为什么我会收到错误:在R类中找不到符号变量

以下源代码应制作图片并在屏幕上显示.但我得到一些错误.Cannot resolve symbol 'activity_fullscreen',同样为imageView1,dummy_button,fullscreen_content和fullscreen_content_controls.

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fullscreen);

        mVisible = true;
        mControlsView = findViewById(R.id.fullscreen_content_controls);
        mContentView = findViewById(R.id.fullscreen_content);


        // Set up the user interaction to manually show or hide the system UI.
        mContentView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                toggle();
            }
        });

        // Upon interacting with UI controls, delay any scheduled hide()
        // operations to prevent the jarring behavior of controls going away
        // while interacting with the UI.
        findViewById(R.id.dummy_button).setOnTouchListener(mDelayHideTouchListener);//dummy abaendern


        //super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_fullscreen);
        this.imageView = (ImageView)this.findViewById(R.id.imageView1);
        Button photoButton = (Button) this.findViewById(R.id.dummy_button);
        photoButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent cameraIntent = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(cameraIntent, CAMERA_REQUEST);
            }
        });


    }

那是我的进口:

import android.annotation.SuppressLint;
import android.app.Activity;
import android.graphics.Bitmap;
import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.os.Handler;
import android.view.MotionEvent;
import android.view.View;
import android.content.Intent;
import android.widget.Button;
import android.widget.ImageView;
import android.R;

现在让我们来看看activity_fullscreen.xml缺少的部分肯定在那里.

我已经检查了以下答案中的建议.据我所知,名称不包含任何非法字符.我也已经通过File - > Invalidate Caches/Restart重新启动了android studio.

但我仍然没有找到解决问题的方法.如何解决R而不是其内容是否可行？欢迎任何想法.谢谢

你导入了错误的'R'

删除这个:

import android.R;

添加这个:

import com.yourCompany.yourApp.R;