NSTimer don't stop when I present another viewcontroller - ios

Question

I have a viewController1 setting a timer.
When the timer countdown to 0, I'll present viewController2.
The timer also keeps going, although I call the timer function invalidate
Then I mark present viewcontroller code, it seems stop correctly.
//ViewController2 *vc = [[ViewController2 alloc] init];
//[self presentViewController:vc animated:false completion:nil];
What's wrong with code?
#import "ViewController.h"
#import <WebKit/WebKit.h>
#import "ViewController2.h"
#interface ViewController ()<WKScriptMessageHandler, WKNavigationDelegate,WKUIDelegate>
#property (nonatomic,strong) WKWebView* webView;
#property (nonatomic, strong) WKWebViewConfiguration * webConfig;
#property (nonatomic, strong) NSTimer *timer;
#property (nonatomic) int count;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.webView = [[WKWebView alloc] initWithFrame:self.view.frame configuration:[self createWKWebApp]];
[self.view addSubview: self.webView];
[self.webView.configuration.preferences setValue:#YES forKey:#"allowFileAccessFromFileURLs"];
self.webView.scrollView.bounces = NO;
[self.webView setContentMode:UIViewContentModeScaleAspectFit];
self.webView.navigationDelegate = self;
self.webView.UIDelegate = self;
NSURL *url = [NSURL URLWithString:#"https://www.google.com.tw"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[self.webView loadRequest:request];
self.count = 5;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(timerFired) userInfo:nil repeats:YES];
}
-(void)timerFired {
NSLog(#"===) self.count : %d", self.count);
if (self.count == 0) {
ViewController2 *vc = [[ViewController2 alloc] init];
[self presentViewController:vc animated:false completion:^{
[self.timer invalidate];
self.timer = nil;
}];
} else {
self.count -= 1;
}
}
- (WKWebViewConfiguration *)createWKWebApp {
WKWebViewConfiguration *config = [[WKWebViewConfiguration alloc] init];
WKUserContentController *userContent = [[WKUserContentController alloc] init];
config.userContentController = userContent;
return config;
}
- (void)userContentController:(WKUserContentController*)userContentController didReceiveScriptMessage:(WKScriptMessage*)message {
}
#end

Answer 1

Before present a ViewController, stop the timer
[self.timer invalidate];
self.timer = nil;
ViewController2 *vc = [[ViewController2 alloc] init];
[self presentViewController:vc animated:false completion:nil];

Answer 2

Invalidate the timer in viewWillDisappear delegate method and tigger again whenever view will appear again.