Class PageStreamer<TResource, TRequest, TResponse, TToken>

A page streamer is a helper to provide both synchronous and asynchronous page streaming of a listable or queryable resource.

Inheritance

System.Object

PageStreamer<TResource, TRequest, TResponse, TToken>

Inherited Members

System.Object.Equals(System.Object)

System.Object.Equals(System.Object, System.Object)

System.Object.GetHashCode()

System.Object.GetType()

System.Object.MemberwiseClone()

System.Object.ReferenceEquals(System.Object, System.Object)

System.Object.ToString()

Namespace: Google.Apis.Requests

Assembly: Google.Apis.dll

Syntax

public sealed class PageStreamer<TResource, TRequest, TResponse, TToken>
    where TRequest : IClientServiceRequest<TResponse> where TToken : class

Type Parameters

Name	Description
TResource	The type of resource being paginated
TRequest	The type of request used to fetch pages
TResponse	The type of response obtained when fetching pages
TToken	The type of the "next page token", which must be a reference type; a null reference for a token indicates the end of a stream of pages.

Remarks

The expected usage pattern is to create a single paginator for a resource collection, and then use the instance methods to obtain paginated results.

Examples

To construct a page streamer to return snippets from the YouTube v3 Data API, you might use code such as the following. The pattern for other APIs would be very similar, with the request.PageToken, response.NextPageToken and response.Items properties potentially having different names. Constructing the page streamer doesn't require any service references or authentication, so it's completely safe to perform this in a type initializer.

using Google.Apis.YouTube.v3;
using Google.Apis.YouTube.v3.Data;
...
private static readonly snippetPageStreamer = new PageStreamer<SearchResult, SearchResource.ListRequest, SearchListResponse, string>(
    (request, token) => request.PageToken = token,
    response => response.NextPageToken,
    response => response.Items);

Constructors

PageStreamer(Action<TRequest, TToken>, Func<TResponse, TToken>, Func<TResponse, IEnumerable<TResource>>)

Creates a paginator for later use.

Declaration

public PageStreamer(Action<TRequest, TToken> requestModifier, Func<TResponse, TToken> tokenExtractor, Func<TResponse, IEnumerable<TResource>> resourceExtractor)

Parameters

Type	Name	Description
System.Action<TRequest, TToken>	requestModifier	Action to modify a request to include the specified page token. Must not be null.
System.Func<TResponse, TToken>	tokenExtractor	Function to extract the next page token from a response. Must not be null.
System.Func<TResponse, System.Collections.Generic.IEnumerable<TResource>>	resourceExtractor	Function to extract a sequence of resources from a response. Must not be null, although it can return null if it is passed a response which contains no resources.

Methods

Fetch(TRequest)

Lazily fetches resources a page at a time.

Declaration

public IEnumerable<TResource> Fetch(TRequest request)

Parameters

Type	Name	Description
TRequest	request	The initial request to send. If this contains a page token, that token is maintained. This will be modified with new page tokens over time, and should not be changed by the caller. (The caller should clone the request if they want an independent object to use in other calls or to modify.) Must not be null.

Returns

Type	Description
System.Collections.Generic.IEnumerable<TResource>	A sequence of resources, which are fetched a page at a time. Must not be null.

FetchAllAsync(TRequest, CancellationToken)

Asynchronously (but eagerly) fetches a complete set of resources, potentially making multiple requests.

Declaration

public async Task<IList<TResource>> FetchAllAsync(TRequest request, CancellationToken cancellationToken)

Parameters

Type	Name	Description
TRequest	request	The initial request to send. If this contains a page token, that token is maintained. This will be modified with new page tokens over time, and should not be changed by the caller. (The caller should clone the request if they want an independent object to use in other calls or to modify.) Must not be null.
System.Threading.CancellationToken	cancellationToken

Returns

Type	Description
System.Threading.Tasks.Task<System.Collections.Generic.IList<TResource>>	A sequence of resources, which are fetched asynchronously and a page at a time.