我正在制作一个应用程序，每当我等待很长时间才能使用该应用程序，因为它一直在后台运行，或者使用任务杀手（我实际上并没有使用任务杀手，它们只是方便地提出错误否则很难复制）然后当我按下我的应用程序上的按钮时，它崩溃了，我通过 logcat 发现这是因为 tempmainfrag 在以下代码中返回为 null 在 saveButtonClicked 和 deleteButtonClicked 方法中使用时：
public class MainActivity extends FragmentActivity
implements MainListFragment.OnListSelectedListener {
MainListFragment tempmainfrag;
InfoFragment infofrag;
int mainPosition = -1;
MenuItem menuItemAdd; //plus button in ActionBar/options menu
boolean menucreated = false;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mainlayout);
// Check whether the activity is using the layout version with
// the fragment_container FrameLayout. If so, we must add the first fragment
if (findViewById(R.id.fragment_container) != null) { //meaning, if using phone version
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create an instance of MainListFragment
tempmainfrag = new MainListFragment(); //made a context parameter to pass the context
// In case this activity was started with special instructions from an Intent,
// pass the Intent's extras to the fragment as arguments
tempmainfrag.setArguments(getIntent().getExtras());
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, tempmainfrag).commit();
Log.i("mydebug","TEMPMAINFRAG: " + tempmainfrag);
}
}
@Override
public void onResume()
{
super.onResume();
}
@Override
public void onStart()
{
Log.i("mydebug","1");
if(menuItemAdd != null)
menuItemAdd.setVisible(true); //turns on menu item 'add'
super.onStart();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu, menu);
menuItemAdd = menu.findItem(R.id.menu_add);
menucreated = true;
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_add: //NEED TO IMPLEMENT: MAKES ICON PRESS FOR BACK GO BACK
// Create fragment
infofrag = new InfoFragment(menuItemAdd);
Bundle args = new Bundle();
args.putBoolean(infofrag.ARG_NEW, true);
infofrag.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, infofrag);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void onItemSelected(int position, String schedulename, String[] ampm, boolean[] days, int[] times, boolean vibrate) {
// The user selected a list item
//////////////////////////////TWO PANE LAYOUT STUFF///////////////////////////////////
// Capture the article fragment from the activity layout
// InfoFragment articleFrag = (InfoFragment)
// getSupportFragmentManager().findFragmentById(R.id.article_fragment); //article_fragment exists in layout-large
//
// if (articleFrag != null) {
// // If article frag is available, we're in two-pane layout...
//
// // Call a method in the ArticleFragment to update its content
// articleFrag.updateArticleView(position);
//
// } else {
// phone layout - swap frags
mainPosition = position;
// Create fragment and give it an argument for the selected article
infofrag = new InfoFragment(menuItemAdd);
Bundle args = new Bundle();
args.putInt(infofrag.ARG_POSITION, position);
//new stuff to add info
args.putString(infofrag.ARG_NAME, schedulename);
args.putBooleanArray(infofrag.ARG_DAYS, days);
args.putIntArray(infofrag.ARG_TIMES, times);
args.putBoolean(infofrag.ARG_VIBRATE, vibrate);
args.putStringArray(infofrag.ARG_AMPM, ampm);
args.putBoolean(infofrag.ARG_NEW, false);
infofrag.setArguments(args);
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, infofrag);
transaction.addToBackStack(null);
// Commit the transaction
transaction.commit();
}
public void saveButtonClicked(View view) { //pass the click to the mainlistfragment
// MainListFragment tempmainfrag2 = (MainListFragment)getSupportFragmentManager().
// findFragmentById(R.id.fragment_container);
Log.i("mydebug","TEMPMAINFRAG: " + tempmainfrag);
if(!infofrag.newsched) //if existing schedule, so save
{
Log.i("mydebug","Saving schedule...");
boolean redo = false; //is set true every time info isnt correct when trying to save schedule
//create toast
Toast toast;
//get title
EditText titletext = (EditText)this.findViewById(R.id.titletext);
//get checkboxes
CheckBox check1 = (CheckBox)this.findViewById(R.id.monbox); //recreate checkboxes from view in activity (doesnt extend Activity
CheckBox check2 = (CheckBox)this.findViewById(R.id.tuebox); //so use getActivity())
CheckBox check3 = (CheckBox)this.findViewById(R.id.wedbox);
CheckBox check4 = (CheckBox)this.findViewById(R.id.thubox);
CheckBox check5 = (CheckBox)this.findViewById(R.id.fribox);
CheckBox check6 = (CheckBox)this.findViewById(R.id.satbox);
CheckBox check7 = (CheckBox)this.findViewById(R.id.sunbox);
CheckBox vibratebox = (CheckBox)this.findViewById(R.id.vibratecheckbox);
//get times
TimePicker startpicker = (TimePicker)this.findViewById(R.id.starttimepicker);
TimePicker stoppicker = (TimePicker)this.findViewById(R.id.stoptimepicker);
//check for input errors
if(titletext.getText().toString().length() == 0) //if title is empty
{
redo = true;
toast = Toast.makeText(view.getContext(), "Enter an event name", 4);
toast.show();
//some sick-ass shake animations!!!
Animation shake = AnimationUtils.loadAnimation(titletext.getContext(), R.anim.shake_big);
this.findViewById(R.id.titletext).startAnimation(shake);
}
else if((!check1.isChecked()) && (!check2.isChecked()) && (!check3.isChecked()) &&
(!check4.isChecked()) && (!check5.isChecked()) && (!check6.isChecked()) &&
(!check7.isChecked())) //if all checkboxes arent checked
{
redo = true;
toast = Toast.makeText(view.getContext(), "At least one day of week must be checked", 4);
toast.show();
//more sick-ass shake animations!!!
Animation shake = AnimationUtils.loadAnimation(titletext.getContext(), R.anim.shake_small);
this.findViewById(R.id.checkboxes).startAnimation(shake);
this.findViewById(R.id.daysofweek).startAnimation(shake);
this.findViewById(R.id.frequencytext).startAnimation(shake);
}
if(!redo) //if all info is fine
{
//check to see if time goes into next day
if((startpicker.getCurrentHour() > stoppicker.getCurrentHour())||
((startpicker.getCurrentHour() == stoppicker.getCurrentHour())
&& (startpicker.getCurrentMinute() >= stoppicker.getCurrentMinute())))
{
toast = Toast.makeText(view.getContext(), "Note: Stop time is earlier than start time, so this schedule stops at next day", Toast.LENGTH_LONG);
toast.show();
}
toast = Toast.makeText(view.getContext(), "Schedule saved", Toast.LENGTH_LONG);
toast.show();
//changing old schedule to new one
boolean[] tempdays = {check1.isChecked(), check2.isChecked(), check3.isChecked(), check4.isChecked(),
check5.isChecked(), check6.isChecked(), check7.isChecked()};
Log.i("mydebug","Time info read from counters: Start hour: " + startpicker.getCurrentHour() + "\nStop hour: " + stoppicker.getCurrentHour());
tempmainfrag.mainObjectList.changeSchedule(mainPosition, titletext.getText().toString(), tempdays, vibratebox.isChecked(),
startpicker.getCurrentHour(), startpicker.getCurrentMinute(), stoppicker.getCurrentHour(), stoppicker.getCurrentMinute());
//used to hide keyboard in case its still open when displaying list
InputMethodManager imm = (InputMethodManager)this.getSystemService(
Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(titletext.getWindowToken(), 0);
this.onBackPressed(); //replicates backpress to go back to list
}
}
else //if new schedule needs to be created
{
Log.i("mydebug","Creating new schedule...");
boolean redo = false;
//create toast
Toast toast;
//get title
EditText titletext = (EditText)this.findViewById(R.id.titletext);
//get checkboxes
CheckBox check1 = (CheckBox)this.findViewById(R.id.monbox); //recreate checkboxes from view in activity (doesnt extend Activity
CheckBox check2 = (CheckBox)this.findViewById(R.id.tuebox); //so use getActivity())
CheckBox check3 = (CheckBox)this.findViewById(R.id.wedbox);
CheckBox check4 = (CheckBox)this.findViewById(R.id.thubox);
CheckBox check5 = (CheckBox)this.findViewById(R.id.fribox);
CheckBox check6 = (CheckBox)this.findViewById(R.id.satbox);
CheckBox check7 = (CheckBox)this.findViewById(R.id.sunbox);
CheckBox vibratebox = (CheckBox)this.findViewById(R.id.vibratecheckbox);
//get times
TimePicker startpicker = (TimePicker)this.findViewById(R.id.starttimepicker);
TimePicker stoppicker = (TimePicker)this.findViewById(R.id.stoptimepicker);
EditText temppp = titletext;
//check for input errors
if(titletext.getText().toString().length() == 0) //if title is empty
{
redo = true;
toast = Toast.makeText(view.getContext(), "Enter an event name", 4);
toast.show();
//some sick-ass shake animations!!!
Animation shake = AnimationUtils.loadAnimation(titletext.getContext(), R.anim.shake_big);
this.findViewById(R.id.titletext).startAnimation(shake);
}
else if((!check1.isChecked()) && (!check2.isChecked()) && (!check3.isChecked()) &&
(!check4.isChecked()) && (!check5.isChecked()) && (!check6.isChecked()) &&
(!check7.isChecked())) //if all checkboxes arent checked
{
redo = true;
toast = Toast.makeText(view.getContext(), "At least one day of week must be checked", 4);
toast.show();
//more sick-ass shake animations!!!
Animation shake = AnimationUtils.loadAnimation(titletext.getContext(), R.anim.shake_small);
this.findViewById(R.id.checkboxes).startAnimation(shake);
this.findViewById(R.id.daysofweek).startAnimation(shake);
this.findViewById(R.id.frequencytext).startAnimation(shake);
}
if(!redo) //if all info is fine
{
//check to see if time goes into next day
if((startpicker.getCurrentHour() > stoppicker.getCurrentHour())||
((startpicker.getCurrentHour() == stoppicker.getCurrentHour())
&& (startpicker.getCurrentMinute() >= stoppicker.getCurrentMinute())))
{
toast = Toast.makeText(view.getContext(), "Note: Stop time is earlier than start time, so this schedule stops at next day", Toast.LENGTH_LONG);
toast.show();
}
toast = Toast.makeText(view.getContext(), "Schedule created", Toast.LENGTH_LONG);
toast.show();
//changing old schedule to new one
boolean[] tempdays = {check1.isChecked(), check2.isChecked(), check3.isChecked(), check4.isChecked(),
check5.isChecked(), check6.isChecked(), check7.isChecked()};
Log.i("mydebug","Time info read from counters: Start hour: " + startpicker.getCurrentHour() + "\nStop hour: " + stoppicker.getCurrentHour());
tempmainfrag.mainObjectList.addSchedule(titletext.getText().toString(), tempdays, vibratebox.isChecked(),
startpicker.getCurrentHour(), startpicker.getCurrentMinute(), stoppicker.getCurrentHour(), stoppicker.getCurrentMinute());
//used to hide keyboard in case its still open when displaying list
InputMethodManager imm = (InputMethodManager)this.getSystemService(
Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(titletext.getWindowToken(), 0);
this.onBackPressed(); //replicates backpress to go back to list
}
}
}
public void deleteButtonClicked(View view)
{
//tempmainfrag = (MainListFragment)getSupportFragmentManager().
//findFragmentById(R.id.fragment_container);
if(!infofrag.newsched) //if existing schedule, so ask to delete
{
//make a notification
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Delete?");
builder.setIcon(R.drawable.trash_icon);
builder.setMessage("Are you sure you wish to delete this schedule?")
.setCancelable(false)
.setPositiveButton("Delete", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
tempmainfrag.mainObjectList.removeSchedule(mainPosition);
Toast toast;
toast = Toast.makeText(tempmainfrag.getActivity(), "Schedule deleted", 4);
toast.show();
tempmainfrag.exit();
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.dismiss();
}
});
AlertDialog alert = builder.create();
alert.show();
}
else //if new schedule, so just cancel
tempmainfrag.exit();
}
public void hideKeyboard() //hides keyboard, called whenever reverting back to list
{
InputMethodManager imm = (InputMethodManager)getSystemService(
Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(this.getCurrentFocus().getWindowToken(), 0);
}
}
我意识到这是因为在 onCreate 中，saveinstancestate 不为空，所以没有创建新片段，那么有什么更好的方法来做到这一点呢？我尝试使用
MainListFrag tempmainfrag = (MainListFragment)getSupportFragmentManager().
findFragmentById(R.id.fragment_container);
但这也给了我错误。