java Android Studio MainActivity即使在新项目上也不存在

Question

我发布了一个关于我在安卓 studio中收到的空指针的问题，该指针与始终为空的上下文有关。此外，无论我如何分配它，这个错误都会不断出现

我一直无法找到这个问题的解决方案，所以决定开始一个全新的项目——不写一行代码，我也会遇到同样的错误

控制台错误

$ adb shell am start -n "za.co.freelanceweb.scheduler/za.co.freelanceweb.scheduler.MainActivity" -a 安卓.intent.action.MAIN -c 安卓.intent.category.LAUNCHER
Error while executing: am start -n "za.co.freelanceweb.scheduler/za.co.freelanceweb.scheduler.MainActivity" -a 安卓.intent.action.MAIN -c 安卓.intent.category.LAUNCHER
Starting: Intent { act=安卓.intent.action.MAIN cat=[安卓.intent.category.LAUNCHER] cmp=za.co.freelanceweb.scheduler/.MainActivity }
Error type 3
Error: Activity class {za.co.freelanceweb.scheduler/za.co.freelanceweb.scheduler.MainActivity} does not exist.

Error while Launching activity

AndroidManifest。xml（未触及）

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
    package="za.co.freelanceweb.scheduler">

    <application
        安卓:allowBackup="true"
        安卓:icon="@mipmap/ic_launcher"
        安卓:label="@string/app_name"
        安卓:roundIcon="@mipmap/ic_launcher_round"
        安卓:supportsRtl="true"
        安卓:theme="@style/AppTheme">
        <activity 安卓:name=".MainActivity">
            <intent-filter>
                <action 安卓:name="安卓.intent.action.MAIN" />

                <category 安卓:name="安卓.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

gradle项目文件（未触及）

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

buildscript {
    repositories {
        google()
        jcenter()

    }
    dependencies {
        classpath 'com.安卓.tools.build:gradle:3.5.0'

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

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

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

gradle应用程序文件（未触及）

apply plugin: 'com.安卓.application'

安卓 {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "za.co.freelanceweb.scheduler"
        minSdkVersion 21
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "安卓x.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-安卓-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation '安卓x.appcompat:appcompat:1.1.0'
    implementation '安卓x.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    安卓TestImplementation '安卓x.test:runner:1.2.0'
    安卓TestImplementation '安卓x.test.espresso:espresso-core:3.2.0'
}

主要活动。java（未触及）

package za.co.freelanceweb.scheduler;

import 安卓x.appcompat.app.AppCompatActivity;

import 安卓.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

Answer 1

Delete this Three folder and restart android Studio . Doing this will not delete your old project. But don't delete the Android Studio project folder