【发布时间】：2016-02-24 18:41:31
【问题描述】：
我正在尝试在我的社交网络 iOS 应用程序中实现一个点赞功能 - 使用 Swift、Parse 作为后端和 Storyboard - 用户可以在其中喜欢（和不喜欢）类似于 Instagram 或 Facebook iOS 应用程序的帖子。
唯一的问题似乎是，当用户滚动帖子的 tableview 提要时，当前用户不喜欢的其他帖子显示填充的喜欢按钮图像（好像他们被喜欢，但他们不是） .
根据我的研究，我了解到这可能是因为 tableview 中的单元格是可重复使用的（通过 tableView.dequeueReusableCellWithIdentifier.）* 这是有道理的，因为当用户打开应用程序时，只有可见的单元格被加载.并且当用户滚动 tableview 时，单元格会被回收。
因此，我进行了更多研究，发现尝试解决此问题的一种方法是使用prepareForReuse() 方法重置自定义单元格的likeButton IBOutlet 图像。 tableView:cellForRowAtIndexPath: 中的 table view 的委托然后在重用单元格时重置所有内容，包括 likeButton 图像以及基于从 like 查询获得的结果的一些逻辑。它最初可以工作，但不幸的是，当用户尝试点赞帖子时，由于某种原因，这会破坏点赞按钮的行为。
更新：这里不需要 prepareForResuse() 作为答案的建议之一。
// In custom cell file:
override func prepareForReuse() {
super.prepareForReuse()
// Set likeButton image to the default unfilled version
let image = UIImage(named: "likeButtonUnfilled")
self.likeButton.setImage(image, forState: UIControlState.Normal)
}
在 post feed viewcontroller 文件的cellForRowAtIndexPath 中：
// currUserLikeObjects is an array of PFObjects that contains the results returned from the like query (all of the objects that the current user has liked)
for object in currUserLikeObjects {
if object["toPost"]?.objectId! == postObject.objectId {
// Toggle likeButton image to filled version
let image = UIImage(named: "likeButtonFilled") as UIImage!
cell.likeButton.setImage(image, forState: UIControlState.Normal)
}
}
在likeButtonTappedpost feed viewcontroller 文件中：
func likeButtonTapped(sender: UIButton) {
sender.enabled = false
let indexPath = NSIndexPath(forRow: sender.tag, inSection: 0)
let cell = tableView.cellForRowAtIndexPath(indexPath) as! PostTableViewCell
let likeObject = PFObject(className: ParseHelper.ParseLikeClass)
var likedPost: PFObject = (self.objects![indexPath.row] as? PFObject)!
if (cell.likeButton.currentImage!.isEqual(UIImage(named: "likeButtonUnfilled"))) {
/* The post is NOT liked already by the currentUser (likeButton image is NOT filled)
1. Save the like object to Parse
2. If successfully saved, increment the likeCount and update it in Parse (Remember: Enable likeButton)
3. If successfully saved, toggle the image to the filled version
*/
// 1
likeObject["fromUser"] = PFUser.currentUser()!
likeObject["toPost"] = likedPost
likeObject.saveInBackgroundWithBlock { (success: Bool, error: NSError?) -> Void in
if (error == nil) {
print("SUCCESS: Saved likeObject in database.")
// 2
likedPost.incrementKey(ParseHelper.ParsePostLikeCount, byAmount: 1)
likedPost.saveInBackgroundWithBlock { (success: Bool, error: NSError?) -> Void in
if (error == nil) {
// The likeCount key has been incremented
print("SUCCESS: The likeCount key has been incremented. Toggling like button image to FILLED.")
// 3
var image = UIImage(named: Helper.likeButtonFilled)
cell.likeButton.setImage(image, forState: UIControlState.Normal)
} else {
// There was a problem, check error.description
print("FAIL: The likeCount key has NOT been incremented.")
// Delete the likeObject since the likeCount was not successfully saved
likeObject.deleteInBackgroundWithBlock( {(succeeded: Bool?, error: NSError?) -> Void in
if (error == nil) {
print("SUCCESS: Deleted likeObject from Parse since likeCount key has not successfully been incremented.")
self.showAlertMessage((error?.description)!)
} else {
print("FAIL: Unable to delete the likeObject from Parse in response to likeCount key NOT incrementing.")
}
})
}
}
print("Enabling sender & reloading data.")
sender.enabled = true
self.tableView.reloadData()
} else {
print("FAIL: Unable to save like object in Parse.")
self.showAlertMessage("Unable to like this post at this time.")
}
}
} else if (cell.likeButton.currentImage!.isEqual(UIImage(named: "likeButtonFilled"))) {
/* The post is liked already by the currentUser (likeButton image is filled)
1. Delete the likeObject from Parse
2. If successfully deleted, only if the likeCount is greater than 0 to avoid a negative likeCount, decrement the likeCount and update it in Parse (Remember: Enable likeButton)
3. If successfully deleted, toggle the image to the unfilled version
*/
// 1
likeObject.deleteInBackgroundWithBlock( {(succeeded: Bool?, error: NSError?) -> Void in
if (error == nil) {
print("SUCCESS: Deleted likeObject from Parse (unliked post).")
// 2
likedPost.incrementKey(ParseHelper.ParsePostLikeCount, byAmount: -1)
likedPost.saveInBackgroundWithBlock { (success: Bool, error: NSError?) -> Void in
if (error == nil) {
// The likeCount key has been decremented
print("SUCCESS: The likeCount key has been decremented.")
// 3
var image = UIImage(named: Helper.likeButtonUnfilled)
cell.likeButton.setImage(image, forState: UIControlState.Normal)
} else {
print("FAIL: The likeCount key has NOT been decremented.")
// Delete the likeObject from the Like class since the likeCount was not successfully saved?
}
}
print("Enabling sender & reloading data.")
sender.enabled = true
self.tableView.reloadData()
} else {
print("FAIL: Unable to delete the like object from Parse.")
}
})
}
}
【问题讨论】：