自定义UITextView

#import "ViewController.h"
#import "YMTextView.h"

@interface ViewController ()
//输入控件
@property (nonatomic, weak) YMTextView *textView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self setupLabel];
    
    //设置输入控件
    [self setupTextView];
    
}

-(void)setupLabel {
    UILabel *titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 40, self.view.frame.size.width, 44)];
    titleLabel.text = @"自定义textView控件";
    titleLabel.textAlignment = NSTextAlignmentCenter;
    titleLabel.textColor = [UIColor blackColor];
    [self.view addSubview:titleLabel];
}

//添加输入控件
-(void)setupTextView {
    // 在这个控制器中，textView的contentInset.top默认会等于64
    YMTextView *textView = [[YMTextView alloc] init];
    textView.frame = CGRectMake(0, 100, self.view.frame.size.width, 200);
    textView.backgroundColor = [UIColor lightGrayColor];
    textView.font = [UIFont systemFontOfSize:15];
    //设置占位文字
    textView.placeholder = @"这里是占位文字...";
    //设置占位文字颜色
//    textView.placeholderColor = [UIColor redColor];
    [self.view addSubview:textView];
    self.textView = textView;
    //监听通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:textView];
}
/**
 *  监听文字改变
 */
-(void)textDidChange {
    
    if (self.textView.hasText) {
        NSLog(@"文字发生改变----%@",self.textView.text);
    }
}

-(void)dealloc {
    //移除通知
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

#import <UIKit/UIKit.h>

@interface YMTextView : UITextView
/**
 *  占位文字
 */
@property (nonatomic, copy) NSString *placeholder;
/**
 *  占位文字颜色
 */
@property (nonatomic, strong) UIColor *placeholderColor;

@end

#import "YMTextView.h"

@implementation YMTextView


- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // 当UITextView的文字发生改变时，UITextView自己会发出一个UITextViewTextDidChangeNotification通知
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

/**
 *  监听文字改变
 */
-(void)textDidChange {
    
    //重绘
    [self setNeedsDisplay];
    
}

-(void)setPlaceholder:(NSString *)placeholder {
    _placeholder = placeholder;
    // setNeedsDisplay会在下一个消息循环时刻，调用drawRect:
    [self setNeedsDisplay];
}

-(void)setText:(NSString *)text {
    [super setText:text];
    // setNeedsDisplay会在下一个消息循环时刻，调用drawRect:
    [self setNeedsDisplay];
}

-(void)setFont:(UIFont *)font {
    [super setFont:font];
    // setNeedsDisplay会在下一个消息循环时刻，调用drawRect:
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
    
    // 如果有输入文字，就直接返回，不画占位文字
    if (self.hasText) return;
    //设置文字属性
    NSMutableDictionary *attributes = [NSMutableDictionary dictionary];
    attributes[NSFontAttributeName] = self.font;
    attributes[NSForegroundColorAttributeName] = self.placeholderColor ? self.placeholderColor : [UIColor grayColor];
    //画文字
    CGFloat x = 5;
    CGFloat width = rect.size.width -2 * x;
    CGFloat y = 8;
    CGFloat height = rect.size.height - 2 * y;
    CGRect placeholderRect = CGRectMake(x, y, width, height);
    [self.placeholder drawInRect:placeholderRect withAttributes:attributes];
}

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

@end