Workaround - placing the following script after the ScriptManager: 
<script type="text/javascript">
    Telerik.Web.UI.RadGantt.prototype.postback = function (args) {
        var postbackFunction = this.get_postBackReference().replace("arguments",
                Sys.Serialization.JavaScriptSerializer.serialize(args).replace(/\\/g, "\\\\").replace(/'/g, "\\'"));

        eval(postbackFunction);
    }
</script>

The task's get_customFieldClientName() and set_customFieldClientName(newValue) methods always work with the last custom field in the CustomFields collection.

There are two workarounds until an official solution is available:
- instead of the function getter, use task._data.customFieldClientName . The setter cannot be worked around that easily. This can work for you if you only show data or do not need to edit custom fields
- OR, add the following function override at the end of the </form>  - a sample is attached below
        <script>
            Telerik.Web.UI.RadGantt.prototype.initializeCustomFields = function () {

                var _createCustomFieldGetterAndSetter = function (fieldName) {
                    var taskType = Telerik.Web.UI.GanttTask;
                    taskType.prototype["get_" + fieldName] = function () {
                        return this._data[fieldName];
                    };

                    taskType.prototype["set_" + fieldName] = function (value) {
                        var updateInfo = {};
                        updateInfo[fieldName] = value;
                        this._data[fieldName] = value;
                        this._update(updateInfo);
                    };
                }

                var customFields = this.get_customTaskFields();
                for (var i = 0, length = customFields.length; i < length; i++) {
                    _createCustomFieldGetterAndSetter(customFields[i].clientPropertyName);
                }
            }
        </script>

There is a need to add custom buttons to the button strip of RadGantt.

The buttons for "Day | Week | Month" view appears on the top right of the RadGantt. The "Export to Pdf" button appears on the top left corner. I would like to add new buttons next to the "Export to Pdf" button. 

I would suggest taking this as a feature request. There are many scenarios where we need to have custom buttons in the toolbar of the RadGantt. Let the priority be decided by public opinion.

Allow setting a client template for the task's tooltip. 

Workaround: https://www.telerik.com/support/code-library/custom-task-tooltip

Currently, the RadGantt allows only format strings as a value for the WeekHeaderDateFormat property. For example, allowing a template similar to Kendo Gantt:
https://docs.telerik.com/kendo-ui/api/javascript/ui/gantt/configuration/views.weekheadertemplate#viewsweekheadertemplate 
https://docs.telerik.com/kendo-ui/api/javascript/ui/gantt/configuration/columns.headertemplate 

Use case - show week number instead of the dates. 

Workaround to show week number: The suggestion is based on the https://demos.telerik.com/aspnet-ajax/gantt/examples/accessibility-and-internationalization/localization/defaultcs.aspx demo. 

What you should add to the Gantt markup declaration is the WeekView-WeekHeaderDateFormat="dd/MM/yyyy" and OnClientDataBound="OnClientDataBound" properties. 

// https://stackoverflow.com/questions/6117814/get-week-of-year-in-javascript-like-in-php
function getWeekNumber(d) {
    // Copy date so don't modify original
    d = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
    // Set to nearest Thursday: current date + 4 - current day number
    // Make Sunday's day number 7
    d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay() || 7));
    // Get first day of year
    var yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
    // Calculate full weeks to nearest Thursday
    var weekNo = Math.ceil((((d - yearStart) / 86400000) + 1) / 7);
    // Return array of year and week number
    // return [d.getUTCFullYear(), weekNo];
    return weekNo
}
function OnClientDataBound(sender, args) {
    if (sender.get_viewsData()[sender.get_selectedView()].type == "week") {
        $telerik.$('.rgtTimelineWrapper thead>tr:first .radHeader', sender.get_element()).each(function (index) {
            var $this = $(this)
            var datestring = $this.text().substring(0, 10);
            var date = new Date(datestring);
            var weekNumber = getWeekNumber(date)
            $this.text("Week " + weekNumber)
        })
    }
}

Hello, this is for the list of columns on the left side of the Gantt, called TreeListView. If it would be possible to add additional columns that we select or implement during data binding, for example: Duration, other dates, description, task type, and many others that the client will select dynamically, so they must not be a static list of columns. 

Thank you,
-Sam 

In the RadGantt, when using WebServices with the Gantt, there is no OnClientRequestEnd client side event.

We have a scenario where we're wanting to be able to track whether or not an insert/update event succeeded (and update a control elsewhere on our page if it did) or failed (and show an alert if it didn't). however there is currently no event handler for when WebService requests from the RadGantt have completed.

I would like to use the RadGantt control in combination with my own RadWindow that would pop up as an edit control when clicking on a row in the treeview control of that object. There currently appear to be no client side events on the treeview. 

I would like the treeview to have a third mode that is not exactly "ReadOnly=True" or "ReadOnly=False", but would allow the row to be highlighted on click. The row data would not be editable, and clicking anywhere in a row would raise a client side event that I could trap.

Thanks for considering.

I have two dates for a Task[Eg: Plan Dates & Actual Dates]. I want to show both plan and actual dates in same row, both with different colors. Below I have attached an image for reference.


To show both Planned and Actual dates(if any) for a particular single task on the same row with different colors for both.

I need a context menu when user right click on particular task. Is it possible?

I am migrating MS Project Documents into Line of Business application into web pages. Which means everything MS Project can do, my client expect the telerik controls to do!

What I require is 'Go to' Date, where by the radGantt display can scroll to that position (eg like jumping to a # location)
This will allow the implementation of 'Go to 'Today'
This will allow the implementation of 'Go to 'dd/mm/yy'  
Where the date in in the center of the page, with an optional line (you are here) indicator. See https://www.officetimeline.com/plus for ideas.

I am migrating Excel Documents into Line of Business application into web pages. Which means everything excel can do, my client expect the telerik controls to do!

In your RadGantt controls, the Left hand side of the control is perceived to be a RadGrid this it is expected to have the same affordances of radGrid.
Which means that I expect the 
<CommandItemSettings ShowAddNewRecordButton="false" />
to work.

Which means I can apply all my learning of radGrid to the left hand side of radGantt.

I am migrating Excel Documents into Line of Business application into web pages. 
Which means everything excel can do, my client expect the telerik controls to do!
On either a RadGrid or RadGantt  I would like to be able to rotate the headings just like in Excel. 
An example is a heading like 'Days' but the actual value in that column is no bigger than 99.  
Another example if that the heading has a question, and the cell a check box.

We are missing the following navigation options (like the ones the RadScheduler has): go to the previous, next period (day/week/month) or go to a specific date.
Also, the views should show only the specified period (so the week view should show the current week by default). Now, if we have a task that started last year, even the day view shows several months of data.

If the RadGantt custom column could be a type of "Rich Text", then we could insert any html including link buttons (e.g. edit task ),  Icons ( e.g. tick for task complete), or rich text in red, green or whatever. 
We would also need the data_bind event available to populate the custom field. :)