Some customers have asked us why the end users are not able to update task start dates by dragging and dropping the left end of a task bar in an interactive Gantt Chart control, while the mouse cursor visually indicates a left-right drag possibility while hovering that bar area in the chart (assuming that the completion percent of the would be the default value of 0%).
The answer is simple:
- As designed: the start date of a task can be moved to the left or right by dragging the task bar while hovering its middle area; the task duration can be updated only by moving the right end of the task bar; and finally, task completion percent can be updated by moving the right end of the completion bar (usually displayed as a black rectangle inside the standard task bar).
- Moreover, as already indicated, the completion percent of a task item is 0% by default, and because of that, the completion bar of the task has a width of 0 pixels in this case, being virtually invisible and having its right end at the same position with its left end, and also with the left end of the main bar; therefore, when trying to move the left end of the task bar you are actually starting a drag operation for updating completion percent, moving the right end of the completion bar of the task.
To address this common confusion, in the latest build – 188.8.131.52 – of Gantt Chart Light Library, we have updated the default standard task bar templates for GanttChartView and GanttChartDataGrid controls (StandardTaskTemplate defaults) so that a small tool tip is now shown when hovering the right end of the completion bar of a task, displaying the current completion percent of the task, i.e. the value that is about to be changed.
You can provide similar visual hints the same way in your own templates if you are using components from other products or if you are using custom bar templates with Gantt Chart Light Library controls: define a ToolTip property on the Thumb element that provides drag and drop operation support for completion updates (i.e. having their role set to update completion property values) displaying a simple percent sign, another descriptive content, and/or the actual percent value from the data bound item, as needed.