java.lang.RuntimeException: 无法实例化活动

Question

我正在尝试编写一个 Android 应用程序，当您单击一个按钮时它会记录它会将文本放入控制台，但是当我编译它并运行它时出现错误在我的 Galaxy S7 edge 运行ning 7.0 API 版本 24.

I've read that I need to add something into the manifest file 但是我不确定我需要添加什么。

FATAL EXCEPTION: main Process: me.adamstephenson.test.test1, PID: 16405 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{me.adamstephenson.test.test1/me.adamstephenson.test.test1.MainActivity}: java.lang.ClassCastException: me.adamstephenson.test.test1.MainActivity cannot be cast to android.app.Activity

package me.adamstephenson.test.test1;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity {
    public class MyActivity extends Activity {
        protected void onCreate(Bundle icicle) {
            super.onCreate(icicle);

            setContentView(R.layout.activity_main);

            final Button button = (Button) findViewById(R.id.RequestKey);
            button.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    Log.d("RequestKey", "Clicked");
                }
            });
        }
    }
}

Source

布局如下

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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="me.adamstephenson.test.test1.MainActivity">

<Button
    android:id="@+id/RequestKey"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Button"
    tools:layout_editor_absoluteX="196dp"
    tools:layout_editor_absoluteY="129dp" />
</android.support.constraint.ConstraintLayout>

清单文件终于来了

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="me.adamstephenson.test.test1">

<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/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

</manifest>

Answer 1

您在清单中引用了错误的 class。 MyActivity 是 Activity，而不是 MainActivity。将您的清单更改为以下内容：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="me.adamstephenson.test.test1">

    <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/AppTheme">
        <activity android:name=".MainActivity$MyActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

和

你也应该让你的内心 activity static :

public class MainActivity {
    public static class MyActivity extends Activity {
        ...
    }
}

Answer 2

因为您的 activity class 被创建为内部 class 和静态 class。我不知道你为什么选择这种方式，而你可以这样正确地使用它：

public class MyActivity extends Activity {

    protected void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        setContentView(R.layout.activity_main);

        final Button button = (Button) findViewById(R.id.RequestKey);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Log.d("RequestKey", "Clicked");
            }
        });
    }
    .
    .
    .
     // other methods or inner class can exist here
   }

java.lang.RuntimeException: 无法实例化活动

java.lang.RuntimeException: Unable to instantiate activit

java

android

manifest

runtimeexception