title: I have an error for import package in flutter
body: <p>Tips:</p>
  <p>(Sorry for mistakes. English isn't my native language)</p>
  <p>(I'm new in flutter)</p>
  <p>I have many errors in my flutter project. I think that's because of packages. when I write: <code>import 'package:flutter/material.dart';</code>, android studio draw a red line under it that means error and when I hold down the mouse pointer on import package, It says: <code>Target of URI doesn't exist: 'package:flutter/material.dart'</code> I think that's why all of the error. How can I fix it?</p>
  <p>My errors:</p>
  <pre><code>error: Target of URI doesn't exist: 'package:flutter/material.dart'. (uri_does_not_exist at [untitled6] bin\main.dart:1)
  
  error: The function 'runApp' isn't defined. (undefined_function at [untitled6] bin\main.dart:3)
  
  error: Classes can only extend other classes. (extends_non_class at [untitled6] bin\main.dart:5)
  
  error: Undefined class 'Widget'. (undefined_class at [untitled6] bin\main.dart:8)
  
  error: Undefined class 'BuildContext'. (undefined_class at [untitled6] bin\main.dart:8)
  
  error: The method 'MaterialApp' isn't defined for the type 'MyApp'. (undefined_method at [untitled6] bin\main.dart:9)
  
  error: Classes can only extend other classes. (extends_non_class at [untitled6] bin\main.dart:16)
  
  error: Undefined class 'Widget'. (undefined_class at [untitled6] bin\main.dart:19)
  
  error: Undefined class 'BuildContext'. (undefined_class at [untitled6] bin\main.dart:19)
  
  error: The method 'Material' isn't defined for the type 'MyScaffold'. (undefined_method at [untitled6] bin\main.dart:20)
  
  error: The method 'Column' isn't defined for the type 'MyScaffold'. (undefined_method at [untitled6] bin\main.dart:21)
  
  error: The name 'Widget' isn't a type so it can't be used as a type argument. (non_type_as_type_argument at [untitled6] bin\main.dart:22)
  
  error: The name 'Row' isn't a class. (creation_with_non_type at [untitled6]     bin\main.dart:23)
  
  error: The name 'IconButton' isn't a class. (creation_with_non_type at [untitled6] bin\main.dart:24)
  
  error: The method 'Icon' isn't defined for the type 'MyScaffold'. (undefined_method at [untitled6] bin\main.dart:25)
  
  error: Undefined name 'Icons'. (undefined_identifier at [untitled6] bin\main.dart:25)
  
  error: The name 'Text' isn't a class. (creation_with_non_type at [untitled6] bin\main.dart:29)
  
  error: The name 'IconButton' isn't a class. (creation_with_non_type at [untitled6] bin\main.dart:30)
  
  error: The method 'Icon' isn't defined for the type 'MyScaffold'. (undefined_method at [untitled6] bin\main.dart:32)
  
  error: Undefined name 'Icons'. (undefined_identifier at [untitled6] bin\main.dart:32)
  
  error: Expected to find ')'. (expected_token at [untitled6] bin\main.dart:37)
  
  error: Expected to find ']'. (expected_token at [untitled6] bin\main.dart:38)
  
  error: Expected to find ')'. (expected_token at [untitled6] bin\main.dart:38)
  
  error: Expected to find ')'. (expected_token at [untitled6] bin\main.dart:39)
  
  info: The method doesn't override an inherited method. (override_on_non_overriding_member at [untitled6] bin\main.dart:8)
  
  info: Unnecessary new keyword. (unnecessary_new at [untitled6] bin\main.dart:11)
  
  info: The method doesn't override an inherited method. (override_on_non_overriding_member at [untitled6] bin\main.dart:19)
  
  info: Unnecessary new keyword. (unnecessary_new at [untitled6] bin\main.dart:23)
  
  info: Unnecessary new keyword. (unnecessary_new at [untitled6] bin\main.dart:24)
  
  info: Unnecessary new keyword. (unnecessary_new at [untitled6] bin\main.dart:29)
  
  info: Unnecessary new keyword. (unnecessary_new at [untitled6] bin\main.dart:30)
  </code></pre>
  <p>Could you please help me? My work has been delayed for a few days</p>