广播接收器 Android

Question

如何解决这些问题？

请帮助我，它不断停止不起作用

（崩溃）

我使用的是 12.0 Api 31

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.4, PID: 23001
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.4/com.example.4.MainActivity}: java.lang.ClassCastException: com.example.4.MainActivity cannot be cast to android.app.Activity
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3549)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3796)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2214)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loopOnce(Looper.java:201)
        at android.os.Looper.loop(Looper.java:288)
        at android.app.ActivityThread.main(ActivityThread.java:7842)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
     Caused by: java.lang.ClassCastException: com.example.4.MainActivity cannot be cast to android.app.Activity
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1273)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3536)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3796) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:103) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2214) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loopOnce(Looper.java:201) 
        at android.os.Looper.loop(Looper.java:288) 
        at android.app.ActivityThread.main(ActivityThread.java:7842) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003) 

MainActivity.java：

package com.example.4;


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

public class MainActivity extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Intent Detected.", Toast.LENGTH_LONG).show();
    }
}

AndroidMainfest.xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.example.4">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.4">
        <activity
            android:name=".MainActivity"
            android:exported="true"
            tools:ignore="Instantiatable">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <receiver android:name="MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="com.tutorialspoint.CUSTOM_INTENT">
                </action>
            </intent-filter>

        </receiver>
    </application>

</manifest>

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:context=".MainActivity">

        <TextView
            android:id="@+id/textView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:text="Example of Broadcast"
            android:textSize="30dp" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_above="@+id/imageButton"
            android:layout_centerHorizontal="true"
            android:layout_marginBottom="40dp"
            android:text="Tutorials point "
            android:textColor="#ff87ff09"
            android:textSize="30dp" />

        <ImageButton
            android:id="@+id/imageButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:src="@drawable/su"
            tools:ignore="SpeakableTextPresentCheck" />

        <Button
            android:id="@+id/button2"
            android:layout_width="268dp"
            android:layout_height="145dp"
            android:layout_below="@+id/imageButton"
            android:layout_centerHorizontal="true"
            android:onClick="broadcastIntent"
            android:text="Broadcast Intent" />

    </RelativeLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

无需阅读它，因为我不能发布我的帖子，因为它的大部分代码所以我正在写这个原因我希望我能解决我的问题这是我屏幕上的第五个小时

Answer 1

java.lang.ClassCastException: com.example.4.MainActivity 无法转换为 android.app.Activity

该异常告诉您MainActivity 不是Activity 类的有效子级，而是BroadcastReceiver 或Service。查看Manifest.xml，您有2 个同名的类。一个用于真正的活动，另一个用于您称为MainActivity 的服务。 MainActivity 是一个扩展 Activity 或 AppCompatActivity 的类。我建议您为BroadcastReceiver 使用更好的名称。像这样的：

public class Receiver extends BroadcastReceiver {

Manifest.xml 看起来像这样：

<receiver android:name="Receiver"
    android:exported="true">
        <intent-filter>
            <action android:name="com.tutorialspoint.CUSTOM_INTENT> 
           </action>
        </intent-filter>
</receiver>

您仍然需要找到您正在使用的真实主要活动，并确保它与Manifest.xml 中的相同，在本例中为MainActivity。

<activity
    android:name=".MainActivity"
    android:exported="true"
    tools:ignore="Instantiatable">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
</activity>