Chart - chart not properly updated when binding of ActualMaximum and ActualMinimum is included.

Hello,

Please find attached a zipped demo project (just remove .txt).

I currently bind the ChartAxis properties Minimum, Maximum, ActualMaximum, ActualMinimum to viewmodel properties. They are all set to TwoWay binding.

Start the application.

1. Click the "Load Data ONE" button. (You should see one bar.) The call adds data and sets the values of the Minimum and Maximum through the binding. This view is not correct. Also note that the Reset Zoom button is enabled.

2. Next click the button "Update ActualMinMax" button. (You should see 10 bars.) This button click sets the values of ActualMaximum and ActualMinimum through the binding to be equal to the Maximum and Minimum values. This view is now correct. Also note that the ResetZoom button is disabled.

3. Next click the button "Load Data TWO". (You should see 4 bars) Though it show all the bars note that the X-Axis is the previous and that the "Reset Zoom" button is enabled.

4. Next click the button "Update ActualMinMax". The view should now show the 4 bars with proper x-axis scaling and the "Reset Zoom" button is disabled.

If there is "NO" binding set for the ActualMaximum and ActualMinimum then when we set the Minimum and Maximum axis values through the binding the data gets displayed properly scaled to the chart.

Question:

Shouldn't the chart also automatically scale itself when we bind the ActualMaximum and ActualMinimum as when we do not bind the ActualMaximum and ActualMinimum?

Or is it that whenever we bind Maximum, Minimum, ActualMaximum and ActualMinimum we have set all 4 values when first loading the data.

Thanks Oscar

p.s. The xaml has different chart binding scenarios which you can try and see the different behaviours. (see commented out parts.)

Hi Oscar,

Thanks for the repro project. Binding ActualMinimum and ActualMaximum gives you full control over those values. In the repro project that you sent, you are initially setting those values to zero, and so when you load the chart, the ActualMin and ActualMax values get set to zero as you have specified. To answer your question - When you bind all 4 values, you'll want to set all 4 values to be what you want.

I hope that explains it. Please let me know if you have further questions about this and I'll help you out.

-Jason Fauchelle

Thanks Jason.

I'm just curious if we only bind the Minimum and Maximum values but not the ActualMinimum and ActualMaximum and load the data set the Minimum and Maximum everything gets displayed properly.

How does the chartaxis know that the ActualMinimum and ActualMaximum are not bound or does the chartaxis by default sets the ActualMinimum and ActualMaximum to the Minimum and Maximum values when the Minimum and Maximum values change and afterward they get overwritten by the bound ActualMinimum and ActualMaximum?

Oscar

Hi Oscar,

Basically, whenever the ActualMinimum and ActualMaximum properties are set internally, the ChartAxis sets a flag to say that they are being set by some internal logic. When the ActualMin/Max properties are set outside the chart control - be it a binding, or directly setting the property - the internal flag is not set, and this is an indication that something outside the chart want's to take control of those values. So when those properties are set by you, another flag is set to disable the auto-viewport logic - that's the bit that sets ActualMin and ActualMax to be the min/max values when something changes. In fact, this flag is public - ChartAxis.IsAutoViewportEnabled - this property and the surrounding logic were added to solve other ActualMin/Max issues that you had in the past where the chart control was updating the viewport internally and overriding your bindings.

Hope that makes sense, let me know if you have further questions.

-Jason Fauchelle

Yes this makes sense. Thank you very much Jason for taking the time to explain. This helps give me a bigger picture and understand how it all connects.

Cheers Oscar