Java是有try catch 的，提前驗證正確性。iOS也有嘛，但是隻能捕獲一些陣列越界，資料型別不對之類的異常，Xcode不識別，那麼就崩潰，閃退了。
提高使用者體驗，不閃退，從我開始，哈哈，特簡單的嘛

@try {
         //執行的程式碼，如果異常,就會丟擲，程式不繼續執行啦
    } @catch (NSException *exception) {
        //捕獲異常
    } @finally {
        //這裡一定執行，無論你異常與否
    }
   邏輯怎麼寫，就看你了，看專案了

但是比如野指標或者記憶體溢位，就不行了。so這裡可以捕獲這些異常的

上程式碼

定義一個物件
.h裡面

#import <Foundation/Foundation.h>

#import <UIKit/UIKit.h>

@interface UncaughtExceptionHandler : NSObject
{
    BOOL dismissed;
}
@end
void HandleException(NSException *exception);
void SignalHandler(int signal);
void InstallUncaughtExceptionHandler(void);

.m 裡面

#import "UncaughtExceptionHandler.h"
#import <UIKit/UIKit.h>
#include <libkern/OSAtomic.h>
#include <execinfo.h>
#import "AppDelegate.h"

NSString *const UncaughtExceptionHandlerSignalExceptionName [email protected]"UncaughtExceptionHandlerSignalExceptionName";
NSString *const
 
 UncaughtExceptionHandlerSignalKey [email protected]"UncaughtExceptionHandlerSignalKey";
NSString *const UncaughtExceptionHandlerAddressesKey [email protected]"UncaughtExceptionHandlerAddressesKey";

volatile int32_t UncaughtExceptionCount =0;
const int32_t UncaughtExceptionMaximum =10;

const NSInteger UncaughtExceptionHandlerSkipAddressCount =4;
const NSInteger UncaughtExceptionHandlerReportAddressCount =5;

@implementation UncaughtExceptionHandler
+ (NSArray *)backtrace {// 程式崩潰2(程式崩潰第二步走的方法)
    void* callstack[128];
    int frames =backtrace(callstack, 128);
    char **strs =backtrace_symbols(callstack, frames);
    int i;
    NSMutableArray *backtrace = [NSMutableArray arrayWithCapacity:frames];
    for (i = UncaughtExceptionHandlerSkipAddressCount ; i <UncaughtExceptionHandlerSkipAddressCount +UncaughtExceptionHandlerReportAddressCount; i++){
        [backtrace addObject:[NSString stringWithUTF8String:strs[i]]];
    }
    free(strs);
    return backtrace;
}

- (void)alertView:(UIAlertView *)anAlertView clickedButtonAtIndex:(NSInteger)anIndex {
    if (anIndex ==0){
        dismissed =YES;
    }else if(anIndex==1) {
        NSLog(@"ssssssss");
    }
}

- (void)validateAndSaveCriticalApplicationData {
    // 崩潰攔截可以做的事,寫在這個方法也是極好的
    NSLog(@"崩潰了");
    UIAlertController * alert = [UIAlertController alertControllerWithTitle:@"溫馨提示"  message:@"開啟" preferredStyle:UIAlertControllerStyleAlert];

    UIAlertAction * cancelAction = [UIAlertAction actionWithTitle:@"確定" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {

    }];

    [alert addAction:cancelAction];

    UIViewController * rootViewController = [[[UIApplication sharedApplication] keyWindow] rootViewController];
    [rootViewController presentViewController:alert animated:YES completion:^{

    }];
}
// 程式崩潰3(程式崩潰是第三進入的方法)
- (void)handleException:(NSException *)exception {
    [self validateAndSaveCriticalApplicationData];
    NSString *message = [NSString stringWithFormat:NSLocalizedString(@"如果點選繼續，程式有可能會出現其他的問題，建議您還是點選退出按鈕並重新開啟\n\n"@"異常原因如下:\n%@\n%@",nil),[exception reason],[[exception userInfo] objectForKey:UncaughtExceptionHandlerAddressesKey]];
    UIAlertView *alert =[[UIAlertView alloc]initWithTitle:NSLocalizedString(@"抱歉，程式出現了異常",nil)
                                                 message:message
                                                delegate:self
                                       cancelButtonTitle:NSLocalizedString(@"退出",nil)
                                       otherButtonTitles:NSLocalizedString(@"繼續",nil), nil];

    NSLog(@"異常顯示了");

    [alert show];
    UIAlertAction *act1 = [UIAlertAction actionWithTitle:@"確定" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

    }];
    UIAlertController *vc = [UIAlertController alertControllerWithTitle:@"異常啦" message:nil preferredStyle:UIAlertControllerStyleAlert];
    [vc addAction:act1];
    UIViewController *rootViewController = [[[UIApplication sharedApplication] keyWindow] rootViewController];
    [rootViewController presentViewController:vc animated:YES completion:nil];

    CFRunLoopRef runLoop = CFRunLoopGetCurrent();
    CFArrayRef allModes = CFRunLoopCopyAllModes(runLoop);

    while (!dismissed) {
        for (NSString *mode in (__bridge NSArray *)allModes) {
            CFRunLoopRunInMode((CFStringRef)mode,0.001, false);
        }
    }

    CFRelease(allModes);
    NSSetUncaughtExceptionHandler(NULL);
    signal(SIGABRT,SIG_DFL);
    signal(SIGILL,SIG_DFL);
    signal(SIGSEGV,SIG_DFL);
    signal(SIGFPE,SIG_DFL);
    signal(SIGBUS,SIG_DFL);
    signal(SIGPIPE,SIG_DFL);

    if ([[exception name] isEqual:UncaughtExceptionHandlerSignalExceptionName]) {
        kill(getpid(), [[[exception userInfo] objectForKey:UncaughtExceptionHandlerSignalKey]intValue]);
    }else{
        [exception raise];
    }
}

@end

void HandleException(NSException *exception) {
    int32_t exceptionCount =OSAtomicIncrement32(&UncaughtExceptionCount);
    if (exceptionCount >UncaughtExceptionMaximum) {
        return;
    }

    NSArray *callStack = [UncaughtExceptionHandler backtrace];
    NSMutableDictionary *userInfo =[NSMutableDictionary dictionaryWithDictionary:[exception userInfo]];[userInfo setObject:callStack forKey:UncaughtExceptionHandlerAddressesKey];

    [[[UncaughtExceptionHandler alloc] init]performSelectorOnMainThread:@selector(handleException:)withObject:
     [NSException exceptionWithName:[exception name] reason:[exception reason] userInfo:userInfo]waitUntilDone:YES];
}

void SignalHandler(int signal) {

    int32_t exceptionCount =OSAtomicIncrement32(&UncaughtExceptionCount);
    if (exceptionCount >UncaughtExceptionMaximum) {
        return;
    }

    NSMutableDictionary *userInfo =[NSMutableDictionary dictionaryWithObject:[NSNumber numberWithInt:signal] forKey:UncaughtExceptionHandlerSignalKey];

    NSArray *callStack = [UncaughtExceptionHandler backtrace];
    [userInfo setObject:callStack forKey:UncaughtExceptionHandlerAddressesKey];

    [[[UncaughtExceptionHandler alloc] init]performSelectorOnMainThread:@selector(handleException:)withObject:[NSException exceptionWithName:UncaughtExceptionHandlerSignalExceptionName reason:[NSString stringWithFormat:NSLocalizedString(@"Signal %d was raised.",nil),signal]userInfo:
                                                                                                              [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:signal]forKey:UncaughtExceptionHandlerSignalKey]]waitUntilDone:YES];
}

void InstallUncaughtExceptionHandler(void) {
    NSSetUncaughtExceptionHandler(&HandleException);
    signal(SIGHUP, SignalHandler);//本訊號在使用者終端連線(正常或非正常)結束時發出, 通常是在終端的控制程序結束時, 通知同一session內的各個作業
    signal(SIGINT, SignalHandler);//程式終止(interrupt)訊號, 在使用者鍵入INTR字元(通常是Ctrl-C)時發出，用於通知前臺程序組終止程序。
    signal(SIGQUIT, SignalHandler);//類似於一個程式錯誤訊號。


    signal(SIGABRT,SignalHandler);//呼叫abort函式生成的訊號。
    signal(SIGILL,SignalHandler);//用來立即結束程式的執行. 本
    signal(SIGSEGV,SignalHandler);//試圖訪問未分配給自己的記憶體, 或試圖往沒有寫許可權的記憶體地址寫資料.
    signal(SIGFPE,SignalHandler);//在發生致命的算術運算錯誤時發出.
    signal(SIGBUS,SignalHandler);//訪問不屬於自己儲存空間或只讀儲存空間
    signal(SIGPIPE,SignalHandler);//管道破裂。
}

之後AppDelegate.h裡面

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
              NSSetUncaughtExceptionHandler(&UncaughtExceptionHandler);
    return YES;    
}

這樣就可以啦