1、修改某个UITextField的键盘的返回键类型：
[_bottomTextView setReturnKeyType:UIReturnKeyDone];
1.1、textFied点击return键之后有处理方法：
UITextViewDelegate里面有这样一个代理函数：
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)tex
1.2、textView点击return键之后的处理：
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
if ([text isEqualToString:@" "]){ //判断输入的字是否是回车，即按下return
//在这里做你响应return键的代码
[self.rejectReasonTextView resignFirstResponder];
return NO; //这里返回NO，就代表return键值失效，即页面上按下return，不会出现换行，如果为yes，则输入页面会换行
}
return YES;
}
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以及监听键盘的高度变化，一起随着键盘顶出来或者压下去：
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(keyboardHeightChange:) name:UIKeyboardWillChangeFrameNotification object:nil];
keyboardHeightChange：
-(void)keyboardHeightChange:(NSNotification *)notifi
{
self.dropButton.hidden = YES;
NSDictionary *dict=[notifi userInfo];
CGRect keyBoardRect=[[dict objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
CGFloat keyBoardHeight=keyBoardRect.size.height;
CGFloat keyBoardY=keyBoardRect.origin.y;
float animationDuration = [[dict objectForKey:UIKeyboardAnimationDurationUserInfoKey] floatValue];//取到键盘动画退出弹出的时间，好处，不同的键盘时间可能不一样
[UIView animateWithDuration:animationDuration animations:^{
CGRect bottomNewFrame=CGRectMake(_bottomView.frame.origin.x, keyBoardY+_bottomView.frame.size.height, _bottomView.frame.size.width, _bottomView.frame.size.height);
_bottomView.frame=bottomNewFrame;
}];