error during deploying custom theme in magento 2

Question

i am working on theme in magento 2,but i am getting error in terminal(CMD),the error message is "unable to load theme by specified key:My/Helloworld" when i run php bin\magento setup:static-content:deploy, my required file are app\design\frontend\My\Helloworld\composer.json

{
    "name": "magento/theme-frontend-My",
    "description": "N/A",
    "require": {
        "php": "~5.5.0|~5.6.0|~7.0.0",
        "magento/theme-frontend-blank": "100.0.*",
        "magento/framework": "100.0.*"
    },
    "type": "magento2-theme",
    "version": "100.0.1",
    "license": [
        "OSL-3.0",
        "AFL-3.0"
    ],
    "autoload": {
        "files": [
            "registration.php"
        ]
    }
}

app\design\frontend\My\Helloworld\registration.php

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::THEME,
    'frontend/My/Helloworld',
    __DIR__
);

Answer 1

A common oversight which could throw this error is forgetting to run:

bin/magento setup:upgrade

This allows Magento to register your theme in the 'theme' table of the Magento database. You can check if your theme is registered via the mysql command line:

mysql> use <your magento database>;
mysql> SELECT * FROM theme;

If your theme is registered also make sure that the 'type' column value for your theme record is 0. Values of 1 can also lead to this error.

Answer 2

have you declare theme name from di.xml like below. Below code is the example for creating backend.

<type name="Magento\Theme\Model\View\Design">
    <arguments>
        <argument name="themes" xsi:type="array">
            <item name="frontend" xsi:type="string">Magento/luma</item>
            <item name="adminhtml" xsi:type="string">Learning/backend</item>
        </argument>
    </arguments>
</type>

and run the below commands in CLI

1. php bin/magento cache:clean
2. php bin/magento setup:upgrade
3. php bin/magento setup:static-content:deploy

if still not working go to admin panel clear the cache and clear the flush and re run above commands it will work.

Answer 3

I have the same issue, this may be due to cache files

Remove following directories pub/static, var/cache, var/composer_home, var/generation, var/page_cache,var/view_preprocessed

Then run the following command line from terminal/shell: php bin/magento setup:static-content:deploy