title: in EXTJS 4 , how to add extra params when NEXT PAGE clicked on pagingtoolbar
body: <p>I use EXTJS 4.2.1.</p>
  
  <p>Here is my DATA STORE.</p>
  
  <pre><code>Ext.define("user",{
    extend:"Ext.data.Model",
    fields:[
      {name:'mobile',type:'string',sortable:true},
      {name:'name',type:'string',sortable:true},
      {name:'month',type:'string',sortable:true},
      {name:'city',type:'string',sortable:true},
      {name:'mail_number',type:'string',sortable:true}
    ]
  });
  
  var user = Ext.create("user",{});
  
  var ds = Ext.create("Ext.data.Store",{
      model:'user',
      storeId:'s_user',
      pageSize: 20,
      proxy:{
        type:'ajax',
        timeout: 40000,
        url:'JSONServlet',
        reader:{
          type:'json',
          root:'rows'
        },
        writer:{
          type:'json'
        }
      },
      autoLoad:false
   });
  </code></pre>
  
  <p>And i add some params where <code>ds</code> loads.</p>
  
  <pre><code>  ds.load({
                  params:{start:0, limit:20,     
                      'type': Ext.getCmp('type').value,  
                      'city': Ext.getCmp('city').value,  
                      'date': Ext.getCmp('date').value,
                      'date1': Ext.getCmp('date1').value
                  }       
              })
  </code></pre>
  
  <p>I put a <code>pagingtoolbar</code> on the bottom of  the grid.</p>
  
  <pre><code>  var grid = Ext.create("Ext.grid.Panel",{
  
        ...
  
        dockedItems :[{
            xtype:'pagingtoolbar',
            store:Ext.data.StoreManager.lookup('s_user'),
            dock:'bottom',
            displayInfo:true
        }],
  
        ...
        store : Ext.data.StoreManager.lookup('s_user')
    }
  </code></pre>
  
  <p>On the first page everything is OK, but when NEXT page is clicked, <code>ds</code> pramas don't  <code>POST</code> to server.
  I look into the source. I find code like this.</p>
  
  <pre><code>      case "next":  
                  ds.load({params:{start: this.cursor+this.pageSize, limit: this.pageSize}});  
              break;
  </code></pre>
  
  <p>how to make PAGE NEXT work as i want,  I hope someone give me  a hint.</p>