IOS代码笔记UIView的placeholder的效果

#import <UIKit/UIKit.h>

@interface RootViewController : UIViewController
<UITextViewDelegate>
{
  UITextView *psTextView;
  UILabel *pslabel;
}
@end 

#import "RootViewController.h"

@interface RootViewController ()

@end

@implementation RootViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
  self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
  if (self) {
    // Custom initialization
  }
  return self;
}

- (void)viewDidLoad
{
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  
  self.title=@"UIView的placeholder的效果";
  
  [self initBackgroundView];

}
#pragma -mark -初始化背景图
-(void)initBackgroundView
{
  UIView *backView=[[UIView alloc]initWithFrame:CGRectMake(0, 0, 320, 480)];
  [self.view addSubview:backView];
  
  psTextView=[[UITextView alloc]initWithFrame:CGRectMake(10, 70, 280, 200)];
  psTextView.text=@"";
  psTextView.backgroundColor=[UIColor yellowColor];
  psTextView.delegate=self;
  psTextView.scrollEnabled=NO;
  [backView addSubview:psTextView];
  
  
  pslabel=[[UILabel alloc]initWithFrame:CGRectMake(15, 140, 280, 20)];
  pslabel.text=@"请输入备注信息";
  pslabel.textColor=[UIColor grayColor];
  pslabel.enabled=NO;
  pslabel.backgroundColor=[UIColor clearColor];
  [backView addSubview:pslabel];

}
#pragma -mark -UITextView Delegate
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView
{
  return YES;
}
-(BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
  
  if (text.length>0) {
    pslabel.hidden=YES;
  }
  
  if ([text isEqualToString:@"\n"]) {
    [textView resignFirstResponder];
    return NO;
  }
  
  return YES;
}