ArrayIndexOutOfBoundsException / passing arraylist from alertdialog to activity

问题

I have an alertdialog with multiple choices, I store the user's choices on an ArrayList of strings, and I want to pass the stored arraylist to the host activity (I will use the array's elements to query my database)..

When i run my app, i get an ArrayIndexOutOfBoundsException (may be the index is -1..), I'm not sure if it's the loop, or if i did not pass the arraylist correctly from the alertdialog...

can you guys take a look ? here is my function :

    public void onOkay(ArrayList<String> selected) {
    StringBuilder stringBuilder = new StringBuilder();
    if (selected.size() != 0) {
        for (int i = 0; i < selected.size(); i++) {
            String categories = selected_items_array[selected.indexOf(i)];
            stringBuilder = stringBuilder.append(" " + categories);
        }
        Toast.makeText(this, "You have selected: "
                + stringBuilder.toString(), Toast.LENGTH_SHORT).show();
    }

}

logcat :

java.lang.ArrayIndexOutOfBoundsException: length=6; index=-1
        at com.hichamridouane.smartshop.MainActivity.onOkay(MainActivity.java:164)
        at com.hichamridouane.smartshop.TimelineSettings$2.onClick(TimelineSettings.java:71)

here is my dialogfragment class. and here is my host activity.(as I said, i'm not sure if i'm passing correctly the arraylist to the host activity) thanks !

回答1:

It looks really strange to me, especially in

String categories = selected_items_array[selected.indexOf(i)];

From JavaDocs about indexOf

Returns the index of the first occurrence of the specified element
in this list, or -1 if this list does not contain the element.
More formally, returns the lowest index <tt>i</tt> such that
<tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,
or -1 if there is no such index.

So, you try to find element in your selected_items_array (not correct name in Java) in first iteration i == 0, selected_items_array have no such element => indexOf return -1. Array can't have element with index = -1, it starts from 0. So you have your ArrayIndexOutOfBoundsException

回答2:

Problem solved. Had to use Arraylists of integers in my activity and my dialogfragment.

here is what i did in my DialogFragment class:

public class TimelineSettings extends DialogFragment {
ArrayList<Integer> selected_categories = new ArrayList<Integer>();
boolean[] itemsChecked = {false, false, false, false, false, false};


// this interface to communicate with the host activity.

public interface dialoglistener {
    public void onOkay(ArrayList<Integer> selected);
    public void onCancel();
}
dialoglistener mlistener;


//this function is to instantiate the dialoglistener

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    try {
        mlistener = (dialoglistener) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " must implement dialogListener");
    }
}

My multichoice dialog :

    @Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    for(int i=0;i<itemsChecked.length;i++){
        if(selected_categories.contains((String)String.valueOf(i)))
            itemsChecked[i]=true;
    }

    // Set the dialog title
    builder.setTitle("Choisissez vos paramètres")
            .setMultiChoiceItems(R.array.categories, itemsChecked,
                    new DialogInterface.OnMultiChoiceClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int indexselected,
                                            boolean isChecked) {
                            if (isChecked) {
                                // If the user checked the item, add it to the selected items
                                if(!selected_categories.contains(indexselected)){
                                    selected_categories.add(indexselected);
                                    itemsChecked[indexselected]=true;
                                }
                            } else if (selected_categories.contains(indexselected)) {
                                // Else, if the item is already in the array, remove it
                                selected_categories.remove(indexselected);
                                itemsChecked[indexselected]=false;
                            }
                        }
                    })
                    // Set the action buttons
            .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int id) {
                    mlistener.onOkay(selected_categories);
                }
            })
            .setNegativeButton("Annuler", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int id) {
                    mlistener.onCancel();
                }
            });
    return builder.create();
}

On my host activity, I implemented the fragment's interface :

    @Override
public void onCreate(Bundle savedInstanceState) {
    /* some fancy stuff */
    Resources res = getResources();
    selectedArray = res.getStringArray(R.array.categories);
}

Getting the selected items (and show them on a toast, just for testing) :

    @Override
public void onOkay(ArrayList<Integer> selected) {
    StringBuilder stringBuilder = new StringBuilder();
    if (selected.size() != 0) {
        for (int i = 0; i < selected.size(); i++) {
            String categories = selectedArray[selected.get(i)];
            stringBuilder = stringBuilder.append(" " + categories);
        }
        Toast.makeText(this, "You have selected: "
                + stringBuilder.toString(), Toast.LENGTH_SHORT).show();
    }
}

来源：https://stackoverflow.com/questions/26992215/arrayindexoutofboundsexception-passing-arraylist-from-alertdialog-to-activity