How to attach GestureDetector to a ListPreference?

问题:

The challenge of attaching a GestureDetector to a ListPreference is 2-fold:

1. Getting a handle to a ListPreference that's only defined in a preferences.xml (i.e. not instantiated in Java code).
2. ListPreference is neither a View nor Activity subclass.

Is it possible at all to attach a GestureDetector to a ListPreference?

If so, how would one go about this? Where would I write the code to instantiate GestureDetector and implement the listener?

回答1:

Unless I didn't quite catch the question correctly, the answer is probably simpler than you might think. The source code for ListPreferece teaches that it's little more than a wrapper around an AlertDialog that displays its various options in a ListView. Now, AlertDialog actually allows you to get a handle on the ListView it wraps, which is probably all you need.

In one of the comments you indicated that, at this stage, all you're interested in is detecting a long-press on any item in the list. So rather than answering that by attaching a GestureDetector, I'll simply use an OnItemLongClickListener.

public class ListPreferenceActivity extends PreferenceActivity implements OnPreferenceClickListener {

    private ListPreference mListPreference;

    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        addPreferencesFromResource(R.xml.list_prefs);

        mListPreference = (ListPreference) findPreference("pref_list");
        mListPreference.setOnPreferenceClickListener(this);
    }

    @Override
    public boolean onPreferenceClick(Preference preference) {
        AlertDialog dialog = (AlertDialog) mListPreference.getDialog();
        dialog.getListView().setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override public boolean onItemLongClick(AdapterView<?> parent, View v, int position, long id) {
                Toast.makeText(getApplicationContext(), "Long click on index " + position + ": " 
                        + parent.getItemAtPosition(position).toString(), Toast.LENGTH_SHORT).show();
                return false;
            }
        });
        return false;
    }

}

The result (which the toast in the long-click displaying):

With a reference to the ListView, you could also attach an OnTouchListener, GestureDetector etc. Up to you to go from here.

回答2:

As @TronicZomB suggested, this isn't directly possible.

You can work around this by creating your own ListPreference derived class, getting its view in the inherited onBindDialogView().

Remember however that the latter is tricky because onBindDialogView() is only called if onCreateDialogView() doesn't return null, and this can happen only if you create your own custom view for YourListPreference.

The recommended way to do this is to build a custom Preference.

Once you have done that, you have a reference to YourListPreference's view, which is mandatory for attaching GestureDetector because one of the steps requires setOnTouchListener() on the view.

回答3:

I have set a GestrueDetector to a ScrollView using setOnTouchListener previously and searched for a similar method for ListPreference, however since the ListPreference does not contain such a method, I do not believe this will be possible.