Android Studio：如果您在AndroidManifest.xml中声明了此活动，则无法找到显式活动类

Question

我的代码清单是：我收到运行时异常“无法找到显式类”，是否已在AndroidManifest.xml中声明了此活动？

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.awesomeapps.yash.messagescheduler"
    android:installLocation="auto">




    <uses-permission android:name="android.permission.SEND_SMS"></uses-permission>

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

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".CancelAnAlarmActivity"
            android:label="Cancel Alarm">
        </activity>
    <service android:name="com.awesomeapps.yash.messagescheduler.SendSMSAlarmService"/>
    </application>
</manifest>