思路：

在整个View下面塞进一个高度为0的视图(使用低优先级约束)，当键盘改变时改变该View的高度即可。

constraint 有一个唯一可以修改的属性 constant，我承认它的名字确实很具有迷惑性。。。
以题主提到的高度问题为例，可以保存这个高度 constraint 的引用，在键盘出现和收起时

- (void)keyboardDidShowNotification
{
self.viewHeightConstraint.constant = 100.f;
[self.myView layoutIfNeed];
}

- (void)keyboardDidHideNotification
{
self.viewHeightConstraint.constant = 300.f;
[self.myView layoutIfNeed];
}

我的代码：

注册通知：

   1:   [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillChangeFrameNotification object:nil];

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

约束

@property (nonatomic,strong) NSLayoutConstraint* keyboardConstraint;

初始为0

   1:  self.keyboardConstraint = [NSLayoutConstraint constraintWithItem:self.keyboardView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:0];

   1:  - (void)keyboardWillShow:(NSNotification *)notification{

   2:      CGRect kbFrame = [[[notification userInfo] objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];

   3:      self.keyboardConstraint.constant = kbFrame.size.height;

   4:      [self.view addConstraint:self.keyboardConstraint];

   5:      //    [self.inputView needsUpdateConstraints];

   6:      [self.view setNeedsLayout];

   7:      [self.view layoutIfNeeded];

   8:      if (self.messages.count > 0){

   9:      NSIndexPath *idxP = [NSIndexPath indexPathForRow:(self.messages.count - 1) inSection:0];

  10:          [self.tableView scrollToRowAtIndexPath:idxP atScrollPosition:UITableViewScrollPositionBottom animated:YES];}

11:

  12:  }

13:

  14:  - (void)keyboardWillHidden{

15:

  16:      [self.view endEditing:YES];

  17:      [UIView animateWithDuration:0.25 animations:^{

  18:          //        self.keyboardConstraint.constant = 0;

  19:          self.keyboardConstraint.constant = 0;

  20:          //        [self.view removeConstraint:self.keyboardConstraint];

  21:          [self.view setNeedsLayout];

  22:          [self.view layoutIfNeeded];

  23:      }];

24:

  25:  }

lnum

iOS开发——使用Autolayout弹出键盘

思路：

我的代码：