Broadcast Receivers Android

Question

如何解决这些问题?

请帮助我，它一直停止不工作

(崩溃)

我正在使用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>

不需要读这个，因为我不能发布我的帖子，因为它的大部分代码，所以我写这个原因，我希望我能解决我的问题，这是我的屏幕上的第五个小时

Answer 1

java.lang。com.example.4 ClassCastException。MainActivity不能强制转换为android.app.Activity

该异常告诉您MainActivity不是Activity类的有效子类，而是BroadcastReceiver或Service。查看Manifest.xml，您有两个具有相同名称的类。一个用于真正的活动另一个用于服务你称之为MainActivity。MainActivity是扩展Activity或AppCompatActivity的类。我建议你给BroadcastReceiver取个更好的名字。像这样:

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>

你仍然需要找到真实的你正在使用的主要活动，并确保它有相同的Manifest.xml，在这种情况下，是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>