當(dāng)使用xib或storyBoard構(gòu)建項(xiàng)目,并使用了AutoLayout之后,當(dāng)需要為視圖添加動(dòng)畫,或者手動(dòng)更改視圖的frame的時(shí)候,就需要修改約束啦.別以為代碼中修改約束很麻煩,其實(shí)還蠻簡(jiǎn)單的啦.
例如: 跟隨鍵盤彈出的ToolBar,原來在視圖底部,當(dāng)鍵盤彈出時(shí),ToolBar跟隨鍵盤彈出
<li>首先將ToolBar到底部的約束添加一個(gè)IBOutlet</li>
<pre><code>
@property (weak, nonatomic) IBOutlet NSLayoutConstraint *toolViewBottomConstraint;
</code></pre>
<li>鍵盤彈出修改約束</li>
<pre><code>
//鍵盤的通知(顯示)
-
(void)keyboardWillShow:(NSNotification )notification
{
NSValue aValue = [[notification userInfo] objectForKey:UIKeyboardFrameEndUserInfoKey];
CGRect keyboardRect = [aValue CGRectValue];
NSNumber *durationValue = [notification userInfo][UIKeyboardAnimationDurationUserInfoKey];
NSTimeInterval animationDuration = durationValue.doubleValue;[UIView animateWithDuration:animationDuration delay:0.0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
_toolViewBottomConstraint.constant = keyboardRect.size.height;//修改距離底部的約束
} completion:^(BOOL finished) {
}];
[self.view setNeedsLayout]; //更新視圖
[self.view layoutIfNeeded];
}
</code></pre>
下面來看下,如何刪除和增加約束
最后,附個(gè)addConstraint 函數(shù)的意義:
view1.attr1 = view2.attr2 * multiplier + constant
<pre><code>
[self.view removeConstraint:_sinaLeftDistance];//在父試圖上將iSinaButton距離屏幕左邊的約束刪除
NSLayoutConstraint *myConstraint =[NSLayoutConstraint
constraintWithItem:iSinaButton //子試圖
attribute:NSLayoutAttributeCenterX //子試圖的約束屬性
relatedBy:NSLayoutRelationEqual //屬性間的關(guān)系
toItem:self.view//相對(duì)于父試圖
attribute:NSLayoutAttributeCenterX//父試圖的約束屬性
multiplier:1.0
constant:0.0];// 固定距離
[self.view addConstraint: myConstraint];//為iSinaButton重新添加一個(gè)約束
</code></pre>
