Question

我在尝试按照本教程时遇到强制关闭错误：

http://www.bango29.com/go/blog/2011/android-asynctask-is-a-beauty-part-2

有什么建议吗？我真的不确定我在哪里出错了。

我的来源：

public class HttpGetAndroidExample {

    // The url of the website. This is just an example

    private static final String webSiteURL = "http://www.supercars.net/gallery/119513/2841/5.html";

    // The path of the folder that you want to save the images to

    private static final String folderPath = "<FOLDER PATH>";

    public static void main(String[] args) {

        try {

            // Connect to the website and get the html

            Document doc = Jsoup.connect(webSiteURL).get();

            // Get all elements with img tag ,

            Elements img = doc.getElementsByTag("img");

            for (Element el : img) {

                // for each element get the srs url
                String src = el.absUrl("src");

                System.out.println("Image Found!");

                System.out.println("src attribute is : " + src);

                getImages(src);

            }

        } catch (IOException ex) {

            System.err.println("There was an error");

            Logger.getLogger(HttpGetAndroidExample.class.getName()).log(Level.SEVERE,
                    null, ex);

        }

    }

    private static void getImages(String src) throws IOException {

        String folder = null;

        // Exctract the name of the image from the src attribute
        int indexname = src.lastIndexOf("/");

        if (indexname == src.length()) {

            src = src.substring(1, indexname);

        }

        indexname = src.lastIndexOf("/");

        String name = src.substring(indexname, src.length());

        System.out.println(name);

        // Open a URL Stream

        URL url = new URL(src);

        InputStream in = url.openStream();

        OutputStream out = new BufferedOutputStream(new FileOutputStream(
                folderPath + name));

        for (int b; (b = in.read()) != -1;) {

            out.write(b);

        }

        out.close();

        in.close();

    }

}

logcat的：

07-18 17:22:06.449: D/ActivityThread(11404): setTargetHeapUtilization:0.25
07-18 17:22:06.449: D/ActivityThread(11404): setTargetHeapIdealFree:8388608
07-18 17:22:06.449: D/ActivityThread(11404): setTargetHeapConcurrentStart:2097152
07-18 17:22:06.469: W/dalvikvm(11404): threadid=1: thread exiting with uncaught exception (group=0x41e1f438)
07-18 17:22:06.469: E/AndroidRuntime(11404): FATAL EXCEPTION: main
07-18 17:22:06.469: E/AndroidRuntime(11404): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.httpgetandroidexample/com.example.httpgetandroidexample.HttpGetAndroidExample}: java.lang.ClassCastException: com.example.httpgetandroidexample.HttpGetAndroidExample cannot be cast to android.app.Activity
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2012)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2113)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread.access$700(ActivityThread.java:139)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1224)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.os.Looper.loop(Looper.java:137)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread.main(ActivityThread.java:4918)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at java.lang.reflect.Method.invokeNative(Native Method)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at java.lang.reflect.Method.invoke(Method.java:511)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at dalvik.system.NativeStart.main(Native Method)
07-18 17:22:06.469: E/AndroidRuntime(11404): Caused by: java.lang.ClassCastException: com.example.httpgetandroidexample.HttpGetAndroidExample cannot be cast to android.app.Activity
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.Instrumentation.newActivity(Instrumentation.java:1068)
07-18 17:22:06.469: E/AndroidRuntime(11404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2003)
07-18 17:22:06.469: E/AndroidRuntime(11404):    ... 11 more

清单：

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="17" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.httpgetandroidexample.HttpGetAndroidExample"
            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>

  <uses-permission android:name="android.permission.INTERNET"></uses-permission>

</manifest>

Answer 1

有两个问题：

在清单中，您已将HttpGetAndroidExample类声明为活动。与此相反，HttpGetAndroidExample类不extend Activiy类。所以，它不是一项活动。这就是异常HttpGetAndroidExample cannot be cast to android.app.Activity的原因。将其扩展为Activity并创建所需的函数，或者如果它不是活动，则将其从清单中删除。

此外，教程链接上没有我可以看到这个课程的地方。

遵循ASyncTask示例时强制关闭

1 个答案: