如何从另一个类运行方法?人造人

Question

基本上我想从另一个类调用一个方法。我希望在MainActivity.java中调用DownloadXML.java中的data()方法

这是一个安卓应用程序

所以这里是主要活动.java

public class MainActivity extends ListActivity {
    String item;       
    DownloadXML a = new DownloadXML();
    a.data(); 
    // SYNTAX ERROR ON TOKEN "DATA" IDENTIFIER EXPECTED AFTER THIS TOKEN
   @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        try{
            item = getItemFromXML(this);
        }catch (XmlPullParserException e){
        }catch (IOException e){
        }
        String[] items = item.split("n");
        setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, items));
    }
    public String getItemFromXML(Activity activity) throws XmlPullParserException, IOException{
        StringBuffer stringBuffer = new StringBuffer();
        Resources res = activity.getResources();
        XmlResourceParser xpp = res.getXml(R.xml.items);
        xpp.next();
        int eventType = xpp.getEventType();
        while (eventType != XmlPullParser.END_DOCUMENT){
            if (eventType == XmlPullParser.START_TAG){
                if (xpp.getName().equals("Item")){
                    stringBuffer.append(xpp.getAttributeValue(null, "Event") + "n");
                }
                if (xpp.getName().equals("ab")){
                    stringBuffer.append(xpp.getAttributeValue(null, "when") + "n");
                }
                if (xpp.getName().equals("cd")){
                    stringBuffer.append(xpp.getAttributeValue(null, "where") + "n" + "----------------------------------------------" + "n");
                }

            }
            eventType = xpp.next();
        }
        return stringBuffer.toString();
    }
}

这是下载XML

.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.net.URL;
public class DownloadXML {
    DownloadXML(){
    }
    public void data() throws Exception{
        URL url = new URL("http://localhost:8080/lab/lab.xml");
          BufferedReader reader = new BufferedReader
          (new InputStreamReader(url.openStream()));
          BufferedWriter writer = new BufferedWriter
          (new FileWriter("C:\Users\eyas\workspace\CebuHQ\res\xml\items.xml"));
          String line;
          while ((line = reader.readLine()) != null) {
             System.out.println(line);
             writer.write(line);
             writer.newLine();
          }
          reader.close();
          writer.close();
    }
}

当我尝试实例化它并调用该方法时，它的错误为：

DownloadXML a = new DownloadXML();
a.data(); SYNTAX ERROR ON TOKEN "DATA" IDENTIFIER EXPECTED AFTER THIS TOKEN

你们能帮我这个吗？谢谢

Answer 1

唯一可以超出方法的代码是变量声明和初始化。如果要调用方法，则必须在方法或构造函数中执行此操作。

public class MainActivity extends ListActivity {
    String item;
    DownloadXML a = new DownloadXML();
    a.data(); //This won't work. Put it inside a method
   @Override
    protected void onCreate(Bundle savedInstanceState) {
        //...
    }

请尝试这样的事情：

    public class MainActivity extends ListActivity {
            String item; 
           @Override
            protected void onCreate(Bundle savedInstanceState) {
                //...
                DownloadXML a = new DownloadXML();
                a.data(); 
            }
}

Answer 2

试试这个：

 public class DownloadXML {
     public static void data(){
        // Do whatever you want
     }
 }

并像这样称呼它：

 DownloadXML.data();

Answer 3

为了调用另一个包的类，你需要相对地编码到每个包的意图中。此线程描述了如何完成此操作的总体任务。本质上，一个包必须愿意接受另一个包为其标记的任何内容。您还应该查找进程间通信。这是因为Android使用了Java的"沙盒"概念。我希望我正确理解了你的问题...