Added in [API level 8](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

# XPathFunctionResolver

` public interface XPathFunctionResolver `   
` `

|---|
| javax.xml.xpath.XPathFunctionResolver |

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*** ** * ** ***

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`XPathFunctionResolver` provides access to the set of user defined `XPathFunction`s.

XPath functions are resolved by name and arity. The resolver is not needed for XPath built-in functions and the resolver ***cannot*** be used to override those functions.

In particular, the resolver is only called for functions in an another namespace (functions with an explicit prefix). This means that you cannot use the `XPathFunctionResolver` to implement specifications like [XML-Signature Syntax and Processing](http://www.w3.org/TR/xmldsig-core/) which extend the function library of XPath 1.0 in the same namespace. This is a consequence of the design of the resolver.

If you wish to implement additional built-in functions, you will have to extend the underlying implementation directly.

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**See also:**

- [XML Path Language (XPath) Version 1.0, Core Function Library](http://www.w3.org/TR/xpath#corelib)

## Summary

| ### Public methods ||
|---|---|
| ` abstract https://developer.android.com/reference/javax/xml/xpath/XPathFunction` | ` https://developer.android.com/reference/javax/xml/xpath/XPathFunctionResolver#resolveFunction(javax.xml.namespace.QName,%20int)(https://developer.android.com/reference/javax/xml/namespace/QName functionName, int arity) ` <br /> Find a function in the set of available functions. |

## Public methods

### resolveFunction

Added in [API level 8](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public abstract XPathFunction resolveFunction (QName functionName, 
                int arity)
```

<br />

Find a function in the set of available functions.

If `functionName` or `arity` is `null`, then a `NullPointerException` is thrown.

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| Parameters ||
|---|---|
| `functionName` | `QName`: The function name. <br /> |
| `arity` | `int`: The number of arguments that the returned function must accept. <br /> |

| Returns ||
|---|---|
| `https://developer.android.com/reference/javax/xml/xpath/XPathFunction` | The function or `null` if no function named `functionName` with `arity` arguments exists. <br /> |

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/NullPointerException` | If `functionName` or `arity` is `null`. |