iOS中AppDelegate的各函數的含義

在大家剛接觸iOS的時候，每次產生一個項目的時候，系統都會自動產生一個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檔案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式生命週期中各個事件的執行方法：

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

– (void)applicationWillResignActive:(UIApplication *)application;程式將要被啟用時執行，程式啟用使用者才能操作；

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

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

– (void)applicationDidBecomeActive:(UIApplication *)application;程式被啟用後執行，注意程式被啟用時會先進入前台再被啟用；

– (void)applicationWillTerminate:(UIApplication *)application;程式在終止時執行，包括正常終止或異常終止，例如說一個應用程式在背景程式佔用太多記憶體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式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。