PFQueryTableViewController分页不适用于heightForRowAtIndexPath

问题描述：

当我设置分页将不起作用时，我正在将Swift与parse.com框架以及PFQueryTableViewController一起使用.如果数据库的行数少于objectPerPage中设置的行数，则工作正常，但如果行数更多，则当我运行应用程序时，它会继续显示加载屏幕，而没有下载任何内容，当我执行刷卡刷新"时，崩溃错误

I am using parse.com framework with Swift and in PFQueryTableViewController when I set the pagination it won't work. If the DB has less rows than the number set in objectPerPage it works fine, but if there are more rows and when I run the app it keeps showing the loading screen and nothing is downloaded, when I do "swipe as refresh" it crash as Error

*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 5 beyond bounds [0 .. 4]

ImagesTableViewController.swift

import UIKit
import Parse
import ParseUI
import Bolts

class ImagesTableViewController: PFQueryTableViewController {
@IBAction func unwindToSegue (segue : UIStoryboardSegue) {}

// Initialise the PFQueryTable tableview
override init(style: UITableViewStyle, className: String!) {
    super.init(style: style, className: className)
}

required init(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)

    // Configure the PFQueryTableView
    self.parseClassName = "Image"
    self.pullToRefreshEnabled = true
    self.paginationEnabled = true
    self.objectsPerPage = 5

}

// Define the query that will provide the data for the table view
override func queryForTable() -> PFQuery {
    var query = PFQuery(className: "Image")
    query.whereKey("deleted", notEqualTo: 1)
    query.orderByDescending("createdAt")
    return query
}

//override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath, object: PFObject?) -> PFTableViewCell {

    var cell = tableView.dequeueReusableCellWithIdentifier("ImageCell") as! ImageTVCell!
    if cell == nil {
        cell = ImageTVCell(style: UITableViewCellStyle.Default, reuseIdentifier: "ImageCell")
    }

    // Extract values from the PFObject to display in the table cell HEADLINE
    if let caption = object?["caption"] as? String {
        cell?.headlineLabel?.text = caption
    }

    // Display image
    var initialThumbnail = UIImage(named: "question")
    cell.postImageView.image = initialThumbnail
    if let thumbnail = object?["image"] as? PFFile {
        cell.postImageView.file = thumbnail
        cell.postImageView.loadInBackground()
    }

    return cell
}

// if I remove this code pagination work but the cell height is wrong
override func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
    return calculateHeightForRowAtIndexPath(indexPath)
}


func calculateHeightForRowAtIndexPath(indexPath: NSIndexPath) -> CGFloat {
    if let ratio = objectAtIndexPath(indexPath)?["aspect"] as? Float {
        println("Ratio: \(ratio)")
        return tableView.bounds.size.width / CGFloat(ratio)
    } else {
        return 50.0
    }
}


@IBAction func addNewPhotoButton(sender: UIBarButtonItem) {
    self.tabBarController?.tabBar.hidden = true
    self.performSegueWithIdentifier("showUploadNewImage", sender: self)
}

}

答

之所以会出现此问题，是因为UITableViewDataSource中方法tableView:numberOfRowsInSection的PFQueryTableViewController实现.我已经从 GitHub存储库复制/粘贴包含PFQueryTableViewController.m

This problem occurs because of PFQueryTableViewController's implementation of the method tableView:numberOfRowsInSection from the UITableViewDataSource. I've copy/pasted it from the GitHub repo containing PFQueryTableViewController.m

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSInteger count = [self.objects count];
    if ([self _shouldShowPaginationCell]) {
        count += 1;
    }
    return count;
}

它只是返回要显示的对象数(这很有意义)，但是如果启用了分页，则需要显示一个额外的单元格.这意味着您必须手动创建带有加载更多数据"或类似内容的文本的另一个单元，这将触发刷新.

It simply returns the count of objects to display (which makes sense), but if pagination is enabled, then it requires for an extra cell to be shown. This means you have to manually created another cell with the text "Load more data" or something like that, which would trigger a refresh.

克服此问题的一种方法就是简单地使用以下内容覆盖tableView:numberOfRowsInSection自己:

A way to overcome this is simply by overriding tableView:numberOfRowsInSection yourself with the following:

override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return self.objects!.count
}

更新1

上一个答案中没有内置的Parse分页按钮

The prebuilt Parse pagination button was gone in previous answer

使用以下代码段计算单元格的高度，以显示预构建的Parse分页按钮

Use the following code snippet for calculating the height of the cells to display the prebuilt Parse pagination button

func calculateHeightForRowAtIndexPath(indexPath: NSIndexPath) -> CGFloat {
    // Special case for pagination, using the pre-built one by Parse
    if (indexPath.row >= objects!.count) { return 50.0 }

    // Determines the height if an image ratio is present
    if let ratio = objectAtIndexPath(indexPath)?["aspect"] as? Float {
        println("Ratio: \(ratio)")
        return tableView.bounds.size.width / CGFloat(ratio)
    } else {
        return 50.0
    }
}

PFQueryTableViewController分页不适用于heightForRowAtIndexPath

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