AppDelegate對於做ios開發的朋友可能並不陌生了，AppDelegate裡面有許多的函數可以讓我們直接的調用了，我們下面來看關於AppDelegate函數的一些含義吧．

在大家剛接觸iOS的時候，每次生成一個項目的時候，系統都會自動生成一個AppDelegate的類，其中各種函數，對初學者的我來說，真是一點摸不著頭腦，也不知道如何運用，今天就給大家來講講AppDelegate的一些用法和含義。

來看看AppDelegate.m文件中的一些函數的含義吧。

//
//  AppDelegate.m
//
//
//  Created by Kenshin Cui on 14-2-23.
//  Copyright (c) 2014年 Kenshin Cui. All rights reserved.
//
 
#import "AppDelegate.h"
 
@implementation AppDelegate
 
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    return YES;
}
 
- (void)applicationWillResignActive:(UIApplication *)application
{
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
 
- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}
 
- (void)applicationWillEnterForeground:(UIApplication *)application
{
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}
 
- (void)applicationDidBecomeActive:(UIApplication *)application
{
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}
 
- (void)applicationWillTerminate:(UIApplication *)application
{
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}
 
@end
其實說白了，這個類中定義了應用程序生命周期中各個事件的執行方法：

– (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;程序啟動之後執行，只有在第一次程序啟動後才執行，以後不再執行；

– (void)applicationWillResignActive:(UIApplication *)application;程序將要被激活時執行，程序激活用戶才能操作；

– (void)applicationDidEnterBackground:(UIApplication *)application;程序進入後台後執行，注意進入後台時會先失去焦點再進入後台；

– (void)applicationWillEnterForeground:(UIApplication *)application;程序將要進入前台時執行；

– (void)applicationDidBecomeActive:(UIApplication *)application;程序被激活後執行，注意程序被激活時會先進入前台再被激活；

– (void)applicationWillTerminate:(UIApplication *)application;程序在終止時執行，包括正常終止或異常終止，例如說一個應用程序在後台程序占用太多內存這時會意外終止調用此方法；

這裡所有函數的含義也就搞清楚了，我習慣是把一些整個程序都用到的一些屬性或函數，直接寫在- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;這個函數裡面，這樣我也省下了不少時間，其他的函數的運用，大家可以敞開胸懷的去暢想了。