Java Android：即使我在AndroidManifest.xml中定义了显式活动类，也找不到它？

我正在编写一个简单的应用程序，在应用程序启动5秒后触发一个警报，其中启动了另一个活动（AlarmDialog）。但是，当我运行我的应用程序时，出现以下错误：

原因：android.content.ActivityNotFoundException:无法找到 显式活动类{com.example.basicalarmsetter/AlarmDialog}； 您是否在AndroidManifest.xml中声明了此活动

考虑到我相信我已经在我的AndroidManifest.xml文件中声明了活动，这似乎有些奇怪：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.basicalarmsetter">

    <uses-permission android:name="com.android.alarm.permission.SET_ALARM" />

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

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

        <activity
            android:name=".AlarmDialog"
            android:label="@string/app_name"
            android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        </activity>

        <receiver android:name=".AlarmReceiver"/>
    </application>

</manifest>

package com.example.basicalarmsetter;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends Activity {
    private Context context;

    private AlarmManager alarmMgr;
    private PendingIntent alarmIntent;

    // Creates the Pending Intent used to set off the alarm
    private PendingIntent generateAlarmPendingIntent(Context context) {
        Intent intent = new Intent(context, AlarmReceiver.class);

        // Each alarm requires a unique id
        int alarmId = (int) (Math.random() * (10000 - 1 + 1) + 1);
        System.out.println("alarmId = " + alarmId);

        PendingIntent alarmPendingIntent = PendingIntent.getBroadcast(context, alarmId, intent, 0);
        return alarmPendingIntent;
    }

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

        context = getApplicationContext();

        // Set an alarm 5 seconds after now
        alarmMgr = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);

        alarmMgr.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 5000,
                generateAlarmPendingIntent(context));
    }
}

package com.example.basicalarmsetter;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context k1, Intent k2) {
        System.out.println("Alarm received!");

        Intent i = new Intent();
        i.setClassName("com.example.basicalarmsetter", "AlarmDialog");
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        k1.startActivity(i);
    }
}

package com.example.basicalarmsetter;

import android.app.Activity;
import android.os.Bundle;

public class AlarmDialog extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.alarm_dialog);
    }
}

报警接收器：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.basicalarmsetter">

    <uses-permission android:name="com.android.alarm.permission.SET_ALARM" />

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

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

        <activity
            android:name=".AlarmDialog"
            android:label="@string/app_name"
            android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        </activity>

        <receiver android:name=".AlarmReceiver"/>
    </application>

</manifest>

package com.example.basicalarmsetter;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends Activity {
    private Context context;

    private AlarmManager alarmMgr;
    private PendingIntent alarmIntent;

    // Creates the Pending Intent used to set off the alarm
    private PendingIntent generateAlarmPendingIntent(Context context) {
        Intent intent = new Intent(context, AlarmReceiver.class);

        // Each alarm requires a unique id
        int alarmId = (int) (Math.random() * (10000 - 1 + 1) + 1);
        System.out.println("alarmId = " + alarmId);

        PendingIntent alarmPendingIntent = PendingIntent.getBroadcast(context, alarmId, intent, 0);
        return alarmPendingIntent;
    }

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

        context = getApplicationContext();

        // Set an alarm 5 seconds after now
        alarmMgr = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);

        alarmMgr.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 5000,
                generateAlarmPendingIntent(context));
    }
}

package com.example.basicalarmsetter;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context k1, Intent k2) {
        System.out.println("Alarm received!");

        Intent i = new Intent();
        i.setClassName("com.example.basicalarmsetter", "AlarmDialog");
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        k1.startActivity(i);
    }
}

package com.example.basicalarmsetter;

import android.app.Activity;
import android.os.Bundle;

public class AlarmDialog extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.alarm_dialog);
    }
}

报警对话框：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.basicalarmsetter">

    <uses-permission android:name="com.android.alarm.permission.SET_ALARM" />

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

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

        <activity
            android:name=".AlarmDialog"
            android:label="@string/app_name"
            android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        </activity>

        <receiver android:name=".AlarmReceiver"/>
    </application>

</manifest>

package com.example.basicalarmsetter;

import android.app.Activity;
import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends Activity {
    private Context context;

    private AlarmManager alarmMgr;
    private PendingIntent alarmIntent;

    // Creates the Pending Intent used to set off the alarm
    private PendingIntent generateAlarmPendingIntent(Context context) {
        Intent intent = new Intent(context, AlarmReceiver.class);

        // Each alarm requires a unique id
        int alarmId = (int) (Math.random() * (10000 - 1 + 1) + 1);
        System.out.println("alarmId = " + alarmId);

        PendingIntent alarmPendingIntent = PendingIntent.getBroadcast(context, alarmId, intent, 0);
        return alarmPendingIntent;
    }

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

        context = getApplicationContext();

        // Set an alarm 5 seconds after now
        alarmMgr = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);

        alarmMgr.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 5000,
                generateAlarmPendingIntent(context));
    }
}

package com.example.basicalarmsetter;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context k1, Intent k2) {
        System.out.println("Alarm received!");

        Intent i = new Intent();
        i.setClassName("com.example.basicalarmsetter", "AlarmDialog");
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        k1.startActivity(i);
    }
}

package com.example.basicalarmsetter;

import android.app.Activity;
import android.os.Bundle;

public class AlarmDialog extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.alarm_dialog);
    }
}

文件结构：所有类

main活动

、

AlarmDialog

和

AlarmReceiver

都位于同一目录下。

替换：

Intent i=newintent（）；
i、 setClassName（“com.example.basicalarmsetter”、“AlarmDialog”）；

与：

Intent i=新的Intent（k1，AlarmDialog.class）；

---

这将使用更好的构造函数，有助于避免硬编码字符串中的错误。另外，如果您使用IDE重命名

AlertDialog

类，您的

意图也将被修改。
谢谢，这非常有效。