AsyncTask类的正确方式如何等待另一个AsyncTask类完成其过程

Question

我正在做一个访问Web服务的应用程序，并使用从中获取的JSON创建一个对象并将其用于代码中。 即使我的应用程序正常运行，我也不知道它编写得很好且完美无缺。

我将解释一下，然后放入一些示例代码进行演示...首先，我创建了一个带有EditText和Button的Activity，用户将在其中键入代码并单击该按钮以访问我的数据库并检查是否它存在。 主要是在这里：在我的button.OnClickListener中，我检查EditText上是否有东西，以及是否有Internet连接<-（我从没遇到任何问题），然后我调用了从AsyncTask，它在后台访问WebService并从中获取一个对象。 而且只有在此之后，我才能从此RestClient获得结果。 我的解决方案是启动一个新的AsyncTask，等待我的RestClient，然后启动获取对象的过程。

这是我的restClient的代码示例，该代码从Web服务返回通用对象：

public class RestClient<t>  extends AsyncTask<String, String, String> {

private Class<t> tClass;
private t ObjReturn;

public RestClient(Class<t> tClass)
{
    this.tClass = tClass; 
}

public Object getObjectResponse(){
    return ObjetoDeRetorno;
}

@Override
protected void onPreExecute() {
    super.onPreExecute();
}

@Override
protected String doInBackground(String... OnlyTheURL) {
    String urlString = OnlyTheURL[0];
    String error = null;
    WebApiDeRetorno = new WebApiRetorno();
    try {
        Log.i("RestClient","Starting connection");

        URL url = new URL(urlString);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");

        connection.connect();

        String result = convertStreamToString(connection.getInputStream());

        connection.disconnect();

        JSONObject jsonObject = new JSONObject(result);

        String obj = jsonObject.get("returnObject").toString();

        Gson gson = new Gson();
        ObjReturn = gson.fromJson(obj, tClass);


    } catch (IOException | JSONException e) {
        e.printStackTrace();
        return error;
    }
    return null;
}

@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    }
}

我的臀部功能：

buttonConfirmar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {


            restClient = new RestClient<>(MyObject.class);

            restClient.execute(getString(R.string.WebServiceURL));
            new WhenWebServiceConnectionFinished().execute();

        }
    });

在RestClient之后执行并需要等待其完成的另一个AsyncTask类：

private class WhenWebServiceConnectionFinished extends AsyncTask<String, Void, Boolean> {
    @Override
    protected void onPreExecute() {
        progressDialog.show();
        super.onPreExecute();
    }

    @Override
    protected Boolean doInBackground(String... params) {

        //THIS IS WHAT I DON'T KNOW IF IT'S OK TO DO:
        do {
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        } while (restClient.getStatus() != AsyncTask.Status.FINISHED);
        //WAITING THE restClient.getStatus CHANGE TO FINISHED WITH Thread.sleepS.

        if (checkWebApiRetorno()) {
            objectReturnFromWebApi = (MyObject) restClient.getObjectResponse();

            Intent intent = new Intent(thisActivity, NewActivity.class);
            startActivity(intent);
            finish();
            return true;
        }
        return false;
    }

    @Override
    protected void onPostExecute(Boolean success) {
        if (progressDialog.isShowing())
            progressDialog.dismiss();

        if (!success)
            dialogBuilder.create().show();

        super.onPostExecute(success);
    }
}

Answer 1

将回调添加到第一个AsyncTask并仅在第一个AsyncTask触发onPostExecute之后运行第二个回调

就像是

public interface AsyncFinishedCallback{
    public void onAsyncFinished();
}

并在第一个AsyncTask做这样的构造函数

public RestClient(Class<t> tClass, AsyncFinishedCallback callback)
{
    this.tClass = tClass; 
    this.callback = callback; //declare it somewhere as a field
}

然后

@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    if(callback!=null)
        callback.onAsyncFinished();
    }
}

比按钮功能

buttonConfirmar.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {


        restClient = new RestClient<>(MyObject.class, new AsyncFinishedCallback(){
    @Override
    public void onAsyncFinished(){
            new WhenWebServiceConnectionFinished().execute();
    }
});

        restClient.execute(getString(R.string.WebServiceURL));

Answer 2

尝试以下操作：当您从第一个Async task获取结果时启动另一个任务，请使用AsyncTask<String, String, Boolean>

    public class RestClient<t>  extends AsyncTask<String, String, Boolean> {

private Class<t> tClass;
private t ObjReturn;

public RestClient(Class<t> tClass)
{
    this.tClass = tClass; 
}

public Object getObjectResponse(){
    return ObjetoDeRetorno;
}

@Override
protected void onPreExecute() {
    super.onPreExecute();
}

@Override
protected Boolean doInBackground(String... OnlyTheURL) {
    String urlString = OnlyTheURL[0];
    String error = null;
    WebApiDeRetorno = new WebApiRetorno();
    try {
        Log.i("RestClient","Starting connection");

        URL url = new URL(urlString);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");

        connection.connect();

        String result = convertStreamToString(connection.getInputStream());

        connection.disconnect();

        JSONObject jsonObject = new JSONObject(result);

        String obj = jsonObject.get("returnObject").toString();

        Gson gson = new Gson();
        ObjReturn = gson.fromJson(obj, tClass);
        return true;

    } catch (IOException | JSONException e) {
        e.printStackTrace();
        return  false;;
    }
  return true;
}

@Override
protected void onPostExecute(Boolean result) {
    if (result) {
            //success occurs task finish
             new WhenWebServiceConnectionFinished().execute();
         } else {
                //error occurs 
            }
        }
    }
}