ios - 如何使约束(自动布局)以编程方式工作
<p><p>这是我的第一个 iOS 项目,因此我在约束和自动布局方面遇到了困难。</p>
<p>这就是我想要做的。我想将 subview 添加到 UIScrollView。这是我以编程方式做的,因为 subview 的数量不是静态的。当我只是添加单个 subview (在代码或 XIB 中)或通过 XIB 添加多个 subview 时,我可以使自动布局和约束完美地工作。但是我无法让它与代码中动态数量的 subview 一起工作。 </p>
<p> subview 的许多实例被创建,但它们都在彼此之上,因为约束不起作用。我希望他们在每个下面排列,这就是为什么我试图让约束起作用。 (现在我只是将 subview 的数量设置为 10,但这只是暂时的)</p>
<p>这是我的一些代码(从按下按钮开始):</p>
<pre><code>-(IBAction) buttonTapped:(id)sender {
UIScrollView *matchScrollView = (UIScrollView *) ;
NSMutableArray *matchViewsArray = [ init];
for (int i = 0; i <= 9; i++) {
MatchView *newMatchView = [ loadNibNamed:@"MatchView" owner:self options:nil].firstObject;
;
}
for (int i = 0; i < ; i++) {
MatchView *newMatchView = matchViewsArray;
//I kept some IBOutlets out of the code example here. They work fine with a single subview. or even multiple subviews as long as you don't mind they are all on top of each other due to constraints not working xD
;
];
attribute:NSLayoutAttributeLeading
relatedBy:NSLayoutRelationEqual
toItem:matchScrollView
attribute:NSLayoutAttributeLeading
multiplier:1.0
constant:8.0]];
attribute:NSLayoutAttributeTrailing
relatedBy:NSLayoutRelationEqual
toItem:matchScrollView
attribute:NSLayoutAttributeTrailing
multiplier:1.0
constant:8.0]];
//If this is not the first object, then the top of the object contraints with the bottom of the previous object
if (i > 0) {
// I think the fault may lie here. Do i need to remove the previous constraint, or will it be overwritten? This did not work however, did i remove it wrong?
//Making sure it only tries to call removeconstraint: once and once only, as the constraint is only put on the else statement which only executes on the very first object. Attempt to fix the code
if (i == 1) {
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:matchScrollView
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:8.0]];
}
addConstraint:
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:matchViewsArray
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:8.0]];
}
//The top of the first object constraints with the top of the matchScrollView
else {
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:matchScrollView
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:8.0]];
}
//If this is the last object, then the bottom of the object constraints with the bottom of matchScrollView
if ( i == - 1) {
//tried removing the constraint created by else statement first before adding a new constraint
removeConstraint:
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:matchViewsArray
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:8.0]];
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationGreaterThanOrEqual
toItem:matchScrollView
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:8.0]];
}
//else the bottom of the object contraints with the top of the next object
else {
addConstraint:
attribute:NSLayoutAttributeBottom
relatedBy:NSLayoutRelationEqual
toItem:matchViewsArray
attribute:NSLayoutAttributeTop
multiplier:1.0
constant:8.0]];
}
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:matchScrollView
attribute:NSLayoutAttributeCenterX
multiplier:1.0
constant:0.0]];
}
</code></pre>
<p>}</p>
<p>我不断收到“以 NSException 类型的未捕获异常终止”。我尝试在添加新约束之前删除旧约束,但这没有帮助。除非我删除它们是错误的?</p>
<p>如果我删除所有 if 和 else 语句,只创建一个 subview ,那么约束就可以完美地工作。如果我创建多个 subview ,则应用程序不会崩溃,但 subview 都具有相同的约束并且彼此重叠。因此,通过添加 if 和 else 语句并使用 matchViewsArray 我尝试为多个 subview 设置约束。</p>
<p>此外,即使这段代码有效,真的没有更简单的方法来代替循环中的所有这些 if 和 else 语句吗?</p>
<p>如前所述,这是我的第一个 iOS 项目,因此可能有更有效和更好的方法来实现我想要的行为。</p>
<p>任何帮助将不胜感激。</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>很遗憾,我没有制作 iOS 应用程序的许可,也无法按原样对其进行测试,但这个 OSX 代码段可能会有所帮助:</p>
<pre><code>- (void)applicationDidFinishLaunching:(NSNotification *)notification
{
NSView *contentView = ;
NSMutableArray *buttons = [ init];
for (int i = 0; i < 10; i++) {
NSButton *button = [ initWithFrame:NSZeroRect];
;
];
;
]];
;
;
;
}
int count = (int);
// 1. one below other
// 2. all equal width
for (int i = 1; i < count; i++) {
NSView *view1 = buttons;
NSView *view2 = buttons;
NSDictionary *views = NSDictionaryOfVariableBindings(view1, view2);
-"
options:0
metrics:nil
views:views]];
"
options:0
metrics:nil
views:views]];
}
// 3. first -> top
if (count > 0) {
NSView *view = ;
NSDictionary *views = NSDictionaryOfVariableBindings(view);
"
options:0
metrics:nil
views:views]];
}
// 4. last -> bottom
if (count > 0) {
NSView *view = ;
NSDictionary *views = NSDictionaryOfVariableBindings(view);
-|"
options:0
metrics:nil
views:views]];
}
// 5. left <- all -> right
for (int i = 0; i < count; i++) {
NSView *view = buttons;
NSDictionary *views = NSDictionaryOfVariableBindings(view);
-(>=20)-|"
options:0
metrics:nil
views:views]];
}
}
</code></pre>
<p> <img src="/image/QX4Mr.png" alt="What it looks like"/> </p>
<p>请注意,如果不使用“视觉格式语言”,则无法指定默认的 8/20 间距,因为 <code>constraintsWithVisualFormat:...</code> 会产生特殊的约束(当然,内部带有特殊的私有(private)标志)会自动- 在特定情况下将 8 调整为 6/4/根据 Apple 的 HIG 调整大小。 (您可以尝试在 IB 中放置控件,然后发现默认值并不总是 8,但在运行时突然变为 8!)。</p>
<p><strong>编辑:</strong>此外,您可以始终使用简单的#define 或子例程来隐藏 [[]]梯子。</p>
<p><strong>edit2:</strong>重构阶段:)</p></p>
<p style="font-size: 20px;">关于ios - 如何使约束(自动布局)以编程方式工作,我们在Stack Overflow上找到一个类似的问题:
<a href="https://stackoverflow.com/questions/29661991/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/29661991/
</a>
</p>
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