UIWindow并不包含任何默認(rèn)的內(nèi)容，但是它被當(dāng)作UIView的容器，用于放置應(yīng)用中所有的UIView。UIWindow更多的時(shí)候只作為UIView的頂層容器存在。
而我們最常用的方法，就是在程序剛啟動(dòng)時(shí)，調(diào)用UIWindow的makeAndVisible方法，代碼如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    ViewController *vc = [[ViewController alloc] init];
    UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:vc];
    self.window.rootViewController = nav;
    [self.window makeKeyAndVisible];
    return YES;
}```
我們可以在UIWindow做一些操作：

// 取得最上面的window self代表一個(gè)view
UIWindow *window = [[UIApplication sharedApplication].windows lastObject];
[window addSubview:self];

WindowLevel屬性
不是所有創(chuàng)建的UIWindow一定會(huì)覆蓋在界面的最上面，UIWindow有一個(gè)類型為“UIWindowLevel”的屬性，該屬性定義了UIWindow的層級(jí)，系統(tǒng)定義的UIWindowLevel一共有3中取值：如下：

UIKIT_EXTERN const UIWindowLevel UIWindowLevelNormal;
UIKIT_EXTERN const UIWindowLevel UIWindowLevelAlert;
UIKIT_EXTERN const UIWindowLevel UIWindowLevelStatusBar

程序中默認(rèn)的UIWindow的層級(jí)是UIWindowLevelNormal。

手動(dòng)創(chuàng)建UIWindow

//創(chuàng)建UIWindown
_window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
_window.windowLevel = UIWindowLevelNormal;
_window.backgroundColor = [UIColor blueColor];
_window.hidden = NO;

UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(hideUIWindown)];
[_window addGestureRecognizer:tap];

/**
隱藏UIWindown
*/

• (void)hideUIWindown{
  _window.hidden = YES;
  _window = nil;
  }

在一個(gè)應(yīng)用程序中，想做一個(gè)密碼保護(hù)功能，在用戶從應(yīng)用的任何界面按Home鍵退出，過(guò)一段時(shí)間再?gòu)暮笈_(tái)切換回來(lái)，顯示一個(gè)密碼輸入界面。只有用戶在輸入正確的密碼，才能夠進(jìn)入退出的界面。因?yàn)檫@個(gè)密碼輸入界面可能從任何應(yīng)用界面彈出，并且需要蓋在所有界面的最上層，所以它很適合用一個(gè)UIWindow來(lái)實(shí)現(xiàn)。

import "PasswordInputwindow.h"

@implementation PasswordInputwindow

• (instancetype)shareInstance
  {
  static id shareInstance = nil;
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
  shareInstance = [[self alloc] initWithFrame:[UIScreen mainScreen].bounds];
  });
  return shareInstance;
  }

• (instancetype)initWithFrame:(CGRect)frame
  {
  self = [super initWithFrame:frame];
  if (self) {
  UIViewController *vc = [[UIViewController alloc] init];
  vc.view.backgroundColor = [UIColor yellowColor];
  self.rootViewController = vc;

    UITextField *textfield = [[UITextField alloc] init];
    textfield.textColor = [UIColor blackColor];
    textfield.font = [UIFont systemFontOfSize:17];
    textfield.frame = CGRectMake(20, 120, [UIScreen mainScreen].bounds.size.width-40, 40);
    textfield.borderStyle = UITextBorderStyleRoundedRect;
    textfield.placeholder = @"在這里輸入密碼";
    [vc.view addSubview:textfield];
    
    UIButton *btn = [[UIButton alloc] init];
    [btn setTitle:@"隱藏界面" forState:UIControlStateNormal];
    [btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
    btn.titleLabel.font = [UIFont systemFontOfSize:17];
    [btn sizeToFit];
    btn.center = CGPointMake([UIScreen mainScreen].bounds.size.width/2, [UIScreen mainScreen].bounds.size.height/2);
    [btn addTarget:self action:@selector(hideWindown:) forControlEvents:UIControlEventTouchUpInside];
    [vc.view addSubview:btn];
  

  }

  return self;
  }

• (void)hideWindown:(UIButton *)sender{
  [self resignKeyWindow];
  self.hidden = YES;
  }

• (void)show
  {
  [self makeKeyWindow];
  self.hidden = NO;
  }

• (void)applicationDidBecomeActive:(UIApplication *)application {

  [[PasswordInputwindow shareInstance] show];
  }

如果我們創(chuàng)建的UIWindow需要處理鍵盤事件，那么就需要合理的將其設(shè)置為keywindow。keywindow是被系統(tǒng)設(shè)計(jì)用來(lái)接受鍵盤和其他非觸摸事件的UIWindow。我們可以通過(guò)makeKeyWindow和makeKeyAndVisible方法來(lái)將自己創(chuàng)建的UIWindow實(shí)例設(shè)置為keywindow。支付寶客戶端的手勢(shì)解鎖功能，就是UIWindow的一個(gè)極好的應(yīng)用。


/***  文中的知識(shí)摘自“iOS開發(fā)進(jìn)階”   ****/