片段错误：类型不兼容，需要 android.app.fragment 但找到了 Activity.messagefragment

 @Override
public void onDrawerItemSelected(View view, int position) {
    displayView(position);
}

private void displayView(int position) {
    Fragment fragment = null;
    String title = getString(R.string.app_name);
    switch (position) {
        case 0:
            fragment = new HomeFragment();
            title = getString(R.string.title_home);
            break;
        case 1:
            fragment = new FriendsFragment();
            title = getString(R.string.title_friends);
            break;
        case 2:
            fragment = new MessageFragment();
            title = getString(R.string.title_messages);
            break;
        default:
            break;
    }

打印的错误是：

incompatible types,required android.app.fragment but found activity.messagefragment

In your messagefragment你需要导入的类

import android.app.Fragment;

代替

import android.support.v4.app.Fragment;