Where can I get a list of all iOS elements?
The Apple Developer portal has a document listing all the UI elements for iOS and also goes into what their various uses are. Here's an excerpt for how they describe a UITextView:
Text View A text view accepts and displays multiple lines of text. To learn more about defining a text view in your code, see UITextView Class Reference.
Appearance and Behavior A text view is a rounded rectangle of any height. A text view supports scrolling when the content is too large to fit inside its bounds.
If the text view supports user editing, a keyboard appears when the user taps inside the text view. The keyboard’s input method and layout are determined by the user’s language settings. When users tap the button labeled “.?123,” the keyboard changes to display numbers, punctuation marks, and a few common symbols.
Guidelines You have control over the font, color, and alignment of the text in a text view, but only as they apply to the entirety of the text. In other words, you can’t change any of these properties for only part of the text. The default font is the system font and the default color is black, because these tend to be the most readable. The default for the alignment property is left (you can change it to center or right).
If you must enable variable fonts, colors, or alignments within a view that displays text, you can use a web view instead of a text view, and style the text using HTML.
You can also specify different keyboard styles, depending on the type of content you expect users to enter. For a description of the styles you can use, see “Text Field.”
If you simply want to see a list of UI Elements and not the descriptions, go to the sidebar on the left and click on the disclosure arrow next to "iOS UI Elements Usage Guidelines", and it'll have a list of general categories like "Bars", "Content Views", "Controls", etc. From there you can click the disclosure arrow next to the category headings to see individual UI elements. The image below illustrates what I mean:
