java - 读取 XML 时出错

Question

我正在为 Android 创建一个应用程序，它包括读取 XML 文件，将 XML 中的一些数据添加到放入 Spinner 的 ArrayList 中。 这是代码:

package com.rezoluz.fsx_pocket;

import java.util.ArrayList;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;

import android.os.Environment;

public class Scanner extends Main {

    public ArrayList<String> getCategorys() throws XmlPullParserException, IOException {
        ArrayList<String> categorys = new ArrayList<String>();
        categorys.add("Please select a category");
        //START ADDING HERE
        XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
        factory.setNamespaceAware(true);
        XmlPullParser parser = factory.newPullParser();
        File file = new File(Environment.getExternalStorageDirectory()+ "/fsx_kneeboard/categories.xml");
        FileInputStream fis = new FileInputStream(file);
        parser.setInput(new InputStreamReader(fis));
        parser.next();
        int eventType = parser.getEventType();
        int Categories = 0;
        while (eventType != XmlPullParser.END_DOCUMENT) {
            if (eventType == XmlPullParser.START_TAG && parser.getName().equals("categories")) {
                Categories++;
            } if (eventType == XmlPullParser.START_TAG && parser.getName().equals("category") && Categories == 1) {
                Categories++;
            } if (eventType == XmlPullParser.START_TAG && parser.getName().equals("name") && Categories == 2) {
                categorys.add(parser.getText());
            }
            parser.next();
        }
        return categorys;

    }
}

这是在另一个类中(Shortcuts.java):

public boolean launched = false;

Scanner scanner = new Scanner();
ArrayList<String> items;
        try {
            items = scanner.getCategorys();
        } catch (FileNotFoundException e) {
            items = null;
            e.printStackTrace();
        } catch (XmlPullParserException e) {
            items = null;
            e.printStackTrace();
        } catch (IOException e) {
            items = null;
            e.printStackTrace();
        }
        @SuppressWarnings({ "unchecked", "rawtypes" })
        ArrayAdapter<CharSequence> adapter = new ArrayAdapter(this,android.R.layout.simple_spinner_item, items);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        selection.setAdapter(adapter);

        selection.setOnItemSelectedListener(new OnItemSelectedListener() {

            public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
                    long arg3) {
                final String simulatorCommands = getString(R.string.Simulator_Commands); //Setting Shortcuts
                final String controlSurfaceCommands = getString(R.string.Control_Surface_Commands);
                TextView Text = (TextView)findViewById(R.id.shortcutsText);  //Defining the TextView
                Spinner selection = (Spinner) findViewById(R.id.shortcutsSpinner); //Defining the Spinner
                String selText = selection.getSelectedItem().toString(); //Finding the text of the selected item, from the Spinner
                //Setting the TextView to X. START
                int selected = selection.getSelectedItemPosition();
                if (selected==0 && launched==true) {
                    selection.setSelection(prevSelection);
                    Context context = getApplicationContext();
                    final String featureToast = getString(R.string.shortcuts_notValid);
                    CharSequence text = featureToast;
                    int duration = Toast.LENGTH_SHORT;

                    Toast toast = Toast.makeText(context, text, duration);
                    toast.show();
                }
                launched = true;
                if (selection.getSelectedItemPosition()!=0) {
                        prevSelection = selection.getSelectedItemPosition();
                }
                if (selText.equals("Please select a category")) {
                    Text.setText(Html.fromHtml("Please select a category from the list above."));
                }
                if (selText.equals("Simulator Commands")) {
                    Text.setText(Html.fromHtml(simulatorCommands));
                }
                if (selText.equals("Control Surface Commands")) {
                    Text.setText(Html.fromHtml(controlSurfaceCommands));
                }
                //END

            }

我已将代码缩减为我认为必要的部分。当我打开快捷方式类时，它强制关闭。 这是日志猫:

> 03-31 17:53:12.340: D/AndroidRuntime(6625): Shutting down VM 03-31
> 17:53:12.340: W/dalvikvm(6625): threadid=1: thread exiting with
> uncaught exception (group=0x4001d7e8) 03-31 17:53:12.385:
> E/AndroidRuntime(6625): FATAL EXCEPTION: main 03-31 17:53:12.385:
> E/AndroidRuntime(6625): java.lang.RuntimeException: Unable to start
> activity
> ComponentInfo{com.rezoluz.fsx_pocket/com.rezoluz.fsx_pocket.Shortcuts}:
> java.lang.NullPointerException 03-31 17:53:12.385:
> E/AndroidRuntime(6625):   at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> android.app.ActivityThread.access$2300(ActivityThread.java:125) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> android.os.Handler.dispatchMessage(Handler.java:99) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> android.os.Looper.loop(Looper.java:123) 03-31 17:53:12.385:
> E/AndroidRuntime(6625):   at
> android.app.ActivityThread.main(ActivityThread.java:4627) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> java.lang.reflect.Method.invokeNative(Native Method) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> java.lang.reflect.Method.invoke(Method.java:521) 03-31 17:53:12.385:
> E/AndroidRuntime(6625):   at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> dalvik.system.NativeStart.main(Native Method) 03-31 17:53:12.385:
> E/AndroidRuntime(6625): Caused by: java.lang.NullPointerException
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> com.rezoluz.fsx_pocket.Scanner.getCategorys(Scanner.java:31) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> com.rezoluz.fsx_pocket.Shortcuts.onCreate(Shortcuts.java:78) 03-31
> 17:53:12.385: E/AndroidRuntime(6625):     at
> android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
> 03-31 17:53:12.385: E/AndroidRuntime(6625):   ... 11 more

这是它尝试读取的 XML 文件:

<?xml version='1.0' encoding='UTF-8' standalone='yes' ?>
<categories>
  <category>
    <name>Simulator Commands</name>
    <id>1</id>
  </category>
  <category>
    <name>Control Surface Commands</name>
    <id>2</id>
  </category>
  <category>
    <name>Control Surface Commands</name>
    <id>3</id>
  </category>
  <category>
    <name>General Aircraft Commands</name>
    <id>4</id>
  </category>
  <category>
    <name>Light Commands</name>
    <id>5</id>
  </category>
  <category>
    <name>Radio Commands</name>
    <id>6</id>
  </category>
  <category>
    <name>Autopilot Commands</name>
    <id>7</id>
  </category>
  <category>
    <name>Intrument Commands</name>
    <id>8</id>
  </category>
  <category>
    <name>View Commands</name>
    <id>9</id>
  </category>
  <category>
    <name>Slew Keys</name>
    <id>10</id>
  </category>
  <category>
    <name>Mission Commands</name>
    <id>11</id>
  </category>
  <category>
    <name>Multiplayer Commands</name>
    <id>12</id>
  </category>
  <category>
    <name>C172 Intrument Panels</name>
    <id>13</id>
  </category>
  <category>
    <name>BE58 Intrument Panels</name>
    <id>14</id>
  </category>
</categories>

感谢您的宝贵时间和帮助。泽奥基拉

Answer 1

Scanner.java 中的第 31 行出现 NullPointerException:

E/AndroidRuntime(6625): Caused by: java.lang.NullPointerException
E/AndroidRuntime(6625): at com.rezoluz.fsx_pocket.Scanner.getCategorys(Scanner.java:31)