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;}