通过变量使用模型名称时,如何修复 class 模型未找到错误?

How can I fix class model not found error when using model name via variable?

当我在 Laravel 5.2 中使用此代码时:

use 'App\modelname';

public function test()
{
    $model = 'modelname';
    $db = $model::find(1);
    echo $db->id;
}

它不起作用,我收到此错误:

FatalThrowableError in HomeController.php line 541:
Class 'modelname' not found? 

我该如何解决?

我找到了答案:

public function test()
{
    $sh = "modelname";
    $model = "App\$sh";
    $db = $model::find(1);
    echo $db->id;
}