Swift中Timer失效后重新初始化无法正常工作的问题

I've run into this exact issue before—let's break down what's going wrong and how to fix it quickly.

The Root Cause #

When you call invalidate() on your itemPlayTimer, the timer gets removed from the RunLoop, but your itemPlayTimer variable still holds a reference to the invalidated timer instance. That means when you call startTimer() again, the check if itemPlayTimer != nil { return } skips creating a new timer entirely.

Step-by-Step Solutions #

1. Always Nil Out the Timer After Invalidation

First, update your pause logic to not just invalidate the timer, but set the variable to nil:

func pausePlayerAndTimer() {
    // Pause your audio player first
    player?.pause()
    
    // Invalidate and nil the timer
    itemPlayTimer?.invalidate()
    itemPlayTimer = nil // Critical line!
}

2. Refine the startTimer() Logic

To make your timer initialization more robust, add a cleanup step at the start of startTimer()—this ensures no stale timer references are left behind:

func startTimer() { 
    print("PlayerController: startTimer()") 
    
    // Clean up any existing timer first
    itemPlayTimer?.invalidate()
    itemPlayTimer = nil
    
    // Create the new timer
    itemPlayTimer = Timer.scheduledTimer(
        timeInterval: 0.001, 
        target: self, 
        selector: #selector(updateItemPlayerTimer), 
        userInfo: nil, 
        repeats: true
    )
    
    // Optional: Add to .common RunLoop mode to keep updating during UI interactions (like scrolling)
    RunLoop.current.add(itemPlayTimer!, forMode: .common)
}

3. Bonus: Avoid Circular References with Block-Based Timers

The selector-based timer can create a circular reference between self and the timer. Switch to a block-based timer with a weak reference to self to fix this:

func startTimer() { 
    print("PlayerController: startTimer()") 
    
    itemPlayTimer?.invalidate()
    itemPlayTimer = nil
    
    itemPlayTimer = Timer.scheduledTimer(withTimeInterval: 0.001, repeats: true) { [weak self] timer in
        guard let self = self, let currentTime = self.player?.currentTime else {
            // Invalidate the timer if we lose reference to self or the player
            timer.invalidate()
            return
        }
        self.updateTimeDescription?(currentTime)
    }
    
    RunLoop.current.add(itemPlayTimer!, forMode: .common)
}

Why This Works #

• Nil-ing out itemPlayTimer after invalidation ensures your startTimer() check doesn't skip creating a new timer.
• Adding the timer to .common RunLoop mode ensures it keeps firing even when the user is interacting with the UI (like scrolling a table view).
• Block-based timers with [weak self] prevent memory leaks that could cause unexpected behavior down the line.

内容的提问来源于stack exchange，提问作者Dmitry Kuleshov