列表内的按钮侦听器产生意外结果

Question

public class CustomerProductAdapter extends BaseAdapter {
Context ccon;
ImageView cprdctimg;

LayoutInflater cprdctinflater;
View cprdctview;
TextView cprdctname,cprdctdesc,cprdctprice,cprdctquant,cpquantity;
ArrayList<Product> cproduct;
Product currentproduct;
Button cpincq,cpdecq;
@Override
public int getCount() {
    return cproduct.size();
}

@Override
public Object getItem(int i) {
    return cproduct.get(i).getPname();
}

public CustomerProductAdapter(Context con,ArrayList<Product> product) {
    this.cproduct=product;
    this.ccon = con;
    cprdctinflater=LayoutInflater.from(con);
}

@Override
public long getItemId(int i) {
    return i;
}

@Override
public View getView(int i, View view, final ViewGroup viewGroup) {
    cprdctview=cprdctinflater.inflate(R.layout.cplist,null);
    cpincq=cprdctview.findViewById(R.id.cpincq);
    cpquantity=cprdctview.findViewById(R.id.cpquantity);
    cpdecq=cprdctview.findViewById(R.id.cpdecq);
    cprdctname=cprdctview.findViewById(R.id.cpname);
    cprdctdesc=cprdctview.findViewById(R.id.cpdesc);
    cprdctimg=cprdctview.findViewById(R.id.cppic);
    cprdctprice=cprdctview.findViewById(R.id.cpprice);
    cprdctquant=cprdctview.findViewById(R.id.cpquant);

    currentproduct=cproduct.get(i);
    cprdctimg.setImageResource(cproduct.get(i).getPimage());
    cprdctname.append(cproduct.get(i).getPname().toString());
    cprdctdesc.append(cproduct.get(i).getPdesc().toString());
    cprdctprice.append(cproduct.get(i).getPprice().toString());
    cprdctquant.append(cproduct.get(i).getPquant());

    cpincq.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            currentproduct.inccustomerquantity();
            if(currentproduct.getcustomerquantity()>Integer.parseInt(currentproduct.getPquant()))
            {
                Toast.makeText(viewGroup.getContext(), "You cannot order more than stock", Toast.LENGTH_SHORT).show();
                currentproduct.deccustomerquantity();
            }
            else {
                cpquantity.setText("" + currentproduct.getcustomerquantity());
            }
        }
    });
    cpdecq.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if(currentproduct.deccustomerquantity()) {
                cpquantity.setText("" + currentproduct.getcustomerquantity());
            }
        }
    });

    return cprdctview;
}
}

Here, if I increase the quantity of one product in the list, the corresponding TextView isn't changing.Instead some other TextView in a different list item is changed. As you can see in the image,the quantity of grapes changes when I click "+" symbol in banana item. Please help me to fix this error so that the change is made only to the appropriate textview.

Answer 1

When you click a button, you need to change the model in the list, not the UI. After that, update the desired position of the adapter. I suggest you look at the ViewHolder template.

Answer 2

GetView() is called everytime when creates a row. Therefore your global/instance variables ( currentproduct, cprdctname, cprdctdesc... ), are always refer to the last created row (when scroll up, the bottom one; when scroll down, the top one). You may save item row position as Tag to the buttons and update the corresponding item in data list. Then call adapter to redraw all the rows by notifyDataSetChanged().

Try this:

@Override
public View getView(int i, View view, final ViewGroup viewGroup) {
cprdctview=cprdctinflater.inflate(R.layout.cplist,null);
cpincq=cprdctview.findViewById(R.id.cpincq);
cpquantity=cprdctview.findViewById(R.id.cpquantity);
cpdecq=cprdctview.findViewById(R.id.cpdecq);
cprdctname=cprdctview.findViewById(R.id.cpname);
cprdctdesc=cprdctview.findViewById(R.id.cpdesc);
cprdctimg=cprdctview.findViewById(R.id.cppic);
cprdctprice=cprdctview.findViewById(R.id.cpprice);
cprdctquant=cprdctview.findViewById(R.id.cpquant);

currentproduct=cproduct.get(i);
cprdctimg.setImageResource(cproduct.get(i).getPimage());
cprdctname.append(cproduct.get(i).getPname().toString());
cprdctdesc.append(cproduct.get(i).getPdesc().toString());
cprdctprice.append(cproduct.get(i).getPprice().toString());
cprdctquant.append(cproduct.get(i).getPquant());

cpincq.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        currentproduct = cproduct.get((int)view.getTag()); // Get item for the clicked position
        currentproduct.inccustomerquantity();
        if(currentproduct.getcustomerquantity()>Integer.parseInt(currentproduct.getPquant()))
        {
            Toast.makeText(viewGroup.getContext(), "You cannot order more than stock", Toast.LENGTH_SHORT).show();
            currentproduct.deccustomerquantity();
        }
        else {
            //cpquantity.setText("" + currentproduct.getcustomerquantity());
            notifyDataSetChanged();
        }
    }
});
cpdecq.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        currentproduct = cproduct.get((int)view.getTag()); // Get item for the clicked position
        if(currentproduct.deccustomerquantity()) {
            //cpquantity.setText("" + currentproduct.getcustomerquantity());
            notifyDataSetChanged();
        }
    }
});

// Save the current position as Tag to the buttons
cpincq.setTag(i);
cpdecq.setTag(i);

return cprdctview;
}

Hope that helps!

Answer 3

As per android official documentation , do not use position as it gets reused . Using getAdapterPosition() is recommended. So in your code instead of listOfItems.get(i) use listOfItems(getAdapterPosition())