title: Flutter Listview Builder in on click icon add and remove update quantity textfield
body: <p>I am trying to implement the cart functionality having add and remove quantity functions. I am using controller.text and updating to text field my issue is when i am adding and removing all the list items updated because of the same controller for text field how to separate update for each item?</p>
  
  <pre><code>ListView.builder(
      scrollDirection: Axis.vertical,
      itemCount: (data != null) ? (data["items"].length) * 20 : 0,
      itemBuilder: (BuildContext context, int index) {
  
        return Container(
          child: Column(
          children: &lt;widget&gt;[
          Container(
          alignment: Alignment.topLeft,
          width: double.infinity,
          child: Row(
            mainAxisAlignment: MainAxisAlignment.start,
            children: &lt;Widget&gt;[
              Container(
                  margin: const EdgeInsets.only(top: 8.0),
                  color: Colors.white,
                  child: ButtonTheme(
                    height: 16.0,
                    minWidth: 10.0,
                    child: RaisedButton(
                        padding: const EdgeInsets.all(4.0),
                        color: Colors.white,
                        child: Icon(Icons.remove,color: Colors.black,size: 20.0,),
                        onPressed: _removeQuantity
                    ),
                  )
              ),
  
              Container(
                  width: 60.0,
                  padding: const EdgeInsets.only(left: 1.0,right: 1.0),
                  child: Center(
                    child: TextField(
                      textAlign: TextAlign.center,
                      decoration: new InputDecoration(
                        hintText: "1",
                      ),
                      keyboardType: TextInputType.number,
                      controller: _quantityController,
                    ),
                  )
              ),
  
              Container(
                margin: const EdgeInsets.only(top: 8.0),
                color: Colors.white,
                child: ButtonTheme(
                  height: 16.0,
                  minWidth: 10.0,
                  child: RaisedButton(
                      padding: const EdgeInsets.all(4.0),
                      color: Colors.white,
                      child: Icon(Icons.add,color: Colors.black,size: 20.0),
                      onPressed: _addQuantity
                  ),
                ),
              ),
  
            ],
          ),
        ),
        ]
  </code></pre>
  
  <p><strong>Functions</strong></p>
  
  <pre><code>void _addQuantity(){
    setState(() {
      quantity++;
      _quantityController.text = '$quantity';
    });
  }
  
  void _removeQuantity(){
    setState(() {
  
      if(quantity &gt; 0){
        quantity--;
      }else{
        quantity = 0;
      }
      _quantityController.text = '$quantity';
    });
  }
  </code></pre>