关于self.view.window与viewDidLoad、viewWillAppear、viewDidAppear

关于self.view.window与viewDidLoad、viewWillAppear、viewDidAppear

在进入一个界面（UIViewController），如果要在进入的时候使用self.view.window，那么必须在将使用代码放在viewDidAppear方法中，而viewDidLoad、viewWillAppear中self.view.window.frame为0{{0,0},{0,0}}。

- (void)viewDidLoad {
    NSLog(@"viewDidLoad");
    [super viewDidLoad];
}


-(void)viewWillAppear:(BOOL)animated{
    NSLog(@"viewWillAppear");
    [super viewWillAppear:animated];
}

-(void)viewDidAppear:(BOOL)animated{
    NSLog(@"viewDidAppear");
    [super viewDidAppear:animated];
    [self _doTest01];
}

- (void)_doTest01 {
    NSLog(@"_doTest01");
    //UIView
    UIView* vwFullScreenView = [[UIView alloc]init];
    vwFullScreenView.backgroundColor=[UIColor yellowColor];
    vwFullScreenView.frame=self.view.window.frame;
    NSLog(@"%@",NSStringFromCGRect(vwFullScreenView.frame));
    [self.view.window addSubview:vwFullScreenView];
    
    //UILabel
    UILabel* lblTitle = [[UILabel alloc]init];
    lblTitle.text=@"显示了@_@";
    lblTitle.frame=CGRectMake(0, 0, 200, 40);
    lblTitle.textAlignment=NSTextAlignmentCenter;
    lblTitle.backgroundColor=[UIColor whiteColor];
    lblTitle.center=vwFullScreenView.center;
    [vwFullScreenView addSubview:lblTitle];
    
}

输出：

2015-11-01 09:21:27.031 demo010[7638:261914] viewDidLoad
2015-11-01 09:21:27.032 demo010[7638:261914] viewWillAppear
2015-11-01 09:21:27.038 demo010[7638:261914] viewDidAppear
2015-11-01 09:21:27.038 demo010[7638:261914] _doTest01
2015-11-01 09:21:27.039 demo010[7638:261914] {{0, 0}, {320, 568}}

如果将[self _doTest01];代码放到viewDidLoad 或 viewWillAppear 方法中，那么输出结果如下：

2015-11-01 09:35:00.054 demo010[7762:271018] viewDidLoad
2015-11-01 09:35:00.054 demo010[7762:271018] viewWillAppear
2015-11-01 09:35:00.054 demo010[7762:271018] _doTest01
2015-11-01 09:35:00.054 demo010[7762:271018] {{0, 0}, {0, 0}}
2015-11-01 09:35:00.061 demo010[7762:271018] viewDidAppear

可以看到self.view.window的frame为 {{0, 0}, {0, 0}}，说明此时self.view.window还没显示出来。