为什么表单中的字段不打印？

When the data from the following form is submitted to action.php, it prints the second variable date of the form but gives an error for the first and third field. Why is that ?

HTML:

      <form method="post" action="./action.php">

            <span id="type_tweet">Type your tweet</span>
            <span>
                <textarea rows="4" cols="80" id="tweet_entered"> </textarea>
            </span>
            <hr />
            <span>When to tweet</span>

            <span id="date"> <!-- Date -->
                <input type="text" name="SelectedDate" id="SelectedDate" readonly onClick="GetDate(this);">
            </span> 

            <span id="at">@</span>

            <span id="time"> <!-- Time-->
                <input type="text" class="timepicker" name="SelectedTime" id="timepicker" />
            </span>
            <span>
                <input type="submit" value="submit"  id="schedule_button" />
            </span>
     </form>

PHP: (action.php)

<?php
    echo $_POST["tweet_entered"];
    echo "<br />";
    echo $_POST["SelectedDate"];
    echo "<br />";
    echo $_POST["timepicker"];
    echo "<br />";
?>

Errors when action.php is run :

Notice: Undefined index: tweet_entered in E:\Installed_Apps\xampp\htdocs\twibuffer\action.php on line 2

4/29/2014

Notice: Undefined index: timepicker in E:\Installed_Apps\xampp\htdocs\twibuffer\action.php on line 6

You need to change this

<textarea rows="4" cols="80" id="tweet_entered"> </textarea>

to

<textarea rows="4" cols="80" id="tweet_entered" name="tweet_entered"> </textarea>

and

<input type="text" class="timepicker" name="SelectedTime" id="timepicker" />

to

<input type="text" class="timepicker" name="timepicker" id="timepicker" />

The name attribute is what gets loaded into the $_POST variable