5. Html form tag_html/css_WEB-ITnose

The main function of form and form controls is to collect user experience. When the user submits the form, the content entered by the user will be submitted to the remote server as request parameters.

1, form tag

: Create a form. This element will not generate a visual interface, but other controls must be placed in this tag. Commonly used attributes:
action: This attribute is required and is used to specify the address to which the form is submitted when the confirmation button of the stand-alone form is used. It can be an absolute address or a relative address.
method: used to specify what type of request to send when submitting a form, which can be get or post. The difference between get and post is mentioned in my http blog, so I won’t go into details here.
enctype: used to specify the character set used when encoding form content. By default, form data is encoded as "application/x-www-form-urlencoded": that is, all characters are encoded before being sent to the server (spaces are converted to " " plus signs, special characters are converted to ASCII HEX values )
There are three attribute values ​​for this attribute:
application/x-www-form-urlencoded: Encode all characters before sending (default)
multipart/form-data: Do not encode characters, use This value must be used when a form contains a file upload control.
text/plain spaces are converted to " " plus signs, but special characters are not encoded.
name: The unique name of the form, it is recommended to keep the same as the id.
Target: How to open the url, _self, _blank, _top, _parent.
Regarding this form tag, one thing that needs to be emphasized is how the form control is converted into the corresponding request parameter. The specific rules are as follows:
1. Each form control with a name attribute corresponds to a request parameter, and there is no name attribute. The form control will not generate request parameters. If multiple form controls repeat a name attribute value, then only one request parameter will be generated, but this parameter has multiple values.
2. The name attribute of the form control specifies the request parameter name, and the value specifies the request parameter value.
3. If a form control sets the disabled="disabled" attribute, this form control will no longer generate request parameters.

2, input tag

element is the most versatile among form controls. The following input elements are generated through this tag . This tag is an empty tag.
1. Single-line text box: type="text"
2. Password input box: type="password"
3. Hidden field: type="hidden"
4. Radio button: type="radio"
5. Check box: type="checkbox"
6. Image field: type="image"
7. File upload field: type="file"
8 , submit, reset, no action button: type="submit", type="reset", type="button"
The element can specify core attributes such as id, style, class, etc., and can also specify Onclick, onfocus, onblur and other event attributes are as follows:
1. checked, used to set whether single selection and multi-selection are selected
2. disabled, used to disable this element
3. maxlength, used to specify the maximum number of characters allowed to be entered in the text box
4. readonly, read-only mode, cannot be modified
5. size, specifies the width of the element
6. src, image domain display The url of the image
7. align, the alignment of the image field
The following is an html containing the above elements:

<title>表单相关标签</title>

单行文本框：
不能编辑的文本框：
密码框：
隐藏域：
单选：男女
多选：男女
文件上传域：
图像域：
4个按钮：

3. List box and drop-down menu

is used to create list boxes and drop-down menus. This element must be used in conjunction with . Each represents a list item or a menu item
Frequently used 2 attributes, disabled, are used to disable the list box and drop-down menu.
multiple: used to set whether to select multiple items.
It is worth noting that whether a generates a list box or a drop-down menu is determined by the above two elements. If size or multiple is specified, then a list box is generated, otherwise it is a drop-down menu.
: An option. value represents the request parameter value, disabled is whether this option is disabled, selected, whether this option is selected
: an option group. label, required, used to specify the label of this option group.
The following is an html containing the above tags:

<title>下拉相关标签</title>	

下拉： 林肯 夜愿 列表框1： 林肯 夜愿 列表框2： 林肯 夜愿 美国 芬兰

4. Use textarea to define the text area

: use To define a multi-line text field in HTML, two attributes are required, cols and rows, which are used to specify the width and height of the text field. The multi-line text field is special. In addition to the ordinary event attributes, it can also specify the onselect attribute, which is used to indicate the event when the content in the text field is selected. <br> 与单行文本框相同的是，<textarea>元素也应该指定name属性，该属性将作为textarea的请求参数名，与单行文本框不同的是，<textarea>不能指定value属性，<textarea>之间的内容将作为所对应的请求参数的参数值。
关于这个标签还是经常会用到的，在以前我写表单的时候，将单行的文本框拉长拉宽，但是我们在输入的时候也只能是一行，不能换行的，忽忽。
以下是包含这个标签的一份html：

<title>多行文本框相关标签</title>	

单行文本框：
多行文本框：

5，使用label定义标签

用于在表单元素中定义标签，这些标签只是对其他可以生成请求参数的控件来做说明的，本身是不会产生请求参数的，所以不要为元素指定value的属性值。
从表面上看，元素只是输出普通文本，其实他最大的作用就是，当我们点击生成的文本时，他说关联的表单控件将自动获得焦点。
让标签和表单控件关联有2种方式：
1，隐式使用for属性：设置标签的for属性指向所关联表单控件的id属性值。
2，显式关联：将普通文本，表单控件丢在标签内部就可以了。关于这2种方式推荐使用第一种，也就是使用for来隐式关联，因为后面一种可能在ie下不兼容。
以下是包含上面标签的一份html：

<title>label相关标签</title>	

单行文本框：
多行文本框：

6，使用button定义按钮

元素用于定义一个按钮，在这个标签的内部可以包含普通的文本，文本格式化标签，图像等内容，这也就是和按钮的不同之处。
这个标签使用不多，最多就是在一个按钮做成图像格式的才会用到。以下是一份html：

<title>button相关标签</title>