AutoLayout 以编程方式不起作用

Question

我想深入了解自动布局，所以我想以编程方式进行，以便理解它 properly.I 知道如何通过故事板漂亮地使用它 well.Now 这就是我正在做（在 viewDidAppear:）

-(void)scenario2{

    PGView *viewA = [[PGView alloc]initWithFrame:CGRectMake(100, 100, 100, 100) andBackgroundColor:[UIColor blackColor]];
    [self.view addSubview:viewA];

    PGView *viewB = [[PGView alloc]initWithFrame:CGRectMake(200, 300, 100, 100) andBackgroundColor:[UIColor yellowColor]];
    [self.view addSubview:viewB];

    viewA.translatesAutoresizingMaskIntoConstraints = NO;
    viewB.translatesAutoresizingMaskIntoConstraints = NO;

    NSLayoutConstraint *constraint;

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[viewB(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewB)]];

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[viewB(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewB)]];

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[viewA(==200)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewA)]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[viewA(==200)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewA)]];

    //problem statement
    constraint = [NSLayoutConstraint constraintWithItem:viewA attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:viewB attribute:NSLayoutAttributeWidth multiplier: 3.0f constant: 0.0f];
    [self.view addConstraint:constraint];

    NSLog(@"%@",viewA);
    NSLog(@"%@",viewB);

}

所以这里我初始化了两个不同颜色的view
我知道我需要设置属性。 translatesAutoresizingMaskIntoConstraints 到 NO，然后再应用任何新约束。所以我做到了。
现在我指定 views.So 的高度和宽度，两个视图的 x_position 和 y_position 都是 0.I 运行代码，我得到了预期的结果。两个视图在 (0,0) 点都有指定的高度和宽度。

问题

现在当我写语句"problem statement"根据viewA的宽度调整viewB的宽度时，它不起作用。
此外，当我打印视图 viewA 和 viewB 时，它会将帧打印为 (0,0,0,0)。

谁能给我解释一下这种行为？

编辑：这是我所做的一些修改 made.I 使用 'hasAmbiguousLayout' 检查了两个视图的歧义及其工作正常 now.Now 如果我下一步应该做什么想要将 viewB 的宽度调整为 viewA 的宽度的三倍？

-(void)scenario2{

PGView *viewA = [PGView new];
viewA.backgroundColor = [UIColor yellowColor];
[self.view addSubview:viewA];

PGView *viewB = [PGView new];
viewB.backgroundColor = [UIColor blackColor];
[self.view addSubview:viewB];

viewA.translatesAutoresizingMaskIntoConstraints = NO;
viewB.translatesAutoresizingMaskIntoConstraints = NO;

NSLayoutConstraint *constraint;

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[viewB(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewB)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[viewB(==100)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewB)]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[viewA(==200)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewA)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[viewA(==200)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(viewA)]];


NSLog(@"%d",viewA.hasAmbiguousLayout);
NSLog(@"%d",viewB.hasAmbiguousLayout);

NSLog(@"%@",viewA);
NSLog(@"%@",viewB);

}

Answer 1

问题是您已经明确地将 A 和 B 的宽度限制分别设置为 200 和 100。因此，当与其他约束结合使用时，指定一个宽度应为另一个宽度的三倍的附加约束无法满足。

此外，约束是不明确的，因为您已经定义了宽度和高度约束，但还没有定义这两个框架应该在哪里。是的，您已经为这两个视图定义了 frame，但是当您应用约束时它会被忽略。您可能根本不应该定义 frame 值，因为它具有误导性和混淆性。但是你应该设置，例如，leading 和 top 约束，或者在 VFL 中指定它们，或者添加 centerX 和 centerY 约束。您只需要一些约束来指定视图的放置位置，并且有很多方法可以指定它。

最后您没有看到合理的 frame 值的原因是您已经定义了约束，但尚未应用它们。如果需要，您可以在 viewDidLayoutSubviews 中检查它们。

您可以这样做：

- (void)scenario2 {

    PGView *viewA = [PGView new];
    viewA.backgroundColor = [UIColor yellowColor];
    [self.view addSubview:viewA];

    PGView *viewB = [PGView new];
    viewB.backgroundColor = [UIColor blackColor];
    [self.view addSubview:viewB];

    viewA.translatesAutoresizingMaskIntoConstraints = NO;
    viewB.translatesAutoresizingMaskIntoConstraints = NO;

    NSDictionary *views = NSDictionaryOfVariableBindings(viewA, viewB);

    // note, I added `|-100-` to say it's 100 points from the top (and 100 tall)

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[viewB(==100)]" options:0 metrics:nil views:views]];

    // likewise, to say 200 points from the left (and 100 wide)

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-200-[viewB(==100)]" options:0 metrics:nil views:views]];

    // again, 100 from the top (as well as 200 tall)

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-100-[viewA(==200)]" options:0 metrics:nil views:views]];

    // and 100 from the left
    // but I've removed width definition, as we'll use your multiplier constraint below

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-100-[viewA]" options:0 metrics:nil views:views]];

    // now that we've removed the width constraint from the above,
    // this should now work fine

    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:viewA attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:viewB attribute:NSLayoutAttributeWidth multiplier: 3.0f constant: 0.0f];
    [self.view addConstraint:constraint];

    // no point in doing this, because constraints haven't yet been applied
    //
    // NSLog(@"%@",viewA);
    // NSLog(@"%@",viewB);
}

// if you want to see where they are, you could do that here:

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];

    for (UIView *view in self.view.subviews) {
        NSLog(@"%@", view);
    }
    NSLog(@"-----");
}

AutoLayout 以编程方式不起作用

AutoLayout programmatically doesn't work

ios

autolayout

programmatically-created