无法在viewDidAppear之前正确设置框架

Question

我想知道是否有人知道为什么当你设置子视图的框架viewDidLoad并且viewWillAppear更改不会影响屏幕,但如果你设置viewDidAppear它们呢？

在我的情况下,我正在加载一个带有两个tableviews的自定义xib,然后尝试将它们向下移动viewDidLoad以允许添加另一个视图的空间,viewDidLoad因为它并不总是需要显示它.

问题是当我设置框架viewDidLoad或viewWillAppear在对象上设置框架时,我可以看到它打印出来,但它没有反映在屏幕上.移动我的设置框架调用viewDidAppear将导致一切按预期工作.

认为我应该能够设置框架是错误的viewDidLoad吗？

- (id)init {
    if ( self = [super initWithNibName:@"MyView" bundle:nil] ) {}

    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.descriptionWebView = [[[UIWebView alloc] initWithFrame:CGRectMake( 0, 0, self.view.frame.size.width, 200 )] autorelease];

    [self.view addSubview:self.descriptionWebView];

    self.tableView1.autoresizingMask = UIViewAutoresizingNone;
    self.tableView2.autoresizingMask = UIViewAutoresizingNone;

    [self.descriptionWebView loadRequest:[NSURLRequest requestWithURL:[[NSBundle mainBundle] URLForResource:@"...." withExtension:@"html"]]];

    table1LocationWithHeader = CGRectMake( self.tableView1.frame.origin.x, 200, self.tableView1.frame.size.width, self.tableView1.frame.size.height - 200 );
    table2LocationWithHeader = CGRectMake( self.tableView2.frame.origin.x, 200, self.tableView2.frame.size.width, self.tableView2.frame.size.height - 200 );

    //this will NOT work
    self.tableView1.frame = table1LocationWithHeader;
    self.tableView2.frame = table2LocationWithHeader;
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    //this will NOT work
    self.tableView1.frame = table1LocationWithHeader;
    self.tableView2.frame = table2LocationWithHeader;
}


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

    //this WILL work
    self.tableView1.frame = table1LocationWithHeader;
    self.tableView2.frame = table2LocationWithHeader;
}


//I added these after comments for stack overflow users, it seems like viewDidLayoutSubviews is the best place to set the frame

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];

    //this will NOT work
    self.tableView1.frame = table1LocationWithHeader;
    self.tableView2.frame = table2LocationWithHeader;
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    //this WILL work
    self.tableView1.frame = table1LocationWithHeader;
    self.tableView2.frame = table2LocationWithHeader;
}

Answer 1

在加载类时调用viewDidLoad但是没有初始化ui元素,因此在viewDidLoad和viewDidAppear调用之间的初始化过程中,任何引用它们的尝试都将被覆盖或不可用.一旦所有ui元素都被初始化并且调用了viewDidAppear.

viewDidLoad - 在控制器视图加载到内存后调用

此时视图不在视图层次结构中.

viewWillAppear - 通知视图控制器其视图即将添加到视图层次结构中.

同样,视图尚未添加到视图层次结构中.

viewDidAppear - 通知视图控制器其视图已添加到视图层次结构中.

只有这样才能将视图添加到视图层次结构中.

更新

该viewDidLayoutSubviews是最合适的地方来修改UI实际上出现在屏幕上了.

viewDidLayoutSubviews - 通知视图控制器其视图刚刚布置了其子视图.