很原始 很粗暴的寫法

定義輸入最大的字符數

#define MAX_LIMIT_NUMS 360

遵循<UITextViewDelegate>

@interface MineIntrduceVC ()<UITextViewDelegate>

// 沒有內容時候的 站位Lab
@property (weak, nonatomic) IBOutlet UILabel *placeHolderLab;

// 輸入框
@property (weak, nonatomic) IBOutlet UITextView *textInputView;

// 顯示當前輸入字符
@property (weak, nonatomic) IBOutlet UILabel *textNumLab;

別忘了遵循代理

    _textInputView.delegate = self;

代理方法

-(void)textViewDidBeginEditing:(UITextView *)textView{
    
    _placeHolderLab.hidden = YES;
    
}

- (void)textViewDidChange:(UITextView *)textView{
    
    //實時顯示字數
    self.textNumLab.text = [NSString stringWithFormat:@"%lu/360", (unsigned long)_textInputView.text.length];
    
    //字數限制操作
    if (_textInputView.text.length >= MAX_LIMIT_NUMS) {
        
        _textInputView.text = [textView.text substringToIndex:MAX_LIMIT_NUMS];
        
        _textNumLab.text = @"360/360";
        
    }
    
}