dynamic input validation demo.

input_demo.dart

SizedBox(
  height: 200,
  child: Form(
    key: _formKey,
    child: TextFormField(
      controller: _ec,
      maxLines: null,
      expands: false,
      onChanged: (value) {
        // Trigger immediate validation on text change
        if (_formKey.currentState != null &&
            value.isNotEmpty) {
          _formKey.currentState!.validate();
        }
      },
      validator: (text) {
        if (text == null || text.isEmpty) {
          return 'Text is empty';
        }
        return null;
      },
      onEditingComplete: () {},
      decoration: InputDecoration(
        border: OutlineInputBorder(),
        labelText: 'Even Densed TextFiled',
        isCollapsed: true, // Added this
        contentPadding: EdgeInsets.all(12), // Added this
        prefixIcon: Icon(Icons.search),
        suffixIcon: IconButton(
          onPressed: () {
            if (_formKey.currentState?.validate() ??
                false) {
              // TODO submit
            }
          },
          icon: Icon(Icons.abc),
        ),
      ),
    ),
  ),
);