iOS UIKit ：UIWindow

uiqwindow定义了一个window对象来管理views。一个软件只能有一个window。window的主要职能使为view提供显示取和向view传递事件。想要改变软件显示的内容，你可以改变window的root view。

 

uiwindow的screen属性指定了window的显示属性包括：bounds, mode, and brightness.

window notifications用来监听window 和 screen的改变，包括：

uiwindowdidbecomevisiblenotification
uiwindowdidbecomehiddennotification
uiwindowdidbecomekeynotification
uiwindowdidresignkeynotification uiwindow继承自uiview，关于这一点可能有点逻辑障碍，画框怎么继承自画布呢？不要过于去专牛角尖，画框的形状不就是跟画布一样吗？拿一块画布然后用一些方法把它加强，是不是可以当一个画框用呢？这也是为什么 一个view可以直接加到另一个view上去的原因了。一个应用程序只能有一个画框。

看一下的初始化过程（在application didfinishlauchingwithoptions里面）：

 

- (bool)application:(uiapplication *)application willfinishlaunchingwithoptions:(nsdictionary *)launchoptions {
   uiwindow *window = [[uiwindow alloc] initwithframe:[[uiscreen mainscreen] bounds]];
   myviewcontroller = [[myviewcontroller alloc] init];
   window.rootviewcontroller = myviewcontroller;
   [window makekeyandvisible];
   return yes;
}

 

创建一个an external display：

- (void)checkforexistingscreenandinitializeifpresent
{
    if ([[uiscreen screens] count] > 1)
    {
        // get the screen object that represents the external display.
        uiscreen *secondscreen = [[uiscreen screens] objectatindex:1];
        // get the screen's bounds so that you can create a window of the correct size.
        cgrect screenbounds = secondscreen.bounds;
 
        self.secondwindow = [[uiwindow alloc] initwithframe:screenbounds];
        self.secondwindow.screen = secondscreen;
 
        // set up initial content to display...
        // show the window.
        self.secondwindow.hidden = no;
    }
}

- (void)setupscreenconnectionnotificationhandlers
{
    nsnotificationcenter *center = [nsnotificationcenter defaultcenter];
 
    [center addobserver:self selector:@selector(handlescreendidconnectnotification:)
            name:uiscreendidconnectnotification object:nil];
    [center addobserver:self selector:@selector(handlescreendiddisconnectnotification:)
            name:uiscreendiddisconnectnotification object:nil];
}

- (void)handlescreendidconnectnotification:(nsnotification*)anotification
{
    uiscreen *newscreen = [anotification object];
    cgrect screenbounds = newscreen.bounds;
 
    if (!self.secondwindow)
    {
        self.secondwindow = [[uiwindow alloc] initwithframe:screenbounds];
        self.secondwindow.screen = newscreen;
 
        // set the initial ui for the window.
    }
}
 
- (void)handlescreendiddisconnectnotification:(nsnotification*)anotification
{
    if (self.secondwindow)
    {
        // hide and then delete the window.
        self.secondwindow.hidden = yes;
        self.secondwindow = nil;
 
    }
 
}