计算文本的高度和调整文本内间距

CGSize size = [textView sizeThatFits:CGSizeMake(textViewW, CGFLOAT_MAX)];
CGSize size1 = [textView.text boundingRectWithSize:CGSizeMake(textViewW, CGFLOAT_MAX) options:NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName: [UIFont systemFontOfSize:14]} context:nil].size;
NSLog(@"sizeThatFits: %f \nboundingRectWithSize: %f", size.height, size1.height);
//Output: sizeThatFits: 100.000000  
//boundingRectWithSize: 83.535156

上面用两个方法计算文本高度只是为了方便比较，当然计算UITextView的高度最好的办法还是是使用sizeThatFits:计算，它并不改变UITextView的size，它只是让UITextView根据已有文本内容和给定size计算出UITextView的contentSize。那么是什么导致两个计算高度不一致，因为textView.textContainerInset默认值是UIEdgeInsetsMake(8, 0, 8, 0)，设置textView.textContainerInset = UIEdgeInsetsZero解决，再看下计算的高度值：

Output: sizeThatFits: 84.000000
boundingRectWithSize: 83.535156

计算结果基本接近，但是文本左右仍然有一定的间隔，此时可以使用lineFragmentPadding属性，通过设置textView.textContainer.lineFragmentPadding = 0可以去除左右间距，苹果API解释为在文本框每行的开头和结尾填充宽度默认为5，还是拿到值验证下：

CGFloat lineFragmentPadding = textView.textContainer.lineFragmentPadding;
UIEdgeInsets textContainerInset = textView.textContainerInset;
NSLog(@"lineFragmentPadding: %f\textContainerInset:%@", lineFragmentPadding, NSStringFromUIEdgeInsets(textContainerInset));
//Output: lineFragmentPadding: 5.000000
//textContainerInset:{8, 0, 8, 0}

占位符

第一种方法：使用将label添加在UITextView上利用delegate设置label的透明度来模仿UITextField占位符效果。这种方法使用起来虽然能达到占位占位符效果，但是多出用到UITextView时就用很多重复的代码，所以放弃使用此方法。

第二种方法：继承UITextView在其内部添加个UITextView

#import <UIKit/UIKit.h>

@interface PlaceholderTextView : UITextView

@property (nonatomic, strong) NSString *placeholder;

@property (nonatomic, strong) UIColor *placeholderColor;

@end

#import "PlaceholderTextView.h"

@interface PlaceholderTextView ()

@property (nonatomic, weak) UITextView *placeholderView;

@end

@implementation PlaceholderTextView

- (void)awakeFromNib {
    [super awakeFromNib];
    [self setup];
}

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        [self setup];
    }
    return self;
}

- (void)setup {
    self.scrollEnabled = NO;
    self.scrollsToTop = NO;
    self.showsHorizontalScrollIndicator = NO;
    self.enablesReturnKeyAutomatically = YES;
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:self];
}

- (void)textDidChange {
    self.placeholderView.hidden = self.text.length > 0;
}

- (UITextView *)placeholderView {
    if (_placeholderView == nil) {
        UITextField *textField = [[UITextField alloc] init];
        _placeholderColor = [textField valueForKeyPath:@"_placeholderLabel.textColor"];
        UITextView *placeholderView = [[UITextView alloc] init];
        placeholderView.frame = self.bounds;
        placeholderView.scrollEnabled = NO;
        placeholderView.showsHorizontalScrollIndicator = NO;
        placeholderView.showsVerticalScrollIndicator = NO;
        placeholderView.userInteractionEnabled = NO;
        placeholderView.font = self.font;
        placeholderView.textColor = _placeholderColor;
        placeholderView.backgroundColor = [UIColor clearColor];
        [self addSubview:placeholderView];
        _placeholderView = placeholderView;
    }
    return _placeholderView;
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor {
    _placeholderColor = placeholderColor;
    self.placeholderView.textColor = placeholderColor;
}

- (void)setPlaceholder:(NSString *)placeholder {
    _placeholder = placeholder;
    self.placeholderView.text = placeholder;
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

第三种方法：使用UITextView的Category实现占位符效果，本来是打算自己实现的，但是在github上看到一个别出心裁的UITextView-Placeholder方法，巧妙的运用Method Swizzling、关联属性、KVO等方法实现了占位符功能，不要吝啬使用方法，推荐使用这种方法。

限制最大行数

根据行数计算出textView的最大高，每行高度 * 总行数 + 文字上下间距。

maxTextHeight = ceil(textView.font.lineHeight * maxNumberOfLines + textView.textContainerInset.top + textView.textContainerInset.bottom);

适应文字高度

- (void)textViewDidChange:(UITextView *)textView {
    NSInteger height = ceilf([textView sizeThatFits:CGSizeMake(textView.bounds.size.width, MAXFLOAT)].height);
    if (textHeight != height) {
        textView.scrollEnabled = height > maxTextHeight && maxTextHeight> 0;
        textHeight = height;
        if (textView.scrollEnabled == NO) {
            self.textViewConstraintH.constant = height;
            [self.view layoutIfNeeded];
        }
    }
}

随键盘弹出效果

1、添加监听

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

2、处理键盘位置变化

- (void)keyboardWillChangeFrame:(NSNotification *)note {
    CGRect endFrame = [note.userInfo[UIKeyboardFrameEndUserInfoKey] CGRectValue];
    CGFloat duration = [note.userInfo[UIKeyboardAnimationDurationUserInfoKey] floatValue];
    CGFloat screenH = [UIScreen mainScreen].bounds.size.height; 
    _bottomCons.constant = endFrame.origin.y != screenH?endFrame.size.height:0;
    [UIView animateWithDuration:duration animations:^{
        [self.view layoutIfNeeded];
    }];
}