Artigo
11/18/2011

XmlReader.ReadElementContentAsBase64 Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Reads the element and decodes the Base64 content.

Namespace: System.Xml
Assembly: System.Xml (in System.Xml.dll)

Syntax

'Declaration
Public Overridable Function ReadElementContentAsBase64 ( _
    buffer As Byte(), _
    index As Integer, _
    count As Integer _
) As Integer

public virtual int ReadElementContentAsBase64(
    byte[] buffer,
    int index,
    int count
)

Parameters

buffer
Type: array<System.Byte[]
The buffer into which to copy the resulting text. This value cannot be nulla null reference (Nothing in Visual Basic).

index
Type: System.Int32
The offset into the buffer where to start copying the result.

count
Type: System.Int32
The maximum number of bytes to copy into the buffer. The actual number of bytes copied is returned from this method.

Return Value

Type: System.Int32
The number of bytes written to the buffer.

Exceptions

Exception	Condition
ArgumentNullException	The buffer value is nulla null reference (Nothing in Visual Basic).
InvalidOperationException	The current node is not an element node.
ArgumentOutOfRangeException	The index into the buffer or index + count is larger than the allocated buffer size.
NotSupportedException	The XmlReader implementation does not support this method.
XmlException	The element contains mixed-content.
FormatException	The content cannot be converted to the requested type.

Remarks

This method reads the element content, decodes it using Base64 encoding, and returns the decoded binary bytes (for example, an inline Base64-encoded GIF image) into the buffer. For more information, see RFC 1521, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies". You can obtain RFCs from the Request for Comments Web site.

ReadElementContentAsBase64 can only read simple-content elements. The element can contain text, white space, significant white space, CDATA sections, comments and processing instructions. It can also contain entity references, which are automatically expanded. The element cannot have child elements.

This method is very similar to the ReadContentAsBase64 method except that it can only be called on element node types.

If the count value is higher than the number of bytes in the document, or if it is equal to the number of bytes in the document, the XmlReader reads all the remaining bytes in the document and returns the number of bytes read. The next XmlReader method call returns a zero and moves the reader to the node following the EndElement.

If you call Read before all of the element content is consumed, the reader may behave as if the first content was consumed and then the Read method was called. This means that the reader will read all the text until the end element is encountered. It will then read the end tag node, read the next node, and then position itself on the next subsequent node.

Note:
The item delimiter for arrays is a single space. When deserializing arrays of type string, object, byte[], and Uri, the resulting array will contain an empty string value for any sequence of two delimiters (spaces) between non-empty values. For example, "a b", with two spaces, is deserialized as ["a", "", "b"]. This is different from other .NET Framework behavior and from all the other array types in which the empty values are ignored. You can use the following work-around to remove empty spaces: 1. Get the content as one big string instead of a string array from ReadContentAsString. 2. Use the System.String.Split method with StringSplitOptions.RemoveEmptyEntities to convert the big string into a string array. 3. Work with the resulting string array or convert each item further, for example, to Uri.

The item delimiter for arrays is a single space. When deserializing arrays of type string, object, byte[], and Uri, the resulting array will contain an empty string value for any sequence of two delimiters (spaces) between non-empty values. For example, "a b", with two spaces, is deserialized as ["a", "", "b"]. This is different from other .NET Framework behavior and from all the other array types in which the empty values are ignored.

You can use the following work-around to remove empty spaces:

1. Get the content as one big string instead of a string array from ReadContentAsString.

2. Use the System.String.Split method with StringSplitOptions.RemoveEmptyEntities to convert the big string into a string array.

3. Work with the resulting string array or convert each item further, for example, to Uri.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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