if deltaY > 0, move the content down @param deltaY

perform refreshing UI

When the content view has reached top and refresh has been completed, view will be reset. @param frame

Do refresh complete work when time elapsed is greater than {@link #mLoadingMinTime}

Removes a previously-added footer view. @param v The view to remove @return true if the view was removed, false if the view was not a header view

Reset the progress spinner to default rotation, start and end angles.

@param scale Set the scale of the arrowhead for the spinner.

Set the colors the progress spinner alternates between. @param colors Array of integers describing the colors. Must be non-<code>null</code>.

@param strokeWidth Set the stroke width of the progress spinner in pixels.

显示正在加载中的布局

显示已经加载完成，没有更多数据的布局

显示普通布局

If at the top and not in loading, reset

Default implement for check can perform pull to refresh @param frame @param content @param header @return

content view, content view holder, header[0], header and footer placeholder(s) @return