simple form

ui.php

<?php

namespace ui;

use pocketmine\event\Listener;
use pocketmine\event\player\PlayerInteractEvent;
use pocketmine\event\player\PlayerJoinEvent;
use pocketmine\event\server\DataPacketReceiveEvent;
use pocketmine\item\Item;
use pocketmine\network\protocol\v120\ModalFormResponsePacket;
use pocketmine\network\protocol\v120\ShowModalFormPacket;
use pocketmine\Player;
use pocketmine\plugin\PluginBase;
use pocketmine\utils\TextFormat;

class main extends PluginBase implements Listener
{
    public function onEnable()
    {
        $this->getServer()->getPluginManager()->registerEvents($this, $this);
    }

    public function onJoin(PlayerJoinEvent $e)
    {
        $i = $e->getPlayer()->getInventory();
        $i->setItem(
            0, Item::get(331, 0, 1)->setCustomName(TextFormat::AQUA . "Sign in")
        );
        $i->setItem(
            1, Item::get(345, 0, 1)->setCustomName(TextFormat::GREEN . "Menu")
        );
        $i->setItem(
            2, Item::get(347, 0, 1)->setCustomName(
            TextFormat::GREEN . "Modal"
        )
        );
    }

    public function onTap(PlayerInteractEvent $e)
    {
        $player = $e->getPlayer();
        switch ($e->getItem()->getId()) {
            case 331:
                $data = [
                    'type'    => 'custom_form',
                    'title'   => 'Sign in',
                    'content' => [
                        [
                            "type" => "label",
                            "text" => "Sign in to your account."
                        ],
                        [
                            "type"        => "input",
                            "text"        => "login",
                            "placeholder" => "login",
                            "default"     => ""
                        ],
                        [
                            "type"        => "input",
                            "text"        => "password",
                            "placeholder" => "password",
                            "default"     => ""
                        ]
                    ]
                ];
                $this->createWindow($player, $data, 1);
                break;

            case 345:
                $data = [
                    'type'    => 'form',
                    'title'   => 'menu',
                    'content' => 'text',
                    'buttons' => [
                        ['text' => 'button #1'],
                        ['text' => 'button #2']
                    ]
                ];
                $this->createWindow($player, $data, 2);
                break;

            case 347:
                $data = [
                    'type'    => 'modal',
                    'title'   => "some question",
                    'content' => "Do you drink milk? XD",
                    'button1' => "yes",
                    'button2' => "no",
                ];
                $this->createWindow($player, $data, 3);
                break;
        }
    }

    public function onPickItem(DataPacketReceiveEvent $e)
    {
        $p = $e->getPlayer();
        $pk = $e->getPacket();
        if ($pk instanceof ModalFormResponsePacket) {
            $id = $pk->formId;
            $data = $pk->data;
            switch ($id) {
                case 1:
                    $login = "admin";
                    $pass = "12345";
                    if ($data == '[null,"' . $login . '","' . $pass . '"]' . "\n") {
                        $p->sendMessage("success!");
                    } else {
                        $p->sendMessage("wrong login or password error!");
                    }
                    break;

                case 2:
                    switch ($data) {
                        case 0:
                            $p->sendMessage("You clicked on button #1");
                            break;

                        case 1:
                            $p->sendMessage("You clicked on button #2");
                            break;
                    }
                    break;

                case 3:
                    switch ($data) {
                        case "true\n":
                            $p->sendMessage("You chose \"yes\"");
                            break;

                        case "false\n":
                            $p->sendMessage("You chose \"no\"");
                            break;
                    }
                    break;
            }
        }
    }

    public function createWindow(Player $player, $data, int $id)
    {
        $pk = new ShowModalFormPacket();
        $pk->formId = $id;
        $pk->data = json_encode(
            $data,
            JSON_PRETTY_PRINT | JSON_BIGINT_AS_STRING | JSON_UNESCAPED_UNICODE
        );
        $player->dataPacket($pk);
    }
}