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POUIPinchGestureRecognizer how to use it correct?
 

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    <p>I have a simple chart control that display some lines. There are 3 properties involved in chart painting:</p> <ul> <li><code>RecordCount</code></li> <li><code>FirstVisibleIndex</code></li> <li><code>LastVisibleIndex</code></li> </ul> <p>Everything works ok, chart paints just fine between First &amp; Last Visible Record. Now I want to let user zoom in &amp; out the chart using 2 fingers, so I subscribed to <code>UIPinchGestureRecognizer</code> and implemented such a routine.</p> <pre><code>-(void)handleZoomGesture:(UIGestureRecognizer *)sender { if (_isChartBusy) { return; } UIPinchGestureRecognizer *gr = (UIPinchGestureRecognizer*)sender; if (gr.state != UIGestureRecognizerStateChanged &amp;&amp; gr.state != UIGestureRecognizerStateEnded) return; CGFloat scale = gr.scale; if (scale == 1) { return ; } if (_prevZoomScale == 0) { _prevZoomScale = scale; return; } int startIndex = chart.FirstVisibleIndex; int endIndex = chart.LastVisibleIndex; NSLog(@"Zoom. Scale: %f", scale); int stepZoom; int cnt = chart.LastVisibleIndex - chart.FirstVisibleIndex; stepZoom = cnt * 0.05; if (scale &lt; _prevZoomScale) { startIndex -= stepZoom; endIndex += stepZoom; } else { startIndex += stepZoom; endIndex -= stepZoom; } _prevZoomScale = scale; if (endIndex &lt; startIndex || (endIndex - startIndex) &lt; 10) { return; } if (startIndex &lt; 0) { startIndex = 0; } if (endIndex &gt;= [chart.DataProvider GetBarRecordCount]) { endIndex = [chart.DataProvider GetBarRecordCount] - 1; } if (startIndex == chart.FirstVisibleIndex &amp;&amp; endIndex == chart.LastVisibleIndex) { return; } chart.FirstVisibleIndex = startIndex; chart.LastVisibleIndex = endIndex; [self setNeedsDisplay]; } </code></pre> <p>it kinda works, but very unstable, chart gets "jumpy" when I try to move fingers and make the zoom operation. I cannot simulate a nice and smooth zoom in &amp; out experience. Are there any best approaches to achieve such a smooth change of VisibleIndexes in relation to how many Records I have in chart and how many are visible.</p>
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