java - 无法解析Android Studio中的Symbol v7和appComapat Activity导入

Question

我在这个问题上停留了3-4天，并且尝试了所有可能的事情，清除了缓存，清理了项目，但仍然无法在设备上运行。弹出错误，显示无法解决v7.app.appcompatActivity。感谢您的帮助，代码如下:
包com.edunomics.flashchatnewfirebase;

import android.os.Bundle;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;
import android.support.v7.app.AppcompatActivity;
import androidx.appcompat.app.AppCompatActivity;


public class MainChatActivity extends AppCompatActivity {

    // TODO: Add member variables here:
    private String mDisplayName;
    private ListView mChatListView;
    private EditText mInputText;
    private ImageButton mSendButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_chat);

        // TODO: Set up the display name and get the Firebase reference


        // Link the Views in the layout to the Java code
        mInputText = (EditText) findViewById(R.id.messageInput);
        mSendButton = (ImageButton) findViewById(R.id.sendButton);
        mChatListView = (ListView) findViewById(R.id.chat_list_view);

        // TODO: Send the message when the "enter" button is pressed


        // TODO: Add an OnClickListener to the sendButton to send a message

    }

    // TODO: Retrieve the display name from the Shared Preferences


    private void sendMessage() {

        // TODO: Grab the text the user typed in and push the message to Firebase

    }

    // TODO: Override the onStart() lifecycle method. Setup the adapter here.


    @Override
    public void onStop() {
        super.onStop();

        // TODO: Remove the Firebase event listener on the adapter.

    }

}

这是我的app的build.gradle文件

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.6.3'
        classpath 'com.google.gms:google-services:4.3.3'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
        google()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

Answer 1

只需要一个import语句。请替换以下import语句

import android.support.v7.app.AppCompatActivity;

下面的 import语句。

import androidx.appcompat.app.AppCompatActivity;