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copied!<p><strong><em>UPDATE:</em></strong> See <a href="https://stackoverflow.com/questions/2188064/problems-invalidating-re-creating-nstimers/2188092#2188092">Darren's answer</a>. The problem is that you are not using your property accessor when setting the timers. Instead of:</p> <pre><code>incrementTimer = [NSTimer ... </code></pre> <p>You should have:</p> <pre><code>self.incrementTimer = [NSTimer ... </code></pre> <p>The <code>self.propertyName = ...</code> syntax will call your accessor method, and thereby automatically retain the object that you send to it (since your property is set up as <code>retain</code>). Simply calling <code>propertyName = ...</code> does <em>not</em> use the property accessor. You are simply changing the value of your ivar directly.</p> <hr> <p><strong><em>UPDATE #2:</em></strong> After an enlightening conversation with Peter Hosey (see comments), I have removed my earlier suggestion to "never retain or release" your timer object. I have also completely re-written my earlier code because I think the following is a better approach:</p> <blockquote> <p><strong>Controller.h</strong>:</p> </blockquote> <pre><code>NSTimer *voltageTimer; float targetBatteryVoltage; ... @property (nonatomic, retain) NSTimer *voltageTimer; </code></pre> <blockquote> <p><strong>Controller.m</strong>:</p> </blockquote> <pre><code>@implementation Controller @synthesize voltageTimer; - (void)stopVoltageTimer { [voltageTimer invalidate]; self.voltageTimer = nil; } - (void)setTargetBatteryVoltage:(float)target { [voltageTimer invalidate]; targetBatteryVoltage = target; self.voltageTimer = [NSTimer scheduledTimerWithTimeInterval: 2.0 target: self selector: @selector(updateBatteryVoltage:) userInfo: nil repeats: YES]; } - (void)updateBatteryVoltage:(NSTimer *)timer { const float increment = 0.1; if (abs(battVoltage - targetBatteryVoltage) < increment) { [timer invalidate]; } else if (battVoltage < targetBatteryVoltage) { generatorDisplay.battVoltage += increment; } else if (battVoltage > targetBatteryVoltage) { generatorDisplay.battVoltage -= increment; } } </code></pre> <p>Now, you can simply set a target battery voltage, and the timer magic will happen behind the scenes:</p> <pre><code>[self setTargetBatteryVoltage:24.0]; </code></pre> <p>Your power-off method would look as follows:</p> <pre><code>- (void)deEnergizeDisplays { [self stopVoltageTimer]; } </code></pre>

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