图0 - 示例代码主界面

• 第一种，三方RPFloatingPlaceholders。用RPFloatingPlaceholderTextField 或者 RPFloatingPlaceholderTextView创建的textField 或 textView会得到这种效果。

  
  
  图1 - 第一种输入时的效果

创建一个 textField

CGRect frame = CGRectMake(20.f, 300.f, 273.f, 30.f);
RPFloatingPlaceholderTextField *flTextField =[[RPFloatingPlaceholderTextField alloc] initWithFrame:frame];
//弹上去时小字颜色
flTextField.floatingLabelActiveTextColor = [UIColor blueColor];
//placeholder 颜色
flTextField.floatingLabelInactiveTextColor = [UIColor grayColor];
flTextField.placeholder = @"您的账号";
flTextField.font = [UIFont fontWithName:@"Helvetica" size:16.f];
//另一种效果 默认为RPFloatingPlaceholderAnimateUpward
//    flTextField.animationDirection = RPFloatingPlaceholderAnimateDownward; // You can change animation direction
//    flTextField.text = @"I love lamp."; // You can set text after it's been initialized
[self.view addSubview:flTextField];

创建一个textView

CGRect frame2 = CGRectMake(20.f, 350.f, 273.f, 95.f);
    RPFloatingPlaceholderTextView *flTextView = [[RPFloatingPlaceholderTextView alloc] initWithFrame:frame2];
    flTextView.floatingLabelActiveTextColor = [UIColor blueColor];
    flTextView.floatingLabelInactiveTextColor = [UIColor grayColor];
    flTextView.placeholder = @"Tell me about yourself";
    flTextView.font = [UIFont fontWithName:@"Helvetica" size:16.f];
    flTextView.animationDirection = RPFloatingPlaceholderAnimateDownward;
    flTextView.text = @"I love lamp.  This is pre-existing text."; // You can set text after it's been initialized
    [self.view addSubview:flTextView];

• 第二种，和第一种意思差不多，个人觉得第二种效果稍微好一点。三方类：RPFloatingPlaceholders

  
  
  图2 - 第二种输入时的效果

创建一个textField

 //初始化一个textField
    JVFloatLabeledTextField *titleField = [[JVFloatLabeledTextField alloc] initWithFrame:CGRectMake(50, 200, kDeviceWidth-100, 30)];
    //textField类型
    titleField.borderStyle = UITextBorderStyleRoundedRect;
    titleField.font = [UIFont systemFontOfSize:16];
    //placeholder 的属性设置
    titleField.attributedPlaceholder =[[NSAttributedString alloc] initWithString:NSLocalizedString(@"Title", @"")attributes:@{NSForegroundColorAttributeName: [UIColor darkGrayColor]}];
    //弹上去的字体大小、颜色
    titleField.floatingLabelFont = [UIFont boldSystemFontOfSize:10];
    titleField.floatingLabelTextColor = [UIColor brownColor];
    //是否有清除按钮
    titleField.clearButtonMode = UITextFieldViewModeWhileEditing;
    [self.view addSubview:titleField];
    //这个属性是约束Autosizing控制，当打开约束的时候，要约束条件完全，否则可能试图丢失。
//    titleField.translatesAutoresizingMaskIntoConstraints = NO;
    titleField.keepBaseline = YES;
//    [titleField becomeFirstResponder];

创建一个textView

  //初始化textView
    JVFloatLabeledTextView *descriptionField = [[JVFloatLabeledTextView alloc] initWithFrame:CGRectMake(50, 300, kDeviceWidth-100, 100)];
    //textView placeholder字符串，字体大小，颜色
    descriptionField.font = [UIFont systemFontOfSize:16];
    descriptionField.placeholder = NSLocalizedString(@"Description hello my baby", @"");
    descriptionField.placeholderTextColor = [UIColor darkGrayColor];
    //弹上去时的大小，颜色
    descriptionField.floatingLabelFont = [UIFont boldSystemFontOfSize:10];
    descriptionField.floatingLabelTextColor = [UIColor brownColor];
    [self.view addSubview:descriptionField];
    descriptionField.translatesAutoresizingMaskIntoConstraints = NO;

• 第三，textField改变btn状态

  
  
  图3 - textField控制btn状态
  
  

  ~3.1 初始设置btn 灰色不可点击

[_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
_finishedBtn.userInteractionEnabled = NO;

~3.2 实现textField 代理方法

 - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    NSString *currentStr = [textField.text stringByReplacingCharactersInRange:range withString:string];
    [self changeButtonStatus:currentStr TF:textField _TF1:_nameTF _TF2:_phoneTF];
    return YES;
}

 - (BOOL)textFieldShouldClear:(UITextField *)textField{
    [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
    _finishedBtn.userInteractionEnabled = NO;
    return YES;
}

~3.3两个textField时的判定方法，当然多个textField时也是一个道理

 - (void)changeButtonStatus:(NSString *)str TF:(UITextField *)textField _TF1:(UITextField *)tf1 _TF2:(UITextField *)tf2
{
    if (textField == tf1) {
        if ([str length] != 0) {
            if (tf2.text.length != 0) {
                [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_blue"] forState:UIControlStateNormal];
                _finishedBtn.userInteractionEnabled = YES;
            }else {
                [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
                _finishedBtn.userInteractionEnabled = NO;
            }
        }else {
            [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
            _finishedBtn.userInteractionEnabled = NO;
        }
    }else if (textField == tf2) {
        if ([str length] != 0) {
            if (tf1.text.length != 0) {
                [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_blue"] forState:UIControlStateNormal];
                _finishedBtn.userInteractionEnabled = YES;
            }else {
                [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
                _finishedBtn.userInteractionEnabled = NO;
            }
        }else{
            [_finishedBtn setBackgroundImage:[UIImage imageNamed:@"btn_gray"] forState:UIControlStateNormal];
            _finishedBtn.userInteractionEnabled = NO;
        }
    }
}

#######示例代码链接：https://github.com/SPIREJ/SJTextFieldDemo