Question

I am working on a shopping cart assignment for that I have created a custom ListView that contains the Picture, Price and Add to Cart button in each row.
I also have a textview at the top which increments everytime the user presses the Add to cart.
The Button in every row is perfectly working fine but I don’t know how to increment the counter and set it to the textview as whenever I do this under onClick event I get runtime error.
I am sharing with you the code.

package uet.cs08.bll;

import java.util.ArrayList;

import uet.cs08.android.R;
import uet.cs08.android.mainActivity2;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;

public class itemBaseAdapter extends BaseAdapter  {

 public int count = 5;
 private ArrayList<ItemInfo> itemList;
 private LayoutInflater mInflater;

 public itemBaseAdapter(Context context, ArrayList<ItemInfo> itemList){
     this.itemList=itemList;
     mInflater= LayoutInflater.from(context);

 }
@Override
public int getCount() {
    return itemList.size();

}

@Override
public Object getItem(int idx) {
     return itemList.get(idx);
}

@Override
public long getItemId(int idx) {
    // TODO Auto-generated method stub
    return idx;
}

@Override
public View getView(int idx,  View convertView, ViewGroup parent) {
    final ViewHolder holder;
    if(convertView==null){

        convertView=mInflater.inflate(R.layout.item_list_row, null);
        holder = new ViewHolder();
        holder.txtItemName=(TextView)  convertView.findViewById(R.id.itemName);
        holder.txtPic=(ImageView) convertView.findViewById(R.id.pic);
        holder.txtPrice=(TextView) convertView.findViewById(R.id.price);
        holder.counter = (TextView) convertView.findViewById(R.id.tvCount);
        Button btn = (Button) convertView.findViewById(R.id.Cart);
        final TextView tv = (TextView)convertView.findViewById(R.id.tvCount);


        btn.setOnClickListener(new View.OnClickListener() {
        @Override
            public void onClick(View v) {

                 count = Integer.parseInt((String)tv.getText());
                 count++;
                 tv.setText("" + count);


        }
        });
            //tv.setText(""+count);         
            convertView.setTag(holder);
    }else
    {
           holder = (ViewHolder) convertView.getTag();
    }

    holder.txtItemName.setText(itemList.get(idx).itemName);
    holder.txtPic.setImageResource(itemList.get(idx).pic);
    holder.txtPrice.setText(""+itemList.get(idx).price);
    holder.counter.setText(itemList.get(idx).count);

    return convertView;
}


class ViewHolder {
      TextView txtItemName;
      ImageView txtPic;
      TextView txtPrice;
      TextView counter;
     }

}
`
Here is the logCat.

03-20 16:16:38.853: D/AndroidRuntime(2759): Shutting down VM
03-20 16:16:38.853: W/dalvikvm(2759): threadid=1: thread exiting with uncaught exception (group=0x40015560)
03-20 16:16:38.883: E/AndroidRuntime(2759): FATAL EXCEPTION: main
03-20 16:16:38.883: E/AndroidRuntime(2759): java.lang.NullPointerException
03-20 16:16:38.883: E/AndroidRuntime(2759):     at uet.cs08.bll.itemBaseAdapter$1.onClick(itemBaseAdapter.java:61)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.view.View.performClick(View.java:2485)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.view.View$PerformClick.run(View.java:9080)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.os.Handler.handleCallback(Handler.java:587)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.os.Handler.dispatchMessage(Handler.java:92)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.os.Looper.loop(Looper.java:123)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at java.lang.reflect.Method.invokeNative(Native Method)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at java.lang.reflect.Method.invoke(Method.java:507)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-20 16:16:38.883: E/AndroidRuntime(2759):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

Make sure you have reference to your TextView in xml.

Connect it (using findViewById()) inside onCreate() of Activity only, and you may pass it to your Adapter (i.e making a class field and setter getter method), if Adapter is a separate class.

and dont do this inside getView() of Adapter, remove this line.

final TextView tv  = (TextView)convertView.findViewById(R.id.tvCount);

you will pass your TextView from Activity to Adapter using constructor or setter getter method, will keep a reference using class Adapter's class level variable and the what you will do inside onClick() of Button is:

btn.setOnClickListener(new View.OnClickListener() {
     @Override
     public void onClick(View v) {
          count++;
         yourClassLevelTextView.setText(String.valueOf(count));
     }});

EDIT:

how you will pass TextView to Adapter

public class YourAdapter extends BlahBlahBlah
{
     private TextView yourClassLevelTextView;
     public void setTextView(TextView textViewFromActivity)
     {
         this.yourClassLevelTextView = textViewFromActivity;
     }
}

and in Activity do something like this:

YourAdapter adapter = new YourAdapter(blah, blah, blah);
adapter.setTextView(yourTextViewInActivity);
listView.setAdapter(adapter);