java - 从线程返回字符串 Android Java

Question

我正在使用线程执行 HttpURLConnection 并从数据库中获取数据。下面的代码代表了我想要完成的任务，但我收到了一个错误

str_Data = "John Doe";

错误:从内部类中访问变量“str_Data”

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.MainActivity);

    String str_Name = "";

    str_Name = setDataToText(str_Url);

}

 private String setDataToText(String urlStr) {
    final String url = urlStr;
    String str_Data = "";

    new Thread() {
        public void run() {
            //A code to retrieve data is executed
            //Data is Converted and added to the string str_Data;
            str_Data = "John Doe";
        }
    }
    return str_Data;
}

我想将 new Thread() 上的 run() 操作中的 str_Data 值设置为从数据库恢复的数据。

编辑: 这就是我解决问题的方法，如果使用此方法时这不是一个好的做法，请告诉我，感谢您的帮助:

String str_Data = "";

public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.MainActivity);

setDataToText(str_Url);
txtName.setText(str_Data);
}

private void setDataToText(String urlStr) {
    new Thread(new Runnable() {
    @Override
        public void run() {
        // TODO Auto-generated method stub
        //A code to retrieve data is executed
        //Data is Converted and added to the string str_Data;
        str_Data = "John Doe";
        }
    }).start();
}

Answer 1

正确的方法是使用 Callable 和 Future 接口(interface)。

public static void main(String[] args) throws ExecutionException, InterruptedException {
   ExecutorService executorService = Executors.newSingleThreadExecutor();
   CallableClass callableClass = new CallableClass();
   Future<String> future = executorService.submit(callableClass);

   String name = future.get();
   System.out.println(name);
}

public class CallableClass implements Callable<String> {

    @Override
    public String call() throws Exception {
       return "John Doe";
    }
}