在展开可选值 dispatch-async 时意外发现 nil
unexpectedly found nil while unwrapping an Optional value dispatch-async
我正在尝试在点击 postVC 上的按钮加载数据并导航到 guestVC 后从 Parse 服务器加载数据。它工作正常,但有时应用程序开始崩溃……不知道为什么?我收到致命错误:在展开可选值时意外发现 nil ...任何和所有方向或帮助将不胜感激。谢谢!
import UIKit
import Parse
var postuuid = [String]()
class postVC: UITableViewController {
//postVC button click function
//clicked username button from post
@IBAction func usernameBtn_click(sender: AnyObject) {
let i = sender.layer.valueForKey("index") as! NSIndexPath
let cell = tableView.cellForRowAtIndexPath(i) as! postCell
// if user tapped on himself go home, else go guest
if cell.usernameBtn.titleLabel?.text == PFUser.currentUser()?.username {
let home = self.storyboard?.instantiateViewControllerWithIdentifier("homeVC") as! homeVC
self.navigationController?.pushViewController(home, animated: true)
} else {
let guest = self.storyboard?.instantiateViewControllerWithIdentifier("guestVC") as! guestVC
self.navigationController?.pushViewController(guest, animated: true)
}
}
// guestVC relevant code
import UIKit
import Parse
var guestname = [String]()
class guestVC: UICollectionViewController {
var uuidArray = [String]()
var picArray = [PFFile]()
// posts loading function
func loadPosts() {
let query = PFQuery(className: "posts")
// app keeps crashing in line below when I try to load data to guestVC
query.whereKey("username", equalTo: guestname.last!)
query.limit = self.page
query.findObjectsInBackgroundWithBlock( { (objects:[PFObject]?, error:NSError?) -> Void in
if error == nil {
self.uuidArray.removeAll(keepCapacity: false)
self.picArray.removeAll(keepCapacity: false)
for object in objects! {
self.uuidArray.append(object.valueForKey("uuid") as! String)
self.picArray.append(object.valueForKey("pic") as! PFFile)
}
self.collectionView?.reloadData()
} else {
print(error!.localizedDescription)
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
// code here will be executed as the main queue
})
})
}
在添加或附加之前,检查字典键值是否有效。检查 'uuid' 或 'pic' 键是否在字典中有值。如果有那么 add/append.
您在代码中使用大量感叹号强制展开可选值,这是一个坏习惯。
例如,您可以通过以下方式安全地解包 guestname.last:
guard let lastItem = guestname.last else {
// do something else
return
}
query.whereKey("username", equalTo: lastItem)
我正在尝试在点击 postVC 上的按钮加载数据并导航到 guestVC 后从 Parse 服务器加载数据。它工作正常,但有时应用程序开始崩溃……不知道为什么?我收到致命错误:在展开可选值时意外发现 nil ...任何和所有方向或帮助将不胜感激。谢谢!
import UIKit
import Parse
var postuuid = [String]()
class postVC: UITableViewController {
//postVC button click function
//clicked username button from post
@IBAction func usernameBtn_click(sender: AnyObject) {
let i = sender.layer.valueForKey("index") as! NSIndexPath
let cell = tableView.cellForRowAtIndexPath(i) as! postCell
// if user tapped on himself go home, else go guest
if cell.usernameBtn.titleLabel?.text == PFUser.currentUser()?.username {
let home = self.storyboard?.instantiateViewControllerWithIdentifier("homeVC") as! homeVC
self.navigationController?.pushViewController(home, animated: true)
} else {
let guest = self.storyboard?.instantiateViewControllerWithIdentifier("guestVC") as! guestVC
self.navigationController?.pushViewController(guest, animated: true)
}
}
// guestVC relevant code
import UIKit
import Parse
var guestname = [String]()
class guestVC: UICollectionViewController {
var uuidArray = [String]()
var picArray = [PFFile]()
// posts loading function
func loadPosts() {
let query = PFQuery(className: "posts")
// app keeps crashing in line below when I try to load data to guestVC
query.whereKey("username", equalTo: guestname.last!)
query.limit = self.page
query.findObjectsInBackgroundWithBlock( { (objects:[PFObject]?, error:NSError?) -> Void in
if error == nil {
self.uuidArray.removeAll(keepCapacity: false)
self.picArray.removeAll(keepCapacity: false)
for object in objects! {
self.uuidArray.append(object.valueForKey("uuid") as! String)
self.picArray.append(object.valueForKey("pic") as! PFFile)
}
self.collectionView?.reloadData()
} else {
print(error!.localizedDescription)
}
dispatch_async(dispatch_get_main_queue(), { () -> Void in
// code here will be executed as the main queue
})
})
}
在添加或附加之前,检查字典键值是否有效。检查 'uuid' 或 'pic' 键是否在字典中有值。如果有那么 add/append.
您在代码中使用大量感叹号强制展开可选值,这是一个坏习惯。 例如,您可以通过以下方式安全地解包 guestname.last:
guard let lastItem = guestname.last else {
// do something else
return
}
query.whereKey("username", equalTo: lastItem)