XForms XPath函數使用手冊

時間 2019-12-06

標籤 xforms xpath 函數使用手冊简体版

原文原文鏈接

1. 概要

本文所描述的全部函數爲XForms 1.1所提供的xpath函數，這些函數只能在GForms的xpath編輯器中可用，這樣才能在運行時識別並執行。node

不可在XMLUtil、標準XML DOM中使用這些函數。web

GForms平臺提供xpath編輯器，該編輯器能夠協助開發者完成大多數xpath表達式開發：正則表達式

2. 節點函數

2.1. instance

node-set instance(string?)算法

An XForms Model can contain more than one instance. This function allows access to instance data, within the same XForms Model, but outside the instance data containing the context node.express

If the argument is omitted or is equal to the empty string, then the root element node (also called the document element node) is returned for the default instance in the model that contains the current context node.編程

Otherwise, the argument is converted to a string as if by a call to the string function. This string is treated as an IDREF, which is matched against instance elements in the containing document. If a match is located, and the matching instance data is associated with the same XForms Model as the current context node, this function returns a node-set containing just the root element node (also called the document element node) of the referenced instance data. In all other cases, an empty node-set is returned.後端

Example:app

For instance data corresponding to this XML:less

 1 <xforms:instance xmlns="" id="orderform"> 2  3 <orderForm> 4  5 <shipTo> 6  7 <firstName>John</firstName> 8  9 </shipTo>10 11 </orderForm>12 13 </xforms:instance>

The following expression selects the firstName node. Note that the instance function returns an element node, effectively replacing the leftmost location step from the path:dom

ref="instance('orderform')/shipTo/firstName"

3. 字符串函數

3.1. if

string if(boolean, string, string)

Function if evaluates the first parameter as boolean, returning the second parameter when true, otherwise the third parameter.

3.2. property

string property(string)

This function accepts a string identifying a property name. If the property name is not recognized, empty string is returned. The property definitions for this function are as follows:

Property	Return Value
version	1.1
conformance-level	full, basic or a string beginning with full or basic
Any other NCName	Reserved. Their use results in an exception (see 7.5 The XForms Function Library for the exception type)
QNameButNotNCName	An implementation-specific property value, such as a locale or timezone for the user agent. If the implementation does not support the property, then empty string is returned.

Examples:

property('version')

returns 1.1

property('conformance-level')

may return full

4. 數值函數

4.1. avg

number avg(node-set)

Function avg returns the arithmetic average of the result of converting the string-values of each node in the argument node-set to a number. The sum is computed with sum(), and divided with div by the value computed with count(). If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

4.2. The min() Function

number min(node-set)

Function min returns the minimum value of the result of converting the string-values of each node in argument node-set to a number. "Minimum" is determined with the < operator. If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

4.3. max

number max(node-set)

Function max returns the maximum value of the result of converting the string-values of each node in argument node-set to a number. "Maximum" is determined with the < operator. If the parameter is an empty node-set, or if any of the nodes evaluate to NaN, the return value is NaN.

4.4. count-non-empty

number count-non-empty(node-set)

Function count-non-empty returns the number of non-empty nodes in argument node-set. A node is considered non-empty if it is convertible into a string with a greater-than zero length.

4.5. index

number index(string)

Function index takes a string argument that is the IDREF of a repeat and returns the current 1-based position of the repeat index for the identifiedrepeat—see 9.3.1 The repeat Element for details on repeat and its associated repeat index. If the specified argument does not identify a repeat, the function returns NaN.

Note:

The IDREF obtained from the function parameter may not uniquely identify the desired repeat if the repeat element bearing the matching ID resides in a repeating construct such as element repeat. The general method described in 4.7 Resolving ID References in XForms is used to determine the desired run-time repeat object.

index

<xforms:trigger><xforms:label>Add to Shopping Cart</xforms:label><xforms:insert ev:event="DOMActivate" position="after"nodeset="items/item" at="index('cartUI')"/></xforms:trigger>

4.6. power

number power(number, number)

Raises the first argument to the power of the second argument, returning the result. If the calculation does not result in a real number, then NaNis returned.

Examples:

power(2, 3)

returns 8

power(-1, 0.5)

returns NaN.

if (prin>0 and dur>0 and rate>0, prin*rate/(1-power(1+rate, -dur)), 0)

returns a compounded interest payment value given a non-zero principal (prin), duration (dur) and periodic interest rate (rate).

4.7. random

number random(boolean?)

This function generates and returns a uniformly distributed random or pseudorandom number in the range from 0.0 up to but excluding 1.0. This function accepts an author-optional boolean parameter that is false by default. If true, the random number generator for this function is first seeded with a source of randomness before generating the return value. A typical implementation may seed the random number generator with the current system time in milliseconds when random(true) is invoked, and it may apply a linear congruential formula to generate return values on successive invocations of the function.

Example:

random()

could return 0.14159265358979

4.8. compare

number compare(string, string)

This function returns -1, 0, or 1, depending on whether the value of the first argument is respectively less than, equal to, or greater than the value of second argument based on lexicographic comparison using Unicode code point values [Unicode Collation Algorithm].

Example:

compare('apple', 'orange')

returns -1

5. 布爾函數

5.1. boolean-from-string

boolean boolean-from-string(string)

Function boolean-from-string returns true if the required parameter string is "true" or "1", or false if parameter string is "false", or "0". This is useful when referencing a Schema xsd:boolean datatype in an XPath expression. If the parameter string matches none of the above strings, according to a case-insensitive comparison, the return value is false.

6. 時間函數

時間的格式處理，爲了簡化本地化時間處理，gforms提供對時間的格式進行了可配置處理，按照xsd:date、xsd:dateTime，時間的字符串中會包含T、z等字符串信息，而在大多數編程場景下，通常不須要處理T、z信息，因此爲了提供編程開發人員處理時間的效率，GForms對xsd:dateTime的合法格式進行可配置化。

系統默認時間格式：