Call non-static method (located in main class) from different class

Question

Thank you all for your answers and time!

Hello,

I've been trying to call a non-static method, located in my main application Class, from the Preferences Class. Because the method I call is not static, I instantiate the main class and then try to call the specific method I want but it's force closing.

Preferences.class (from where I call the method):

Preference sorted = (Preference) findPreference("sortPref");
        sorted.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
            public boolean onPreferenceChange(Preference preference, Object newValue) {
                Object d = new Dmarks();
                ((Dmarks) d).queryBookmarks();

                return true;
            }
        });

the Dmarks.class method I call:

    public void queryBookmarks() {

        Toast.makeText(context, "blah blah", Toast.LENGTH_LONG).show(); 
//context is not null and the Toast is working if I  call it from Dmarks.class

        }

The Logcat:

E/AndroidRuntime(11718): FATAL EXCEPTION: main
E/AndroidRuntime(11718): java.lang.NullPointerException
E/AndroidRuntime(11718):        at android.content.ContextWrapper.getContentReso
lver(ContextWrapper.java:90)
E/AndroidRuntime(11718):        at android.app.Activity.managedQuery(Activity.ja
va:1520)
E/AndroidRuntime(11718):        at com.droidil.droidmarks.Dmarks.queryBookmarks(
Dmarks.java:101)
E/AndroidRuntime(11718):        at com.droidil.droidmarks.Preferences$2.onPrefer
enceChange(Preferences.java:47)
E/AndroidRuntime(11718):        at android.preference.Preference.callChangeListe
ner(Preference.java:756)
E/AndroidRuntime(11718):        at android.preference.ListPreference.onDialogClo
sed(ListPreference.java:219)
E/AndroidRuntime(11718):        at android.preference.DialogPreference.onDismiss
(DialogPreference.java:384)
E/AndroidRuntime(11718):        at android.app.Dialog$ListenersHandler.handleMes
sage(Dialog.java:1047)
E/AndroidRuntime(11718):        at android.os.Handler.dispatchMessage(Handler.ja
va:99)
E/AndroidRuntime(11718):        at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime(11718):        at android.app.ActivityThread.main(ActivityThrea
d.java:4627)
E/AndroidRuntime(11718):        at java.lang.reflect.Method.invokeNative(Native
Method)
E/AndroidRuntime(11718):        at java.lang.reflect.Method.invoke(Method.java:5
21)
E/AndroidRuntime(11718):        at com.android.internal.os.ZygoteInit$MethodAndA
rgsCaller.run(ZygoteInit.java:868)
E/AndroidRuntime(11718):        at com.android.internal.os.ZygoteInit.main(Zygot
eInit.java:626)
E/AndroidRuntime(11718):        at dalvik.system.NativeStart.main(Native Method)

D/dalvikvm(11718): GC_FOR_MALLOC freed 4248 objects / 282248 bytes in 40ms
W/ActivityManager(  244):   Force finishing activity com.droidil.droidmarks/.Pre
ferences

Appreciate any help! :)

EDIT: I can't make queryBookmarks() a static function because it uses Android function managedQuery which is not a static function.

Answer 1

Where does context come from? It sounds like the exception is that context is null. Do you need to inject the context into your Dmarks instance yourself? Somehow, this value needs to be set.

Also, what is the point of code like this

Object d = new Dmarks();
((Dmarks) d).queryBookmarks();

instead of just writing

Dmarks d = new Dmarks();
d.queryBookmarks();

?

Answer 2

Contex maybe not null but looks like it's missing something, why don't you try to inject the actual instance of main class into Prefernces?

//in main    
preferncesInstance.setDmarks(this);

Then you can call queryBook on working instance...

Answer 3

Make Dmarks implement Preference.OnPreferenceChangeListener instead. Then you'll have a properly initialized context.

Answer 4

Dmarks is your primary Application class? You should not try to instantiate this in your Activity. Instead, use the getApplication function in your Activity to get the current instance.

You will need to cast it to your subclass type:

DMark dmark = (DMark)getApplication();
dmark.queryBookmarks();

Answer 5

i Think you must also call toast setView() and send suitable view