android - androidStudio中的“软件包android.support.v7.app不存在”错误

我只是开始使用androidStudio进行android开发
我正在遵循udacity教程，他们要求我们复制粘贴一些代码并运行它
粘贴后我无法操作鳕鱼
我认为主要问题是在导入时

import android.support.v7.app.AppCompatActivity;

我已经检查了互联网以解决此问题，包括stackoverflow
但似乎每种情况都不同
我试图进口
import androidx.appcompat.app.AppcompatActivity;
代替
import android.support.v7.app.AppCompatActivity;
但它没有晕倒
我正在使用androidStudio 3.4版

主要活动：

package com.example.android.justjava;

/**
 * IMPORTANT: Make sure you are using the correct package name.
 * This example uses the package name:
 * package com.example.android.justjava
 * If you get an error when copying this code into Android studio, update it to match teh package name found
 * in the project's AndroidManifest.xml file.
 **/


import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;

/**
 * This app displays an order form to order coffee.
 */
public class MainActivity extends AppCompatActivity {

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

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        display(1);
    }

    /**
     * This method displays the given quantity value on the screen.
     */
    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }
}

module.App（构建gradle）：

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.1"
    defaultConfig {
        applicationId "com.example.android.justjava"
        minSdkVersion 15
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

error: cannot find symbol class AppcompatActivity
error: cannot find symbol class AppCompatActivity
error: method does not override or implement a method from a supertype
error: cannot find symbol variable super
error: cannot find symbol method setContentView(int)
error: cannot find symbol method findViewById(int)

最佳答案

您正在使用androidx库。

 implementation 'androidx.appcompat:appcompat:1.0.2'

然后，您将无法使用支持库类的导入。

它是right class：

import androidx.appcompat.app.AppCompatActivity;