精通IOS開發-GCD和幕後處理

標籤：

一些生命週期函數的調用時間

開啟應用時，調用

applicationWillEnterForeground:

applicationDidBecomeActive:

 

按Home鍵，調用

applicationWillResignActive:

applicationDidEnterBackground:

 

雙擊Home鍵，向上滑動關閉程式，調用

applicationWillTerminate:

 

狀態儲存和回複機制參考

http://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/Strategiesfor-ImplementingYourApp/StrategiesforImplementingYourApp.html 的App Programming Guide for iOS

 

// 在AppDelegate.m中每一個方法添加以下語句，用於運行程式切換狀態時，觀察相關方法的調用NSLog(@"%@",NSStringFromSelector(_cmd));

////  ViewController.m//  State Lab////  Created by  Jierism on 16/7/31.//  Copyright © 2016年  Jierism. All rights reserved.//#import "ViewController.h"@interface ViewController ()@property (strong,nonatomic) UILabel *label;@property (strong,nonatomic) UIImage *smiley;@property (strong,nonatomic) UIImageView *smileyView;@property (assign,nonatomic) NSInteger index;@property (strong,nonatomic) UISegmentedControl *segmentedControl;@end@implementation ViewController{    BOOL animate;}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.        // 設定Label    CGRect bounds = self.view.bounds;    CGRect labelFrame = CGRectMake(bounds.origin.x, CGRectGetMidY(bounds)-50, bounds.size.width, 100);    self.label = [[UILabel alloc] initWithFrame:labelFrame];    self.label.font = [UIFont fontWithName:@"Helvetica" size:70];    self.label.text = @"Bazinga!";    self.label.textAlignment = NSTextAlignmentCenter;    self.label.backgroundColor = [UIColor clearColor];    [self.view addSubview:self.label];        // 設定smiley映像,尺寸是84像素X84像素    CGRect smileyFrame = CGRectMake(CGRectGetMidX(bounds)-42, CGRectGetMidY(bounds)/2-42, 84, 84);    self.smileyView = [[UIImageView alloc] initWithFrame:smileyFrame];    self.smileyView.contentMode = UIViewContentModeCenter;    NSString *smileyPath = [[NSBundle mainBundle] pathForResource:@"smiley" ofType:@"png"];    self.smiley = [UIImage imageWithContentsOfFile:smileyPath];    self.smileyView.image = self.smiley;    [self.view addSubview:self.smileyView];        // 建立分段控制項    self.segmentedControl = [[UISegmentedControl alloc] initWithItems:[NSArray arrayWithObjects:@"One",@"Two",@"Three",@"Four",nil]];    self.segmentedControl.frame = CGRectMake(bounds.origin.x+20, 50, bounds.size.width-40, 30);    [self.segmentedControl addTarget:self                              action:@selector(selectionChanged:)                    forControlEvents:UIControlEventValueChanged];    [self.view addSubview:self.segmentedControl];        // 從後台返回時顯示原來的分段控制項index值的狀態,並設定預設選中第一個    self.index = [[NSUserDefaults standardUserDefaults] integerForKey:@"index"];    self.segmentedControl.selectedSegmentIndex = self.index;        // 改變應用程式狀態會通知應用程式委託，不過因為我們的類不是應用委託，所以無法實現委託方法並期望他們生效，    // 但我們可以註冊以接受在執行裝填更改是來自應用的通知    // 當程式在運行過程中受到簡訊時，通過改變animate標記，會停止轉動，關閉簡訊視窗後會繼續轉動    NSNotificationCenter *center = [NSNotificationCenter defaultCenter];    [center addObserver:self               selector:@selector(applicationWillResignActive)                   name:(UIApplicationWillResignActiveNotification)                 object:nil];    [center addObserver:self               selector:@selector(applicationDidBecomeActive)                   name:UIApplicationDidBecomeActiveNotification                 object:nil];        // 再註冊兩個通知，用以下兩個方法實現，當程式進入後台時回收笑臉的資源，當程式從後台返回時重新建立它，最佳化系統資源    [center addObserver:self               selector:@selector(applicationDidEnterBackground)                   name:(UIApplicationWillResignActiveNotification)                 object:nil];    [center addObserver:self               selector:@selector(applicationWillEnterForeground)                   name:UIApplicationDidBecomeActiveNotification                 object:nil];}- (void)rotateLabelDown{    [UIView animateWithDuration:0.5 animations:^{        self.label.transform = CGAffineTransformMakeRotation(M_PI);    }     completion:^(BOOL finished) {         [self rotateLabelUp];     }];}- (void)rotateLabelUp{    [UIView animateWithDuration:0.5 animations:^{        self.label.transform = CGAffineTransformMakeRotation(0);    }                     completion:^(BOOL finished) {                                                  if (animate) {                             [self rotateLabelDown];                         }                                              }];}// 程式將要變為不活躍- (void)applicationWillResignActive{    NSLog(@"VC:%@",NSStringFromSelector(_cmd));    animate = NO;}// 程式變為活躍- (void)applicationDidBecomeActive{    NSLog(@"VC:%@",NSStringFromSelector(_cmd));    animate = YES;    [self rotateLabelDown];}// 程式進入後台，釋放圖片- (void)applicationDidEnterBackground{    NSLog(@"VC:%@",NSStringFromSelector(_cmd));    self.smiley = nil;    self.smileyView = nil;    [[NSUserDefaults standardUserDefaults] setInteger:self.index forKey:@"index"];        // 請求更多的後台時間，當程式進如後台時，向系統請求時間繼續執行任務    UIApplication *app = [UIApplication sharedApplication];    // 調用beginBackgroundTaskWithExpirationHandler和endBackgroundTask匹配調用，是在告訴系統：我們需要更多時間來完成某件事，並承諾在完成後告訴他。如果系統斷定我們運行了太長的時間並決定停止背景工作，可以調用我們作為參數提供的代碼塊。    __block UIBackgroundTaskIdentifier taskId = [app beginBackgroundTaskWithExpirationHandler:^{        NSLog(@"Background task ran out of time and was terminated.");        [app endBackgroundTask:taskId];    }];        // 如果返回特殊值UIBackgroundTaskInvalid，則表明系統沒有為我們提供任何多餘的時間    if (taskId == UIBackgroundTaskInvalid) {        NSLog(@"Failed to start background task!");        return;    }        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{        NSLog(@"Starting background task with %f seconds remaining",app.backgroundTimeRemaining);        self.smiley = nil;        self.smileyView = nil;        // 類比一個25s的過程        [NSThread sleepForTimeInterval:25];                NSLog(@"Finishing background task with %f seconds remaining",app.backgroundTimeRemaining);        // 告訴系統我們完成了之前請求額外時間來完成的工作        [app endBackgroundTask:taskId];    });}// 程式從後台返回時載入圖片- (void)applicationWillEnterForeground{    NSLog(@"VC:%@",NSStringFromSelector(_cmd));    NSString *smileyPath = [[NSBundle mainBundle] pathForResource:@"smiley" ofType:@"png"];    self.smiley = [UIImage imageWithContentsOfFile:smileyPath];    self.smileyView.image = self.smiley;}// 每當使用者改變了所選的分段，index屬性的值就會更新- (void)selectionChanged:(UISegmentedControl *)sender{    self.index = sender.selectedSegmentIndex;}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end

 

精通IOS開發-GCD和幕後處理