关于UIWindow的一点儿思考

UIWindow的一点儿思考

  每一个IOS程序都有一个UIWindow,在我们通过模板简历工程的时候,xcode会自动帮我们生成一个window,然后让它变成keyWindow并显示出来。这一切都来的那么自然,以至于我们大部分时候都忽略了自己也是可以创建UIWindow对象。

  通常在我们需要自定义UIAlertView的时候(IOS 5.0以前AlertView的背景样式等都不能换)我们可以使用UIWindow来实现(设置windowLevel为Alert级别),网上有很多例子,这里就不详细说了。

  我的上一篇文章UIWindowLevel详解,中讲到了关于Windowlevel的东西,当时还只是看了看文档,知道有这么一回儿事。今天刚好遇到这块儿的问题,就顺便仔细看了一下UIWindow方面的东西,主要包括:WindowLevel以及keyWindow两个方面。

一、UIWindowLevel

  我们都知道UIWindow有三个层级,分别是Normal,StatusBar,Alert。打印输出他们三个这三个层级的值我们发现从左到右依次是0,1000,2000,也就是说Normal级别是最低的,StatusBar处于中等水平,Alert级别最高。而通常我们的程序的界面都是处于Normal这个级别上的,系统顶部的状态栏应该是处于StatusBar级别,UIActionSheet和UIAlertView这些通常都是用来中断正常流程,提醒用户等操作,因此位于Alert级别。

  上一篇文章中我也提到了一个猜想,既然三个级别的值之间相差1000,而且我们细心的话查看UIWindow的头文件就会发现有一个实例变量_windowSublevel,那我们就可以定义很多中间级别的Window。例如可以自定义比系统UIAlertView级别低一点儿的window。于是写了一个小demo,通过打印发现系统的UIAlertView的级别是1996,而与此同时UIActionSheet的级别是2001,这样也验证了subLevel的确存在。

    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Alert View"
                                                        message:@"Hello Wolrd, i'm AlertView!!!"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:@"Cancel", nil];
    [alertView show];
    [alertView release];
    
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:@"ActionSheet"
                                                             delegate:nil
                                                    cancelButtonTitle:@"Cancel"
                                               destructiveButtonTitle:@"Don't do that!"
                                                    otherButtonTitles:@"Hello Wolrd", nil];
    [actionSheet showInView:self.view];
    [actionSheet release];

  下面是程序运行截图:

  根据window显示级别优先的原则,级别高的会显示在上面,级别低的在下面,我们程序正常显示的view位于最底层,至于具体怎样获取UIAlertView和UIActionSheet的level,我会在下面第二部分keyWindow中介绍并给出相应的代码。

二、KeyWindow

  什么是keyWindow,官方文档中是这样解释的"The key window is the one that is designated to receive keyboard and other non-touch related events. Only one window at a time may be the key window." 翻译过来就是说,keyWindow是指定的用来接收键盘以及非触摸类的消息,而且程序中每一个时刻只能有一个window是keyWindow。

  下面我们写个简单的例子看看非keyWindow能不能接受键盘消息和触摸消息,程序中我们在view中添加一个UITextField,然后新建一个alert级别的window,然后通过makeKeyAndVisible让它变成keyWindow并显示出来。代码如下:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
    // Override point for customization after application launch.
    self.viewController = [[[SvUIWindowViewController alloc] initWithNibName:@"SvUIWindowViewController" bundle:nil] autorelease];
    self.window.rootViewController = self.viewController;
    [self.window makeKeyAndVisible];
    
    UIWindow *window1 = [[UIWindow alloc] initWithFrame:CGRectMake(0, 80, 320, 320)];
    window1.backgroundColor = [UIColor redColor];
    window1.windowLevel = UIWindowLevelAlert;
    [window1 makeKeyAndVisible];

    return YES;
}
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self registerObserver];
    
    // add a textfield
    UITextField *filed = [[UITextField alloc] initWithFrame:CGRectMake(0, 0, 320, 60)];
    filed.placeholder = @"Input something here";
    filed.clearsOnBeginEditing = YES;
    filed.borderStyle = UITextBorderStyleRoundedRect;
    [self.view addSubview:filed];
    [filed release];
}

  运行截图如下:

  从图中可以看出,虽然我们自己新建了一个然后设置为keyWindow并显示,但是点击程序中默认window上添加的textField还是可以唤出键盘,而且还可以正常接受键盘输入,只是键盘被挡住了,说明非keyWindow也是可以接受键盘消息,这一点和文档上说的不太一样。

  观察UIWindow的文档,我们可以发现里面有四个关于window变化的通知:

  UIWindowDidBecomeVisibleNotification

  UIWindowDidBecomeHiddenNotification

  UIWindowDidBecomeKeyNotification

  UIWindowDidResignKeyNotification

  这四个通知对象中的object都代表当前已显示(隐藏),已变成keyWindow(非keyWindow)的window对象,其中的userInfo则是空的。于是我们可以注册这个四个消息,再打印信息来观察keyWindow的变化以及window的显示,隐藏的变动。

  代码如下:

SvUIWindowViewController.m
//
//  SvUIWindowViewController.m
//  SvUIWindowSample
//
//  Created by  maple on 11/14/12.
//  Copyright (c) 2012 maple. All rights reserved.
//

#import "SvUIWindowViewController.h"
#import "SvCustomWindow.h"

@interface SvUIWindowViewController ()

- (void)presentAlertView;
- (void)presentActionSheet;

// observer
- (void)registerObserver;
- (void)unregisterObserver;

// observer handler
- (void)windowBecomeKey:(NSNotification*)noti;
- (void)windowResignKey:(NSNotification*)noti;
- (void)windowBecomeVisible:(NSNotification*)noti;
- (void)windowBecomeHidden:(NSNotification*)noti;


@end

@implementation SvUIWindowViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    [self registerObserver];
    
    // add a textfield
    UITextField *filed = [[UITextField alloc] initWithFrame:CGRectMake(0, 0, 320, 60)];
    filed.placeholder = @"Input something here";
    filed.clearsOnBeginEditing = YES;
    filed.borderStyle = UITextBorderStyleRoundedRect;
    [self.view addSubview:filed];
    [filed release];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
    
    [self unregisterObserver];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    
//    [self presentAlertView];

//    [self presentActionSheet];
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

#pragma mark -
#pragma mark observer

- (void)registerObserver
{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(windowBecomeKey:) name:UIWindowDidBecomeKeyNotification object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(windowResignKey:) name:UIWindowDidResignKeyNotification object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(windowBecomeVisible:) name:UIWindowDidBecomeVisibleNotification object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(windowBecomeHidden:) name:UIWindowDidBecomeHiddenNotification object:nil];
}

- (void)unregisterObserver
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}


#pragma mark -
#pragma mark Test AlertView & ActionSheet

- (void)presentAlertView
{
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Alert View"
                                                        message:@"Hello Wolrd, i'm AlertView!!!"
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:@"Cancel", nil];
    [alertView show];
    [alertView release];
}

- (void)presentActionSheet
{
    UIActionSheet *actionSheet = [[UIActionSheet alloc] initWithTitle:@"ActionSheet"
                                                             delegate:nil
                                                    cancelButtonTitle:@"Cancel"
                                               destructiveButtonTitle:@"Don't do that!"
                                                    otherButtonTitles:@"Hello Wolrd", nil];
    [actionSheet showInView:self.view];
    [actionSheet release];
}

#pragma mark -
#pragma mark Notification handler

- (void)windowBecomeKey:(NSNotification*)noti
{
    UIWindow *window = noti.object;
    NSArray *windows = [UIApplication sharedApplication].windows;
    NSLog(@"current window count %d", windows.count);
    NSLog(@"Window has become keyWindow: %@, window level: %f, index of windows: %d", window, window.windowLevel, [windows indexOfObject:window]);
}

- (void)windowResignKey:(NSNotification*)noti
{
    UIWindow *window = noti.object;
    NSArray *windows = [UIApplication sharedApplication].windows;
    NSLog(@"current window count %d", windows.count);
    NSLog(@"Window has Resign keyWindow: %@, window level: %f, index of windows: %d", window, window.windowLevel, [windows indexOfObject:window]);
}

- (void)windowBecomeVisible:(NSNotification*)noti
{
    UIWindow *window = noti.object;
    NSArray *windows = [UIApplication sharedApplication].windows;
    NSLog(@"current window count %d", windows.count);
    NSLog(@"Window has become visible: %@, window level: %f, index of windows: %d", window, window.windowLevel, [windows indexOfObject:window]);
}

- (void)windowBecomeHidden:(NSNotification*)noti
{
    UIWindow *window = noti.object;
    NSArray *windows = [UIApplication sharedApplication].windows;
    NSLog(@"current window count %d", windows.count);
    NSLog(@"Window has become hidden: %@, window level: %f, index of windows: %d", window, window.windowLevel, [windows indexOfObject:window]);
}

@end

  a、当我们打开viewDidAppear中“[self presentAlertView];”的时候,控制台输出如下

  根据打印的信息我们可以看出流程如下:

  1、程序默认的window先显示出来

  2、默认的window再变成keyWindow

  3、AlertView的window显示出来

  4、默认的window变成非keyWindow

  5、最终AlertView的window变成keyWindow

  总体来说就是“要想当老大(keyWindow),先从小弟(非keyWindow)开始混起” 而且根据打印的信息我们同事可以知道默认的window的level是0,即normal级别;AlertView的window的level是1996,比Alert级别稍微低了一点儿。

  b、当我们打开viewDidAppear中“[self presentActionSheet];”的时候,控制台输出如下:  

  keyWindow的变化和window的显示和上面的流程一样,同时我们可以看出ActionSheet的window的level是2001。

  c、接着上一步,我们点击弹出ActionSheet的cancel的时候,控制台输出如下:

  我们看出流程如下:

  1、首先ActionSheet的window变成非keyWindow

  2、程序默认的window变成keyWindow

  3、ActionSheet的window在隐藏掉

  总体就是“想隐居幕后可以,但得先交出权利”。

 

  以上是这两天遇到的,总结一下,欢迎补充,如果有不对的地方也请多多指正。

注:本文欢迎转载,转载请注明出处。同时欢迎加我qq,期待与你一起探讨更多问题。

posted on 2012-11-16 00:00 一片-枫叶 阅读(...) 评论(...) 编辑 收藏

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