我有一个函数,里面有2个if语句。代码:
func pictureFromFirebase(loginMethod: Int)
{
if loginMethod == 0 //FB
{
var profilePic = FBSDKGraphRequest(graphPath: "me/picture", parameters: ["height":300, "width":300, "redirect":false], httpMethod: "GET")
let profilePicRef = storageRef.child((user?.uid)!+"/profile_pic.jpg")
profilePicRef.data(withMaxSize: 1 * 1024 * 1024) { data, error in
if let error = error {
// Uh-oh, an error occurred!
} else {
if (data != nil)
{
print("no need to download image from facebook")
self.profileImage.image = UIImage (data: data!)
}
}
}
if profileImage.image == nil
{
print("downloading image from facebook")
profilePic?.start(completionHandler: {(_ connection, _ result, _ error) -> Void in
if (error == nil)
{
if let dictionary = result as? [String:Any], let data = dictionary["data"] as? [String:Any],
let urlPic = data["url"] as? String {
if let imageData = NSData(contentsOf: NSURL(string: urlPic)! as URL)
{
let uploadTask = profilePicRef.put(imageData as Data, metadata: nil){
metadata, error in
if (error == nil)
{
let downloadUrl = metadata!.downloadURL
}
else
{
print("error in downloading image")
}
}
self.profileImage.image = UIImage(data: imageData as Data)
}
}
}
})
}
}
}
只有在触发此功能时才会调用它:
FIRAuth.auth()?.addStateDidChangeListener() { (auth, user) in
print("called")
if let user = user {
if(activeUser != user){
let name = user.displayName
self.profileName.text = name
self.pictureFromFirebase(loginMethod: 0)
}
}
这是调试的正常输出,当我已经设置了图像时,不需要从Facebook下载图像:
-called - 从Facebook下载图像 -called - 从Facebook下载图像 - 无需从Facebook下载图像 - 无需从Facebook下载图片
当我删除整个第二个if语句时,这是调试的输出(如果profileImage.image == nil):
-called -called - 无需从Facebook下载图像 - 无需从Facebook下载图片
从我所看到的,除了函数被调用两次也是错误的,第二个语句在第一个语句执行之前被调用。由于第一个语句在设置profileImage之前需要一段时间,因此当第二个if语句检查此值时它为nil。我怎样才能确保不再发生这种情况?谢谢。
答案 0 :(得分:2)
异步方法!在继续下一步之前,您必须等待完成。
将第二个块放在第一个完成处理程序中 - 就像这样
func pictureFromFirebase(loginMethod: Int)
{
if loginMethod == 0 //FB
{
var profilePic = FBSDKGraphRequest(graphPath: "me/picture", parameters: ["height":300, "width":300, "redirect":false], httpMethod: "GET")
let profilePicRef = storageRef.child((user?.uid)!+"/profile_pic.jpg")
profilePicRef.data(withMaxSize: 1 * 1024 * 1024) { data, error in
if let error = error {
// Uh-oh, an error occurred!
// but we don't need to do anything yet. Try to download the profile pic
}
if (data != nil)
{
print("no need to download image from facebook")
self.profileImage.image = UIImage (data: data!)
}
else
{
// THIS IS THE BLOCK THAT HAS BEEN MOVED
// WHICH WILL NOW BE EXECUTED IN TWO CONDITIONS -
// 1. AN ERROR IN THE DOWNLOAD
// 2. NO PROFILE PIC AVAILABLE
print("downloading image from facebook")
profilePic?.start(completionHandler: {(_ connection, _ result, _ error) -> Void in
if (error == nil)
{
if let dictionary = result as? [String:Any], let data = dictionary["data"] as? [String:Any],
let urlPic = data["url"] as? String {
if let imageData = NSData(contentsOf: NSURL(string: urlPic)! as URL)
{
let uploadTask = profilePicRef.put(imageData as Data, metadata: nil){
metadata, error in
if (error == nil)
{
let downloadUrl = metadata!.downloadURL
}
else
{
print("error in downloading image")
}
}
self.profileImage.image = UIImage(data: imageData as Data)
}
}
}
})
}
}
}
}