印象里，iOS除了使用Home键，并不能主动退出，今天中午订餐的时候，打开了许久没用的饿了么，意外发现，饿了么有不同意并退出的功能，百度尝试了一下，只是很简单的一段代码而已，效果和数据安全且不论，但是确实可以实现退出App。
退出App的三种方法，exit(1)、abort()、assert(0)
源码在底部：
1.exit(1)
附加了关闭打开文件与返回状态码给执行环境,并调用你用atexit注册的返回函数
iOS终止函数exit
调用exit会让用户感觉程序崩溃了，不会有按Home键返回时的平滑过渡和动画效果；另外，使用exit可能会丢失数据，因为调用exit并不会调用-applicationWillTerminate:方法和UIApplicationDelegate方法
2.abort()
解除进程对SIGABRT信号的阻止，然后向调用进程发送该信号，abort()可以导致进程的异常终止，除非SIGABRT信号被处理，可以通过NSSetUncaughtExceptionHandler来捕捉，从而可以做到从容的退出App，参考资料如下：RunLoop总结：RunLoop的应用场景（五）阻止App崩溃一次
捕捉并处理异常效果图
3.assert(0)
Assert断言
当程序检查到断言条件为false时，触发断言，而后程序崩溃，可在日志中读到相关的过程，在正式发布的Release版中，一般都是会禁用断言功能的；
assert(0)同样可以用捕捉处理abort()的方式进行捕捉，因为assert最终还是会调用abort()产生SIGABRT信号来终止App
总结
OC并不提供正常退出iOSApp的API，上面三种方式虽然可以退出App，但不符合苹果一贯的友好风格，所以也是有可能上架悲剧。
源码：
//
// AppExitTestViewController.m
// Modulator
//
// Created by M君 on 25/06/2018.
// Copyright © 2018 huihaiweishi. All rights reserved.
//
#import "AppExitTestViewController.h"
typedef NS_ENUM(NSUInteger, AppExitTestTag) {
AppExitTestTag_Exit = 100,
AppExitTestTag_Abort,
AppExitTestTag_Assert,
};
@interface AppExitTestViewController ()
@end
@implementation AppExitTestViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
self.view.backgroundColor = [UIColor lightGrayColor];
//
UIButton *exitBtn = [UIButton buttonWithType:UIButtonTypeCustom];
exitBtn.frame = CGRectMake(0, 0, 100, 60);
exitBtn.layer.borderWidth = 1.0;
exitBtn.layer.borderColor = [UIColor whiteColor].CGColor;
exitBtn.tag = AppExitTestTag_Exit;
exitBtn.backgroundColor = [UIColor lightGrayColor];
[exitBtn setTitle:@"Exit" forState:UIControlStateNormal];
[exitBtn addTarget:self action:@selector(onAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:exitBtn];
//
UIButton *abortBtn = [UIButton buttonWithType:UIButtonTypeCustom];
abortBtn.frame = CGRectMake(0, 0, 100, 60);
abortBtn.layer.borderWidth = 1.0;
abortBtn.layer.borderColor = [UIColor whiteColor].CGColor;
abortBtn.tag = AppExitTestTag_Abort;
abortBtn.backgroundColor = [UIColor lightGrayColor];
[abortBtn setTitle:@"Abort" forState:UIControlStateNormal];
[abortBtn addTarget:self action:@selector(onAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:abortBtn];
//
UIButton *assertBtn = [UIButton buttonWithType:UIButtonTypeCustom];
assertBtn.frame = CGRectMake(0, 0, 100, 60);
assertBtn.layer.borderWidth = 1.0;
assertBtn.layer.borderColor = [UIColor whiteColor].CGColor;
assertBtn.tag = AppExitTestTag_Assert;
assertBtn.backgroundColor = [UIColor lightGrayColor];
[assertBtn setTitle:@"Assert" forState:UIControlStateNormal];
[assertBtn addTarget:self action:@selector(onAction:) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:assertBtn];
//
abortBtn.center = self.view.center;
exitBtn.center = CGPointMake(abortBtn.centerX, abortBtn.top - exitBtn.height/2 - 10);
assertBtn.center = CGPointMake(abortBtn.centerX, abortBtn.bottom + exitBtn.height/2 + 10);
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#pragma mark - action
- (void)onAction:(UIButton *)btn
{
NSString *title = @"Terminate the App";
NSString *message = [NSString stringWithFormat:@"Will Terminate the App with Button: %@",btn.titleLabel.text];
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:title message:message preferredStyle:UIAlertControllerStyleAlert];
[alertController addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleDefault handler:nil]];
[alertController addAction:[UIAlertAction actionWithTitle:@"Confirm" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
AppExitTestTag tag = (AppExitTestTag)btn.tag;
switch (tag) {
case AppExitTestTag_Exit:
exit(1);
break;
case AppExitTestTag_Abort:
abort();
break;
case AppExitTestTag_Assert:
assert(0);
break;
default:
break;
}
}]];
[self presentViewController:alertController animated:YES completion:nil];
}
@end
