内部类可以访问但不能更新值 - AsyncTask

Question

我正在尝试使用Android解压缩文件夹AsyncTask.该类(称为Decompress)是一个内部类,Unzip其中Unzip本身是一个非Activity类.伪代码是:

public class Unzip {  
  private String index;  
  private String unzipDest;    //destination file for storing folder.
  private Activity activity;
  private boolean result;      //result of decompress.

  public void unzip(String loc) {

    Decompress workThread = new Decompress(loc, activity);
    workThread.execute();  
    if(unzip operation was successful) {
      display(index);
  }

  //Class Decompress:
class Decompress extends AsyncTask<Void, Integer, Boolean> {

        private ProgressDialog pd = null;
        private Context mContext;
                private String loc;
        private int nEntries;
        private int entriesUnzipped;

        public Decompress(String location, Context c) {
                        loc = location;
            mContext = c;
            nEntries = 0;
            entriesUnzipped = 0;
            Log.v(this.toString(), "Exiting decompress constructor.");
        }

        @Override
        protected void onPreExecute() {
            Log.v(this.toString(), "Inside onPreExecute.");
            pd = new ProgressDialog(mContext);
            pd.setTitle("Unzipping folder.");
            pd.setMessage("Unzip in progress.");
            pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            Log.v(this.toString(), "Showing dialog and exiting.");
            pd.show();
        }

               @Override
        protected Boolean doInBackground(Void... params) {
                       //unzip operation goes here.
                       unzipDest = something;  //unzip destination is set here.

                       if(unzip operation is successful) {
                          result = true;
                          index = url pointing to location of unzipped folder.
                       } else {
                         result = false;
                       }
                }

    @Override
        protected void onPostExecute(Boolean result) {
            if(result) {
                if(pd != null) {
                    pd.setTitle("Success");
                    pd.setMessage("folder is now ready for use.");
                    pd.show();
                    pd.dismiss();
                    pd = null;
                    Log.v(this.toString(), "Unzipped.");

                    index = unzipDest + "/someURL";
                    Log.v(this.toString(), "index present in: " + index);
                }
            } else {
                pd = ProgressDialog.show(mContext, "Failure", "Cannot unzip.");
                pd.dismiss();
            }
        }
    }   

我面临的问题:
1.unzipDest和index,和更新的值doInBackground保持为null Unzip及其所有对象.如何确保值保持更新？
2.我知道doInBackground发生在与主UI线程分开的线程中.这是否意味着一旦该线程返回,新线程中更新的任何值都将丢失？

Answer 1

如何确保值保持更新？

它们将被更新,因为它们是成员变量.但是,由于它AsyncTask是异步的,因此在检查时它们可能尚未更新.您可以interface在更新这些值时使用an 来创建回调.这个答案涵盖了如何做到这一点

这是否意味着一旦该线程返回,新线程中更新的任何值都将丢失？

不,他们不应该"迷失".它们可能只是AsyncTask在你检查时没有改变.

由于这不是您的实际代码,我在您尝试访问它们时无法看到,但您可以使用该interface方法或调用需要这些值的函数onPostExecute().您也可以null在尝试访问它们之前进行检查.它取决于您需要的功能和流程,哪种是最佳方式.希望有所帮助.

编辑

在我链接的答案中,您告诉Activity您将在创建单独的内容后使用它interface并implements AsyncResponse在Activity声明中覆盖其方法interface class

public class MainActivity implements AsyncResponse{

然后,在你的Activity静止中,你覆盖你在该类中声明的方法(void processFinish(String output);)

@Override
 void processFinish(String output){  // using same params as onPostExecute()
 //this you will received result fired from async class of onPostExecute(result) method.
   }

然后onPostExecute()在监听器看到它完成的时候调用它是(你的接口类)的delegate.processFinish(result); delegate一个实例AsyncResponse

    public class AasyncTask extends AsyncTask{
public AsyncResponse delegate=null;

   @Override
   protected void onPostExecute(String result) {
      delegate.processFinish(result);
   }

Interface示例取自上面的链接答案,并为了清楚起见进行了调整/评论.所以,如果它对任何人有帮助,请务必提出答案.