Question

Hello I am having a problem with my listivew. Please check my code below:

public void onItemClick(AdapterView<?> parent, View v, int position, long id) {
    // TODO Auto-generated method stub
    String selected;

    //selected = parent.getItemAtPosition(position).toString();

    selected = parent.getItemAtPosition(lv.getFirstVisiblePosition() + position).toString();

    if( selected.equals("Apple") ){
        Intent apple = new Intent(Fruits.this, Apples.class);
        startActivity(apple);
    }
    else if( selected.equals("Apricot") ){
        Intent apricot = new Intent(Fruits.this, Apricots.class);
        startActivity(apricot);
    }
    else if( selected.equals("Avocado") ){
        Intent avocado = new Intent(Fruits.this, Avocado.class);
        startActivity(avocado);
    }
    else if( selected.equals("Banana") ){
        Intent banana = new Intent(Fruits.this, Banana.class);
        startActivity(banana);
    }
    else if( selected.equals("Blackberry") ){
        Intent blackberry = new Intent(Fruits.this, Blackberries.class);
        startActivity( blackberry );
    }
    else if( selected.equals("Blueberry") ){
        Intent blueberry = new Intent(Fruits.this, Blueberry.class);
        startActivity(blueberry);
    }
    else if( selected.equals("Cranberry") ){
        Intent cranberry = new Intent(Fruits.this, Cranberry.class);
        startActivity(cranberry);
    }
    else if( selected.equals("Figs") ){
        Intent fig = new Intent(Fruits.this, Figs.class);
        startActivity(fig);
    }
    else if( selected.equals("Grapefruit") ){
        Intent grapefruit = new Intent(Fruits.this, Grapefruit.class);
        startActivity(grapefruit);
    }
    else if( selected.equals("Kiwi") ){
        Intent kiwi = new Intent(Fruits.this, Kiwi.class);
        startActivity(kiwi);
    }
    else if( selected.equals("Lemon") ){
        Intent lemon = new Intent(Fruits.this, Lemons.class);
        startActivity(lemon);
    }
    else if( selected.equals("Melon") ){
        Intent melon = new Intent(Fruits.this, Melon.class);
        startActivity(melon);
    }
    else if( selected.equals("Orange") ){
        Intent orange = new Intent(Fruits.this, Orange.class);
        startActivity(orange);
    }
    else if( selected.equals("Papaya") ){
        Intent papaya = new Intent(Fruits.this, Papaya.class);
        startActivity(papaya);
    }
    else if( selected.equals("Peach") ){
        Intent peach = new Intent(Fruits.this, Peaches.class);
        startActivity(peach);
    }
    else if( selected.equals("Pear") ){
        Intent pear = new Intent(Fruits.this, Pears.class);
        startActivity(pear);
    }
    else if( selected.equals("Pineapple") ){
        Intent pineapple = new Intent(Fruits.this, Pineapple.class);
        startActivity(pineapple);
    }
    else if( selected.equals("Plum") ){
        Intent plum = new Intent(Fruits.this, Plum.class);
        startActivity(plum);
    }
    else if( selected.equals("Prune") ){
        Intent prune = new Intent(Fruits.this, Prunes.class);
        startActivity(prune);
    }
    else if( selected.equals("Raspberry") ){
        Intent raspberry = new Intent(Fruits.this, Raspberry.class);
        startActivity(raspberry);
    }   
    else if( selected.equals("Rhubarb") ){
        Intent rhubard = new Intent(Fruits.this, Rhubard.class);
        startActivity(rhubard);
    }
    else if( selected.equals("Strawberry") ){
        Intent strawberry = new Intent(Fruits.this, Strawberries.class);
        startActivity(strawberry);
    }

} // end of OnItemClick method


final String[] classes = new String[] { 
        "Apple", // #0
        "Apricot", // #1
        "Avocado", // #2
        "Banana", // #3
        "Blackberry", // #4
        "Blueberry", // #5
        "Cranberry", // #6
        "Figs", // #7
        "Grapefruit", // #8
        "Kiwi", // #9
        "Lemon", // #10
        "Melon", // #11
        "Orange", // #12
        "Papaya", // #13
        "Peach", // #14
        "Pear", // #15
        "Pineapple", // #16
        "Plum", // #17
        "Prune", // #18
        "Raspberry", // #19
        "Rhubarb", // #20
        "Strawberry"  // #21
        };

Whenever I ran the application, it throws nullpointerexception in this line:

selected = parent.getItemAtPosition(lv.getFirstVisiblePosition() + position).toString();

What’s wrong with my code? Any help is truly appreciated. thanks.

Answer 1

You’re right, the error code is in the line:

selected = parent.getItemAtPosition(lv.getFirstVisiblePosition()+position).toString();

Because of the function: getFirstVisiblePosition() + position, sometimes will bigger than size of parent, your code will become: null.toString(), and of course, NullPointerException. You can check the document about the function :getFirstVisiblePosition in the Link to AdapterView here

Edited: I think you should not use this line anymore, just use: selected = classes[position]. That will solve your problem!