Tricky performance problem about UIButton's in UITableViewCell (iPhone)

I'm going to implement a view similar to the original photo app in iOS.

I created a customized UITableViewCell which has 4 UIButton in it. And it updates the button's image when the image array of the cell changed.

I worked hard to get the performance really satisfying. However, I found a tricky lag problem about it.

When I use my app normally, the scrolling is very smooth without significant lag. But if I keep the app (simulator) running on the "thumbnail grid view", and switch to other applications in Mac OS. After a while (maybe about 1 minute), when I switch back to the simulator, the scroll view gets stuck. It's hard to scroll it. If I click on something switching to another view and then switch back, everything is smooth again. So tricky.

I also tried the TTRemoteExamples which uses three20 to implement the grid view. It also gets stuck after switching between different applications in Mac OS (not in the iOS).

Then I tried not filling the customized cell with UIButton but 4 images. It didn't get stuck. So maybe the reason lies in the conflict between UITableViewCell and UIButton?

I don't know if it only happens on simulator or have potential performance problem when shipped to device (I haven't got the device to test on).

Apple's photo app will never be like this.

So I'm going to implement it from UIScrollView by myself to see if the problem is caused by the UITableView's mechanism. I still want to know the reason for the lag if anyone has come to it and solved it.

So开发者_运维知识库rry for my poor English, I hope you can catch my meaning.

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Who cares what the simulator does, seriously. Let it fart magical evil fairies that hijack the world's financial system causing it to enter a world of collapse...oh wait, maybe it already did that.

Seriously though, look at using code like AQGridView. It's very stable, provides an interface very much like a tableview, and is used in many projects. You also avoid the nonsense that is Three20 going this route. It's win-win.

But remember, always, and I do mean always, care what your app does on a device, if it isn't doing the same thing on the simulator, don't worry about it, you shouldn't be testing on the sim 99% of the time anyway. Users interact with your app on their devices, not your simulator. :)

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Referring to Subclassing UITableViewCell section in Table View Programming Guide for iOS, I finally solved the problem by implementing my custom mimicking the way from the guide, without adding subviews to UITableViewCell.

Apparently, adding too many subviews, only 4 in my code although, caused the strange problem I mentioned above. So, NEVER ADD SUBVIEWS, especially those with UIImageView's in it, to the contentView of UITableViewCell or UITableViewCell itself.

Instead, keep data's in the customized UITableViewCell, and do every drawing related thing in drawRect, using -[UIImage drawAtPoint:] and -[NSString drawAtPoint:withFont:].

In fact, the Apple's guide has mentioned it. It's careless of me skimming the part.

However, I'm still curious about why, as I mentioned, it only occurs when you switch between applications in your Mac OS, not iOS. I don't know the reason indeed.