Multiline string for TextFormString validator

You can add more than 1 line to your TextFormFiled error label by using the errorMaxLines property in the InputDecoration:

errorMaxLines: 2

For example:

TextFormField(
    decoration: const InputDecoration(
    icon: Icon(Icons.person),
    hintText: 'What do people call you?',
    labelText: 'Name *',
    errorMaxLines: 2
    ),
    validator: (String value) {
    return value.contains('@')
        ? 'Do not use the @ char. Do not use the @ char. Do not use the @ char. Do not use the @ char.'
        : null;
    },
),

In this instance, obscureText is set to true to hide the text, which is necessary for a password field.

In newer versions, errorMaxLines can be added directly to InputDecoration:

TextFormField(
  decoration: InputDecoration(
    errorMaxLines: 2,
  ),
  validator: (value) {
    if (value.isEmpty) {
      return 'Please Enter Something';
    }
    return null;
  },
)