标签：ios开发   uiwindow   

关于UIWindowLevel
定义了UIWindow的层级，系统有3个取值

UIKIT_EXTERN const UIWindowLevel UIWindowLevelNormal; UIKIT_EXTERN const UIWindowLevel UIWindowLevelAlert; UIKIT_EXTERN const UIWindowLevel UIWindowLevelStatusBar; NSLog(@"UIWindowLevelNormal:%f,UIWindowLevelAlert:%f,UIWindowLevelStatusBar:%f",UIWindowLevelNormal,UIWindowLevelAlert,UIWindowLevelStatusBar);

output:

UIWindowLevelNormal:0.000000,UIWindowLevelAlert:2000.000000,UIWindowLevelStatusBar:1000.000000;

系统默认层级是UIWindowLevelNormal，如果有UIAlertView，会创建层级为UIWindowLevelAlert的UIWindow，其UIWindowLevel值更高，覆盖在上面，实际应用中，UIWindowLevel值不止这3个；

手动创建UIWindow，区别于UIView，UIWindow一旦被创建，将自动地添加到整个界面上~

手动创建UIWindow

#import "ViewController.h" @interface ViewController () { UIWindow *_myWindow; } @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; self.view.backgroundColor = [UIColor redColor]; //创建Button，点击创建UIWindow UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 50)]; [button setTitle:@"创建window" forState:UIControlStateNormal]; [button addTarget:self action:@selector(_creatAction:) forControlEvents:UIControlEventTouchUpInside]; button.center = self.view.center; [self.view addSubview:button]; // Do any additional setup after loading the view, typically from a nib. } - (void)_creatAction:(UIButton *)btn { //创建一个UIWindow _myWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds]; _myWindow.windowLevel = UIWindowLevelNormal; _myWindow.backgroundColor = [UIColor blackColor]; _myWindow.alpha = 0.7; _myWindow.hidden = NO; //添加手势 UIGestureRecognizer *gesture = [[UITapGestureRecognizer alloc] init]; [gesture addTarget:self action:@selector(hideWindow:)]; [_myWindow addGestureRecognizer:gesture]; // 在window上添加一个UILabel UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 200, 20)]; label.text = @"LABEL"; [label setTextColor:[UIColor whiteColor]]; [_myWindow addSubview:label]; } - (void)hideWindow:(UIGestureRecognizer *)gesture { _myWindow.hidden = YES; _myWindow = nil; }

注意：
1、UIWindow不可滥用理应由ViewController实现的效果，就应该用ViewController addSubview来实现；
2、不可将需要弹出的界面都设置为单例，需要时调用显示，这会使得新创建的UIWindow一直得不到释放，出现多个UIWindow需要下过户有层级覆盖关系式，，实现起来会比较复杂
（单例模式的意思就是只有一个实例。单例模式确保某一个类只有一个实例，而且自行实例化并向整个系统提供这个实例。这个类称为单例类。）

以上为阅读《iOS开发进阶》第十二章摘记及练习