Reload ListView not Working React Native

Question

Re-phrasing my Question... (Tested with separate class)

I am trying to reload listview with random array on a button press. But it's not working! Trying to do refresh datasource this with following LOC:

_buttonPressed() {
        this.setState({
            dataSource: this.state.dataSource.cloneWithRows(this._randomArray()),
        });
    }

_randomArray() {

    var jsonRes;

    switch(this.getRandomInt()) // number returned is valid. I checked
    {
        case 1:
        {
            jsonRes = '[' +
            '{ "firstName":"Michel" , "lastName":"John" ,"age":18},' +
            '{ "firstName":"Richard" , "lastName":"Joe","age":20 },' +
            '{ "firstName":"James" , "lastName":"Henry","age":15 },' +
            '{ "firstName":"e" , "lastName":"u","age":15 }]';
            break;
        }
        case 2:
        {
            jsonRes = '[' +
            '{ "firstName":"bacde" , "lastName":"John" ,"age":18},' +
            '{ "firstName":"bacde" , "lastName":"Joe","age":20 },' +
            '{ "firstName":"bacde" , "lastName":"Henry","age":15 },' +
            '{ "firstName":"ebacde" , "lastName":"u","age":15 }]';
            break;
        }
        case 3:
        {
            jsonRes = '[' +
            '{ "firstName":"mmmmm" , "lastName":"John" ,"age":18},' +
            '{ "firstName":"mmmmm" , "lastName":"Joe","age":20 },' +
            '{ "firstName":"mmmmm" , "lastName":"Henry","age":15 },' +
            '{ "firstName":"etttttt" , "lastName":"u","age":15 }]';
            break;
        }
        default:
        {
            jsonRes = '[' +
            '{ "firstName":"dddd" , "lastName":"John" ,"age":18},' +
            '{ "firstName":"dddd" , "lastName":"Joe","age":20 },' +
            '{ "firstName":"dddd" , "lastName":"Henry","age":15 },' +
            '{ "firstName":"ehhgh" , "lastName":"u","age":15 }]';
            break;
        }
    }

    var myObject = eval('(' + jsonRes + ')');
    return myObject;

}

I have already seen example listview projects of React Native. They are using dataSource.cloneWithRows for this purpose. Don't know what small thing I am missing. Please help me to sort out this issue... Thanks!

Answer 1

I have been able to successfully debug the issue. I just opened the source code for ListViewDataSource.js and traced the datablob variable value passed along the different functions.

A method _calculateDirtyArrays identifies which rows have been changed and need to be updated. For this, one of the three conditions must match for a row.

 ........
    // dirty if the section is new, row is new or _rowHasChanged is true
    dirty =
      !prevSectionsHash[sectionID] ||
      !prevRowsHash[sectionID][rowID] ||
      this._rowHasChanged(
        this._getRowData(prevDataBlob, sectionID, rowID),
        this._getRowData(this._dataBlob, sectionID, rowID)
      );
    this._dirtyRows[sIndex].push(!!dirty);
 ........

_rowHasChangedis the one passed to List Datasource constructor.

var dataSource = new ListView.DataSource(
{rowHasChanged: (r1, r2) => r1.guid !== r2.guid});

This was wrong in my case, since row should be changed when corresponding data changes. I changed above condition per my requirement.

var dataSource = new ListView.DataSource(
        {
            rowHasChanged: function(r1, r2) : bool {
                return (
                (r1["firstName"] !== r2["firstName"]) ||
                (r1["lastName"] !== r2["lastName"]) ||
                (r1["age"] !== r2["age"])
                );
            }
        });

and voila! It works perfect now. Hopefully it helps someone in future!