java - 无法将示例 XML 文件导入/转换为字符串以进行解析

Question

我的问题更像是“我在这里做错了什么？”我正在尝试导入从 W3.schools 获得的示例 XML 文档。我试过 DOM 来获取一个可解析的文件，BufferStream(new FileBuilder(new File(xxx))) 将它变成一个字符串，然后偶然发现 XPullParser 试图将文档解析为工作元素。我已经完成了这个使用 maven 和 DOM，但 Android 似乎有点挑剔。我查看了整个 stackoverflow 和其他文档，但似乎找不到答案。

这是我得到的:

在MainActivity中初始化对象

    public void OnClickDisplayResults(View view) {
    final Button button = (Button) findViewById(R.id.button3);
    button.setOnClickListener(new View.OnClickListener() {
        public void onClick (View v) {

            TextView textView3 = (TextView) findViewById(R.id.textView3);
            textView3.setText(searchResults.initiateParsing(), TextView.BufferType.EDITABLE);
        }
    });
}

工厂

public String initiateParsing() {
    String result = "";
    XmlPullParserFactory pullParserFactory;
    try {
        pullParserFactory = XmlPullParserFactory.newInstance();
        XmlPullParser parser = pullParserFactory.newPullParser();

        InputStream in_s = getApplicationContext().getAssets().open("plant_catalog.xml");
        parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES, false);
        parser.setInput(in_s, null);

        parseXML(parser);

    } catch (XmlPullParserException e) {

        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return libInterface.getXmlResult();
}

private void parseXML(XmlPullParser parser) throws XmlPullParserException,IOException
{
    ArrayList<SearchResults> products = null;
    int eventType = parser.getEventType();
    SearchResults currentProduct = null;

    while (eventType != XmlPullParser.END_DOCUMENT){
        String name = null;
        switch (eventType){
            case XmlPullParser.START_DOCUMENT:
                products = new ArrayList();
                break;
            case XmlPullParser.START_TAG:
                name = parser.getName();
                if (name.equals("PLANT")){
                    currentProduct = new SearchResults();
                } else if (currentProduct != null){
                    if (name.equals("COMMON")){
                        currentProduct.name = parser.nextText();
                    } else if (name.equals("BOTANICAL")){
                        currentProduct.color = parser.nextText();
                    } else if (name.equals("PRICE")){
                        currentProduct.quantity= parser.nextText();
                    }
                }
                break;
            case XmlPullParser.END_TAG:
                name = parser.getName();
                try {
                    if (name.equalsIgnoreCase("PLANT") && currentProduct != null) {
                        products.add(currentProduct);
                    }
                }catch (Exception e) {
                    e.printStackTrace();
                }
        }
        eventType = parser.next();
    }

    printProducts(products);
}

private void printProducts(ArrayList<SearchResults> products)
{
    String content = "";
    Iterator<SearchResults> it = products.iterator();
    while(it.hasNext())
    {
        SearchResults currProduct  = it.next();
        content = content + "nnnProduct :" +  currProduct.name + "n";
        content = content + "Quantity :" +  currProduct.quantity + "n";
        content = content + "Color :" +  currProduct.color + "n";

    }
    libInterface.setXmlResult(content);
}

堆栈跟踪

Process: com.example.myapp, PID: 7441
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a  null object reference
at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:105)
at com.app.StateLibraryApplication.SearchResults.initiateParsing(SearchResults.java:48)
at com.app.StateLibraryApplication.MyActivity$3.onClick(MyActivity.java:54)
at android.view.View.performClick(View.java:4756)
at android.view.View$PerformClick.run(View.java:19749)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5256)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
02-22 13:00:24.527    7441-7441/com.example.myapp I/Process﹕ Sending signal. PID: 7441 SIG: 9

Answer 1

这就是我解决自己问题的方法

我阅读了 Context。

上下文是引发大部分错误的原因。

您必须将方法更改为:

 public String initiateParsing(Context context) {
    String result = "";
   FileInputStream fis = null;
    XmlPullParserFactory pullParserFactory;



    try {
        pullParserFactory = XmlPullParserFactory.newInstance();
        XmlPullParser parser = pullParserFactory.newPullParser();

        // uses Context to getApplicationContext().getResources();
        Resources res = context.getApplicationContext().getResources();

        // Use direct Resource Tag with R
        InputStream in_st = res.openRawResource(R.raw.plant_catalog);
        parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES, false);
        parser.setInput(in_st, null);

        parseXML(parser); // and so forth.....

主要是方法:thisIsMyMethod(Context context) { context.SOMETHING }

希望这可以为其他人节省 6 小时的研究时间。