Open Whatsapp on a particular number in swift

For swift 4.2 / Swift 5

func openWhatsapp(){
    let urlWhats = "whatsapp://send?phone=(mobile number with country code)"
    if let urlString = urlWhats.addingPercentEncoding(withAllowedCharacters: CharacterSet.urlQueryAllowed){
        if let whatsappURL = URL(string: urlString) {
            if UIApplication.shared.canOpenURL(whatsappURL){
                if #available(iOS 10.0, *) {
                    UIApplication.shared.open(whatsappURL, options: [:], completionHandler: nil)
                } else {
                    UIApplication.shared.openURL(whatsappURL)
                }
            }
            else {
                print("Install Whatsapp")
            }
        }
    }
}

For Swift 2.0

let urlWhats = "whatsapp://send?phone=(mobile number with country code)"
        if let urlString = urlWhats.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet()){
            if let whatsappURL = NSURL(string: urlString) {
                if UIApplication.sharedApplication().canOpenURL(whatsappURL){
                    UIApplication.sharedApplication().openURL(whatsappURL)
                }
                else {
                    print("Install Whatsapp")
                }
            }
        }

Note: Add url scheme in info.plist

<key>LSApplicationQueriesSchemes</key>
 <array>
    <string>whatsapp</string>
 </array>

Its possible You can send messages to Specfic user.

Direct app chat url open

let urlWhats = "whatsapp://send?phone=+919789384445&abid=12354&text=Hello"
    if let urlString = urlWhats.addingPercentEncoding(withAllowedCharacters: NSCharacterSet.urlQueryAllowed) {
        if let whatsappURL = URL(string: urlString) {
            if UIApplication.shared.canOpenURL(whatsappURL!) {
                UIApplication.shared.openURL(whatsappURL!)
            } else {
                print("Install Whatsapp")
            }
        }
    }

Note:Country code (Ex:+91) is mandatory to open mobile number Chat

WebUrl Link open Chat

 let whatsappURL = URL(string: "https://api.whatsapp.com/send?phone=9512347895&text=Invitation")
    if UIApplication.shared.canOpenURL(whatsappURL) {
        UIApplication.shared.open(whatsappURL, options: [:], completionHandler: nil)
    }

Check below link,

https://www.whatsapp.com/faq/en/general/26000030

Note: Add url scheme in info.plist

<key>LSApplicationQueriesSchemes</key>
 <array>
    <string>whatsapp</string>
 </array>