How to collapse all methods in Xcode?

X-Code 7 onwards

To collapse all method : Shift + Option + Command + Left arrow

To expand all method : Shift + Option + Command + Right arrow

Updates in Xcode 10

Xcode 10 has increased support for code folding, including:

1. A new code folding ribbon showing all of the multi-line foldable blocks of code in the editor
2. A new style for folded code in the editor that allows you to edit lines with folded code
3. Support for folding any block of code enclosed in curly braces
4. Support for folding blocks of code from the folding ribbon, from structured selection, or from the

Menubar ► Editor ► Code Folding ► Fold menu item

Look at this snapshot:

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Code folding was disabled in Xcode 9 beta 1, which is working now, in Xcode 9 Beta5 according to beta release note: Resolved in Xcode 9 beta 5 – IDE

Here is how:

1. Press and hold ⌘ (command) button in keyboard and move/hover mouse cursor on any (start or end) braces. It will automatically highlight, block area.
2. Keep (hold) ⌘(command) button in pressed condition and click on highlighted area. It will enable quick menu popover window with Fold option.
3. Select Fold from menu list. It will fold your code and shows 3 dots, folding/covering entire block.
4. Now, to again unfold your code block, release ⌘ (command) button and click on 3 dots folding a block.

For easy understanding, look at this snapshot:

It's all keyboard short cuts are also working.

Fold                          ⌥ ⌘ ←      option + command + left arrow
Unfold                        ⌥ ⌘ →      option + command + right arrow
Unfold All                    ⌥ U        option + U
Fold Methods & Functions      ⌥ ⌘ ↑      option + command + up arrow
Unfold Methods & Functions    ⌥ ⌘ ↓      option + command + down arrow
Fold Comment Blocks           ⌃ ⇧ ⌘ ↑    control + shift + command + up
Unfold Comment Blocks         ⌃ ⇧ ⌘ ↓    control + shift + command + down
Focus Follows Selection       ⌃ ⌥ ⌘ F    control + option + command + F
Fold All                      ⌘ ⌥ ⇧ ←    command + option + shift + left
Unfold All                    ⌘ ⌥ ⇧ →    command + option + shift + left

Code folding options from Xcode Menu:

Menubar ▶ Editor ▶ Code Folding ▶ "Here is list of code folding options"

Here is ref snapshot:

Same options from Xcode Short-cut list:

Menubar ▶ Xcode ▶ Preferences ▶ Key Bindings ▶ "Here is list of code folding short-keys"

I like this table from Krunal's answer (above) : https://stackoverflow.com/a/46020397/1554947

Fold                          ⌥ ⌘ ←      option + command + left arrow
Unfold                        ⌥ ⌘ →      option + command + right arrow
Fold Methods & Functions      ⌥ ⌘ ↑      option + command + up arrow
Unfold Methods & Functions    ⌥ ⌘ ↓      option + command + down arrow
Fold Comment Blocks           ⌃ ⇧ ⌘ ↑    control + shift + command + up
Unfold Comment Blocks         ⌃ ⇧ ⌘ ↓    control + shift + command + down
Focus Follows Selection       ⌃ ⌥ ⌘ F    control + option + command + F
Fold All                      ⌘ ⌥ ⇧ ←    command + option + shift + left
Unfold All                    ⌘ ⌥ ⇧ →    command + option + shift + right

As of Xcode 4 it seems to have changed.

command-alt-shift-left arrow will do the trick...

To fold/unfold current methods or if structures use:

Fold: command-alt-left arrow

Unfold: command-alt-right arrow