACTOR, actorsTextInputLayout.getEditText().getText().toString());
//contentValues.put(Contact.COLUMN_RATING, zipTextInputLayout.getEditText().getText().toString());
contentValues.put(Contact.COLUMN_RATING, movieRatingBar.getRating());
if (addingNewContact) {
// use Activity's ContentResolver to invoke
// insert on the AddressBookContentProvider
Uri newContactUri = getActivity().getContentResolver().insert(Contact.CONTENT_URI, contentValues);
if (newContactUri != null) {
Snackbar.make(coordinatorLayout,
R.string.contact_added, Snackbar.LENGTH_LONG).show();
listener.onAddEditCompleted(newContactUri);
}
else {
Snackbar.make(coordinatorLayout,
R.string.contact_not_added, Snackbar.LENGTH_LONG).show();
}
}
else {
// use Activity's ContentResolver to invoke
// insert on the AddressBookContentProvider
int updatedRows = getActivity().getContentResolver().update(
contactUri, contentValues, null, null);
if (updatedRows > 0) {
listener.onAddEditCompleted(contactUri);
Snackbar.make(coordinatorLayout,
R.string.contact_updated, Snackbar.LENGTH_LONG).show();
}
else {
Snackbar.make(coordinatorLayout,
R.string.contact_not_updated, Snackbar.LENGTH_LONG).show();
}
}
}
// called by LoaderManager to create a Loader
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// create an appropriate CursorLoader based on the id argument;
// only one Loader in this fragment, so the switch is unnecessary
switch (id) {
case CONTACT_LOADER:
return new CursorLoader(getActivity(),
contactUri, // Uri of contact to display
null, // null projection returns all columns
null, // null selection returns all rows
null, // no selection arguments
null); // sort order
default:
return null;
}
}
// called by LoaderManager when loading completes
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
// if the contact exists in the database, display its data
if (data != null && data.moveToFirst()) {
// get the column index for each data item
int nameIndex = data.getColumnIndex(Contact.COLUMN_TITLE);
int phoneIndex = data.getColumnIndex(Contact.COLUMN_YEAR);
int emailIndex = data.getColumnIndex(Contact.COLUMN_DIRECTOR);
int streetIndex = data.getColumnIndex(Contact.COLUMN_WRITER);
int cityIndex = data.getColumnIndex(Contact.COLUMN_PRODUCER);
int stateIndex = data.getColumnIndex(Contact.COLUMN_ACTOR);
int rating = data.getColumnIndex(Contact.COLUMN_RATING);
// fill EditTexts with the retrieved data
titleTextInputLayout.getEditText().setText(data.getString(nameIndex));
yearTextInputLayout.getEditText().setText(data.getString(phoneIndex));
directorTextInputLayout.getEditText().setText(data.getString(emailIndex));
writerTextInputLayout.getEditText().setText(data.getString(streetIndex));
producerTextInputLayout.getEditText().setText(data.getString(cityIndex));
actorsTextInputLayout.getEditText().setText(data.getString(stateIndex));
//zipTextInputLayout.getEditText().setText(data.getString(zipIndex));
// movieRatingBar.setRating(data.getFloat(rating));
updateSaveButtonFAB();
}
}
// called by LoaderManager when the Loader is being reset
@Override
public void onLoaderReset(Loader<Cursor> loader) { }
}
错误出现在 contentValues.put(Contact.COLUMN_RATING, movieRatingBar.getRating());
我也试过简单地float rating = movieRatingBar.getRating(); 它给了我同样的错误。我有 movieRatingBar = (RatingBar) view.findViewById(R.id.ratingBar); 我听说很多有这个错误的人都错过了这条线。但它仍然不起作用
这是错误
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.enzo.addressbook, PID: 4134
java.lang.NullPointerException: Attempt to invoke virtual method 'float android.widget.RatingBar.getRating()' on a null object reference
at com.enzo.movieCollection.AddEditFragment.saveContact(AddEditFragment.java:165)
at com.enzo.movieCollection.AddEditFragment.access$100(AddEditFragment.java:26)
at com.enzo.movieCollection.AddEditFragment$2.onClick(AddEditFragment.java:148)
at android.view.View.performClick(View.java:6294)
at android.view.View$PerformClick.run(View.java:24770)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
I/zygote: After code cache collection, code=122KB, data=86KB
Increasing code cache capacity to 512KB
Application terminated.
解决方案
该错误意味着在这一行中：
movieRatingBar = (RatingBar) view.findViewById(R.id.ratingBar);
RatingBar找不到视图，所以结果movieRatingBar是null。
也许在 xml 中视图的 id 不是ratingBar，你拼错了吗？
或者它不间接属于那个布局？