Android：无法加载 XML

Question

新的 Android Studio 项目

创建的资产文件夹

创建新活动的构造函数（项目中的第二个）以在调用活动时读取 XML。

将我要读取的xml文件放入我创建的assets文件夹中

这里是读取xml的代码

    AssetManager assetManager = getAssets();
    InputStream xmlFile= assetManager.open("menu.xml");

    // CREATE BUILDER FACTORY/BUILDER
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(xmlFile);

    //Element root = doc.getDocumentElement();
    //Log.d("root element",root.getNodeName());

    NodeList list = doc.getElementsByTagName("subcategory");

    Log.d("NODE", String.valueOf(list.getLength()));

运行应用程序时，调用按钮以调出新活动，但崩溃... 请帮忙

这里是 logcat 输出

07-28 15:52:30.138    6990-6990/com.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.app/com.app.MainMenu}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:130)
            at android.app.ActivityThread.main(ActivityThread.java:3691)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at android.content.ContextWrapper.getAssets(ContextWrapper.java:74)
            at com.app.MainMenu.<init>(MainMenu.java:60)
            at java.lang.Class.newInstanceImpl(Native Method)
            at java.lang.Class.newInstance(Class.java:1409)
            at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1565)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:130)
            at android.app.ActivityThread.main(ActivityThread.java:3691)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
            at dalvik.system.NativeStart.main(Native Method)

MainACtivity 是一个默认的 android studio 活动，带有一个按钮来调用新活动 MainMenu 是调用 XML 的第二个活动

请指教。

谢谢！

Answer 1

我认为您需要针对您的活动所在的任何上下文调用 getAssets()，

context.getAssets();