Laravel 5.2：您的要求无法解析为可安装的一组包（重复）

Question

我认为问题几乎相同，但错误是不同的。 我只是安装laravel 5.2并尝试安装quickadmin包。但我得到了这个错误。我也更新了作曲家。我尝试了this建议以及一些other建议。但它不起作用。我还尝试了旧版本的composer.json配置。但不幸的是，它无法正常工作。 的错误： 这是我的Composer.json配置，没有改变任何内容。

{
"name": "laravel/laravel",
"description": "The Laravel Framework.",
"keywords": ["framework", "laravel"],
"license": "MIT",
"type": "project",
"require": {
    "php": ">=5.5.9",
    "laravel/framework": "5.2.*"
},
"require-dev": {
    "fzaninotto/faker": "~1.4",
    "mockery/mockery": "0.9.*",
    "phpunit/phpunit": "~4.0",
    "symfony/css-selector": "2.8.*|3.0.*",
    "symfony/dom-crawler": "2.8.*|3.0.*"
},
"autoload": {
    "classmap": [
        "database"
    ],
    "psr-4": {
        "App\\": "app/"
    }
},
"autoload-dev": {
    "classmap": [
        "tests/TestCase.php"
    ]
},
"scripts": {
    "post-root-package-install": [
        "php -r \"copy('.env.example', '.env');\""
    ],
    "post-create-project-cmd": [
        "php artisan key:generate"
    ],
    "post-install-cmd": [
        "Illuminate\\Foundation\\ComposerScripts::postInstall",
        "php artisan optimize"
    ],
    "post-update-cmd": [
        "Illuminate\\Foundation\\ComposerScripts::postUpdate",
        "php artisan optimize"
    ]
},
"config": {
    "preferred-install": "dist"
}

}

如何在laravel 5.2中解决任何建议？