Android Widget：无法实例化活动 ComponentInfo，java.lang.ClassCastException

Question

我正在尝试制作一个小部件，它每分钟都会更改文本，但我正在努力让事情正常进行。我在标题中收到错误。

日志文件：

10-25 12:22:54.290: E/AndroidRuntime(21988): FATAL EXCEPTION: main
10-25 12:22:54.290: E/AndroidRuntime(21988): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.simpletext/com.example.simpletext.MainActivity}: java.lang.ClassCastException: com.example.simpletext.MainActivity cannot be cast to android.app.Activity
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2034)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread.access$700(ActivityThread.java:140)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.os.Handler.dispatchMessage(Handler.java:99)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.os.Looper.loop(Looper.java:137)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread.main(ActivityThread.java:4921)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at java.lang.reflect.Method.invokeNative(Native Method)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at java.lang.reflect.Method.invoke(Method.java:511)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at dalvik.system.NativeStart.main(Native Method)
10-25 12:22:54.290: E/AndroidRuntime(21988): Caused by: java.lang.ClassCastException: com.example.simpletext.MainActivity cannot be cast to android.app.Activity
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
10-25 12:22:54.290: E/AndroidRuntime(21988):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2025)
10-25 12:22:54.290: E/AndroidRuntime(21988):    ... 11 more

清单：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.simpletext"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <receiver
            android:name="MyWidgetProvider"
            android:icon="@drawable/ic_launcher"
            android:label="Simple Text" >
            <intent-filter>
                <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
            </intent-filter>

            <meta-data
                android:name="android.appwidget.provider"
                android:resource="@xml/widget_info" />
        </receiver>

        <activity
            android:name="com.example.simpletext.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

还有 MainActivity 类，我试图每 60 秒更新一次小部件（是因为我没有任何 onRecive 方法吗？-我在 Updejt.class 中设置布局，这就是我假设我不这样做的原因'不需要）：

package com.example.simpletext;

import java.util.Timer;

import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;

public class MainActivity extends AppWidgetProvider{

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager,
            int[] appWidgetIds) {
        // TODO Auto-generated method stub
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new UpdejtText(context, appWidgetManager), 1, 60000);

        super.onUpdate(context, appWidgetManager, appWidgetIds);
    }

}

UpdejtText 类：

package com.example.simpletext;

import java.util.TimerTask;

import android.appwidget.AppWidgetManager;
import android.content.ComponentName;
import android.content.Context;
import android.widget.RemoteViews;

public class UpdejtText extends TimerTask{
    RemoteViews remoteViews;
    AppWidgetManager appWidgetManager;
    ComponentName thisWidget;
    value = 0;

public UpdejtText(Context context, AppWidgetManager appWidgetManager) {

    this.appWidgetManager = appWidgetManager;
    remoteViews = new RemoteViews(context.getPackageName(), R.layout.activity_main);
    thisWidget = new ComponentName(context, UpdejtText.class);
    value= someValue();
}

@Override
public void run(){
    remoteViews.setTextViewText(R.id.textView1, Pomagac.getText1(value));
    remoteViews.setTextViewText(R.id.textView2, Pomagac.getText2(value));
    appWidgetManager.updateAppWidget(thisWidget, remoteViews);
}

}

帮助表示赞赏！

Answer 1

这是因为您的 MainActivity 没有扩展 Activity 类。 相反，它扩展了 AppWidgetProvider，

MainActivity extends AppWidgetProvider

检查此链接以在清单中为小部件注册您的课程，

http://www.vogella.com/articles/AndroidWidgets/article.html

Answer 2

MainActivity 是 AppWidgetProvider 类型，但是在您的班级中的某个地方，您将其类型转换为普通的 Android Activity 所以您得到的是 classcastException..

Answer 3

你不需要任何Activity 来处理小部件。所以你可以删除它。

只需将MainActivity.java 替换为MyWidgetProvider.java

    package com.example.simpletext;

import java.util.Timer;

import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.Context;

public class MyWidgetProvider extends AppWidgetProvider{

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager,
            int[] appWidgetIds) {
        // TODO Auto-generated method stub
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new UpdejtText(context, appWidgetManager), 1, 60000);

        super.onUpdate(context, appWidgetManager, appWidgetIds);
    }

}

并使用此清单文件

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.simpletext"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <receiver
            android:name=".MyWidgetProvider"
            android:icon="@drawable/ic_launcher"
            android:label="Simple Text" >
            <intent-filter>
                <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
            </intent-filter>

            <meta-data
                android:name="android.appwidget.provider"
                android:resource="@xml/widget_info" />
        </receiver>

    </application>

</manifest>

注意： 要添加小部件，请长按主屏幕并添加您想要的小部件。

希望对你有帮助！！