Swift 3 - 第一个单元格已展开的可扩展表格视图单元格 [英] Swift 3 - Expandable Table View Cells with first cell already expanded

问题描述

我使用的是 Swift 3.

我已按照本教程获取它，以便我可以点击表格视图单元格，该单元格将展开以显示更多信息.

但是我如何才能使第一个单元格已经展开?

感谢您的帮助.

解决方案

我觉得你没有完全理解你自己的代码，但既然你确实在你的问题上付出了很多努力，我会给你一个提示.

在你的 UITableViewController 顶部的某个地方初始化 selectedIndexPath ，它应该看起来像

var selectedIndexPath: IndexPath?

您可以将其设置为这样的默认值

var selectedIndexPath: IndexPath?= IndexPath(行:0，部分:0)

所以 (row: 0, section: 0) 处的单元格将默认展开.

I am using Swift 3.

I've followed this tutorial to get it so that I can tap on a table view cell which will expand revealing more information.

https://www.youtube.com/watch?v=VWgr_wNtGPM&t=294s

My question is: how do I do it so that the first cell is expanded when the view loads already (i.e. the user doesn't have to click to see that cell expand) but all other behavior remains the same (e.g. if it's clicked again, it de-collapses)?

UITableViewCell:

import UIKit

class ResultsCell: UITableViewCell {

    @IBOutlet weak var introPara : UITextView!
    @IBOutlet weak var section_heading : UILabel!

    class var expandedHeight : CGFloat { get { return 200.0 } }
    class var defaultHeight : CGFloat { get { return 44.0 } }
    var frameAdded = false


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

    override func awakeFromNib() {
        super.awakeFromNib()
        section_heading.translatesAutoresizingMaskIntoConstraints = false
    }

    func checkHeight() {
        introPara.isHidden = (frame.size.height < ResultsCell.expandedHeight)
    }

    func watchFrameChanges() {
        if(!frameAdded) {
            addObserver(self, forKeyPath: "frame", options: .new, context: nil)
            checkHeight()
        }
    }

    func ignoreFrameChanges() {
        if(frameAdded){
            removeObserver(self, forKeyPath: "frame")
        }
    }

    deinit {
        print("deinit called");
        ignoreFrameChanges()
    }

    // when our frame changes, check if the frame height is appropriate and make it smaller or bigger depending
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "frame" {
            checkHeight()
        }
    }

}

UITableViewController

// class declaration and other methods above here...

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

// number of rows in the table view
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return section_heading.count
}

// return the actual view for the cell
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let resultcell = tableView.dequeueReusableCell(withIdentifier: "resultCellTemplate", for: indexPath) as! ResultsCell
    resultcell.section_heading.text = section_heading[indexPath.row]
    resultcell.introPara.attributedText = contentParagraphs[indexPath.row]

    return resultcell
}

// when a cell is clicked
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let previousIndexPath = selectedIndexPath

    // the row is already selected, then we want to collapse the cell
    if indexPath == selectedIndexPath {
        selectedIndexPath = nil
    } else { // otherwise, we expand that cell
        selectedIndexPath = indexPath
    }

    var indexPaths : Array<IndexPath> = []

    // only add a previous one if it exists
    if let previous = previousIndexPath {
        indexPaths.append(previous)
    }
    if let current = selectedIndexPath {
        indexPaths.append(current)
    }

    // reload the specific rows
    if indexPaths.count > 0 {
        tableView.reloadRows(at: indexPaths, with: .automatic)
    }
}

override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    (cell as! ResultsCell).watchFrameChanges()
}

override func tableView(_ tableView: UITableView, didEndDisplaying cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    (cell as! ResultsCell).ignoreFrameChanges()

}

override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
    if indexPath == selectedIndexPath {
        return ResultsCell.expandedHeight
    } else {
        return ResultsCell.defaultHeight
    }
}

So this works as intended.

But how do I make it so that the first cell is already expanded?

Thanks for your help.

解决方案

I feel like you do not fully understand your own code but since you did put a lot of effort into your question I will give you a hint.

In your UITableViewController somewhere at the top you initialise selectedIndexPath which should look something like

var selectedIndexPath: IndexPath?

You can set that to a default value like this

var selectedIndexPath: IndexPath? = IndexPath(row: 0, section: 0)

So cell at (row: 0, section: 0) will expand on default.

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