Android开发找不到main

setContentView(R.layout.main);

一直提示找不到main,我用的新版的，layout里面有两个xml文件，没有main.xml，各位遇到这问题了吗？
setContentView(R.layout.fragment_main);
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
 
        TextView username=(TextView)findViewById(R.id.username);
//        username.setText(Html.fromHtml("Hello,大家好，<font color=red>我是你们的新导师</font>"));
        
        
        String userText="你知道我的名字吗";
        SpannableStringBuilder style=new SpannableStringBuilder(userText);
        style.setSpan(new ForegroundColorSpan(Color.RED), 1, 3, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        username.setText(style);
        
        
        
        
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit();
        }
    }