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 - 用户可以在其中点赞(和点赞)类似于 Instagram 或 Facebook iOS 应用程序的帖子。

唯一的问题似乎是，当用户滚动帖子的表格 View 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，但他们没有) .

根据我的研究，我了解到这可能是因为 tableview 中的单元格是可重用的(通过 tableView.dequeueReusableCellWithIdentifier。)* 这是有道理的，因为当用户打开应用程序时, 仅加载可见单元格。当用户滚动表格 View 时，单元格将被回收。

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() 方法来重置自定义单元格的 likeButton IBOutlet 图像。 tableView:cellForRowAtIndexPath: 中的 TableView 委托(delegate):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。它最初有效，但不幸的是，当用户尝试点赞帖子时，出于某种原因，这会扰乱点赞按钮的行为。

更新:这里不需要 prepareForResuse() 作为答案之一的建议。

// 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 post feed viewcontroller 文件的 likeButtonTapped 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.")

                }

            })

        } 

} 

最佳答案

在您的情况下不需要使用 prepareForReuse 方法，您可以通过以下方式替换 cellForRowAtIndexPath 中的代码来实现:

// Set likeButton image to the default unfilled version
var image = UIImage(named: "likeButtonUnfilled")

// 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
         image = UIImage(named: "likeButtonFilled") as UIImage!
         break // Terminate loop when we found required object
    }
}
self.likeButton.setImage(image, forState: UIControlState.Normal)

为了使上述代码正常工作，还需要您在完成喜欢/不喜欢操作时相应地更新您的 currUserLikeObjects，并更新特定的 tableview 单元格以反射(reflect)屏幕上的修改。

关于ios - 可重复使用的表格 View 单元格中的 UIButton 图像切换问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35610373/