ContextMenu throws a NullPointerException

I'm trying to make a ContextMenu within my InputMethodService.

it gets initiates as

private ContextMenu ContextMenuInfo = null;

then within OnLongClick it has

ContextMenuInfo.setHeaderTitle("hello!");
ContextMenuInfo.add("aaa!");
ContextMenuInfo.add("bbb!");               开发者_JAVA百科 
mInputView.createContextMenu(ContextMenuInfo);

but it throws a NullPointerException. any ideas what might be missing?

Thanks!

edit:

tried with

public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo) {

menu.setHeaderTitle("Choose an option");
menu.add(0, v.getId(), 0, "Add to favorites");
menu.add(0, v.getId(), 0, "See details");

}

and within the longclick

registerForContextMenu( v );
openContextMenu( v );

but they both give

The method registerForContextMenu(View) is undefined for the type new View.OnLongClickListener(){}

So... you set ContextMenuInfo as null, then you try to call methods on it and you get a NullPointerException. That shouldn't be surprising. You're essentially calling null.setHeaderTitle("hello!");.

In onCreate(), have the lines:

Button b = (Button) findViewById(R.id.myButton);
registerForContextMenu(b);

Then, as you have, run these commands in onCreateContextMenu (or, more ideally, inflate the context menu from a resources xml file):

@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {

    menu.setHeaderTitle("Choose an option");
    menu.add(0, v.getId(), 0, "Add to favorites");
    menu.add(0, v.getId(), 0, "See details");
}

You can't call methods on a ContextMenuInfo object (or any object really) without instantiating it first.

Link for creating a context menu for a view.