why Viewholder in the listview can't handle two textviews?

Question

i get a fragment with listview inside another fragment,and the listview have a viewholder class like this:
private class ViewHolder{ TextView rowText1; TextView rowText2; }

and give the textview very simple task:

holder.rowText1.setText(someString); holder.rowText2.setText(someString);

The Log give me a nullpointer error:

java.lang.NullPointerException:
Attempt to invoke virtual method void android.widget.TextView.setText(java.lang.CharSequence) on a null object reference

But if i just give one view settext(any one), everything works fine:

holder.rowText1.setText(someString);
//holder.rowText2.setText(someString);

Any ideas why?

My viewholder code:

 public View getView(int position, View convertView, ViewGroup parent) {
        int type = getItemViewType(position);
        ViewHolder holder;
        if(convertView == null){
            holder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.some_layout, parent,false);                          
            switch(type){
                case 1:
                    holder.rowText1 = (TextView) convertView.findViewById(R.id.textView1);                                              
                   break;
                case 2:
                    holder.rowText1  = (TextView) convertView.findViewById(R.id.textView1);
                    holder.rowText2 =(TextView)convertView.findViewById(R.id.textView2);

                    ImageView fileImage = (ImageView)convertView.findViewById(R.id.typeImage);
                    fileImage.setImageDrawable(fileDrawable);
                    break;
            }
            convertView.setTag(holder);
        }else {
           holder = (ViewHolder) convertView.getTag();
        }

Also,i dug a little bit ,find the problem seems to be in the view recycle stage,somehow when the system began to recycle the view ,with two views,it just doesnt work.

What is the problem? Looks like you did not finish writing this question before posting it. — laalto, Oct 20 '17 at 11:07
sorry, this is my first post, i am trying to make the format right,now the question is finished. — coldspring, Oct 20 '17 at 11:11
So you've forgotten to init `rowText2` or it is init with null. Post the code where you set up the view holder. — laalto, Oct 20 '17 at 11:12
I dont think so,using either of the two is ok,just wrong using both.I post the view holder code — coldspring, Oct 20 '17 at 11:24
OK, after some looking,i find you are right ,it was due to the reason i put the settext code outside the switch clause,so when in case 1,rowtext2 still want to settext. thanks! — coldspring, Oct 21 '17 at 03:33

Ellisan · Answer 1 · 2017-10-20T11:51:40.993

What about changing your getView to this?

public View getView(int position, View convertView, ViewGroup parent) {
    if(convertView == null){
        convertView = LayoutInflater.from(getContext()).inflate(R.layout.some_layout, parent,false)
        int type = getItemViewType(position);
        ViewHolder holder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.some_layout, parent,false);                          
            switch(type){
                case 1:
                    holder.rowText1 = (TextView) convertView.findViewById(R.id.textView1);                                              
                   break;
                case 2:
                    holder.rowText1  = (TextView) convertView.findViewById(R.id.textView1);
                    holder.rowText2 =(TextView)convertView.findViewById(R.id.textView2);                       
                    ImageView fileImage = (ImageView)convertView.findViewById(R.id.typeImage);
                    fileImage.setImageDrawable(fileDrawable);
                    break;
        }
        convertView.setTag(holder);
    }
    return convertView;
}

This only does everything once and if the convertView isn't null it will return the already existing view.

For more info regarding adapters, view this: How does the getView() method work when creating your own custom adapter?

Can you explain the logic? Isn't the point we should avoid calling inflate everytime? — coldspring, Oct 20 '17 at 11:45
You aren't inflating it every time but only when convertView is null. Howeveryou can try putting what i have outside the if (except the return) inside of it. Check updated answer — Ellisan, Oct 20 '17 at 11:50
Thanks for your time, the problem is solved,i didn't initiate properly,i will post the solution as an answer — coldspring, Oct 21 '17 at 03:35

coldspring · Answer 2 · 2017-10-21T12:51:27.327

oK,so i solve the problem,as you can see in my original getview code,it didn'T include settext code.I put it after that,so adjust the code in this way(simply add the settext code):

switch(type){
                case 1:
              holder.rowText1 = (TextView)convertView.findViewById(R.id.textView1);
                holder.rowText1.setText(someString);                                                                                                             
                    break;
                case 2:
                    holder.rowText1  = (TextView) convertView.findViewById(R.id.textView1);
                    holder.rowText2 =(TextView)convertView.findViewById(R.id.textView2);                       
                    holder.rowText1.setText(someString);
                   holder.rowText2.setText(someString);
                  ImageView fileImage = (ImageView)convertView.findViewById(R.id.typeImage);
                fileImage.setImageDrawable(fileDrawable);
                    break;
            }

As you can see,because i only want to have one textview in case 1,when i put the settext code outside the switch clause,even in case 1,it still want to execute settext to rowtext2.it is a pretty dumb mistake,newbie spotted!!

why Viewholder in the listview can't handle two textviews?

2 Answers2