iOS实现UITextView的placeholder和输入字数

相当于常见的反馈意见功能,要求有如下4点:

1.输入文字的时候提示文字消失，TextView没有文字的时候提示文字显示；
2.右下角实时显示字数；
3.字数到达指定限制后，TextView不能输入更多，可以删除；
4.提交按钮在TextView不为空的时候按钮为绿色且可点击；TextView为空时，为灰色状态且不可点击。

效果:

代码实现:

//  ViewController.m
//  DHTextViewSetting
//
//  Created by 邓昊 on 2017/12/7.
//  Copyright © 2017年 邓昊. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()<UITextViewDelegate>
@property (weak, nonatomic) IBOutlet UILabel *placeHolder;
@property (weak, nonatomic) IBOutlet UIButton *commitButton;
@property (weak, nonatomic) IBOutlet UITextView *feedBackTextView;
@property (weak, nonatomic) IBOutlet UILabel *stirngLenghLabel;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.feedBackTextView.delegate = self;
    self.placeHolder.userInteractionEnabled = NO;
    self.commitButton.userInteractionEnabled = NO;
    self.placeHolder.text = @"请输入您的意见...";
    
    self.feedBackTextView.layer.borderWidth = 0.5;
    self.feedBackTextView.layer.borderColor = [UIColor lightGrayColor].CGColor;
}

#pragma mark - UITextViewDelegate
//正在改变
- (void)textViewDidChange:(UITextView *)textView {
    NSLog(@"%@", textView.text);
    self.placeHolder.hidden = YES;
    //允许提交按钮点击操作
    self.commitButton.backgroundColor = [UIColor blueColor];
    self.commitButton.userInteractionEnabled = YES;
    //实时显示字数
    self.stirngLenghLabel.text = [NSString stringWithFormat:@"%lu/20", (unsigned long)textView.text.length];
    //字数限制操作
    if (textView.text.length >= 20) {
        textView.text = [textView.text substringToIndex:20];
        self.stirngLenghLabel.text = @"20/20";
    }
    //取消按钮点击权限，并显示提示文字
    if (textView.text.length == 0) {
        self.placeHolder.hidden = NO;
        self.commitButton.userInteractionEnabled = NO;
        self.commitButton.backgroundColor = [UIColor lightGrayColor];
    }
}

@end