我如何从异步任务中返回结果[重复]

Question

我一直在使用异步任务来访问 Web 服务器并使用结果更新控件。这有缺点，即它使异步方法特定于控件并阻止我再次使用返回的字符串。

如何从异步调用 onPostExecute 返回结果字符串？我怎么称呼它？我似乎无法让我的代码做到这一点。线程应该没有问题，因为我有一个对话框会冻结 UI，直到工作完成。

我典型的 asyncTask 代码如下

class GetDataFromServer extends AsyncTask<String, String, String>
{
     * */
    // Progress Dialog
    private ProgressDialog qDialog;
    private Context context;
    private String dialogString;
    private ArrayList<String[]> newLoginResult;

    // JSON parser class
    String url_newGame ="http://xxxxxx.php";

    public myAsyncMethos(String dialogMessage, Context con)
    {
        this.qDialog =  new ProgressDialog(con);
        this.dialogString = dialogMessage;
        this.context = con;
    }

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute()
    {
        super.onPreExecute();
        qDialog = new ProgressDialog(this.context);
        qDialog.setMessage(this.dialogString);
        qDialog.setIndeterminate(false);
        qDialog.setCancelable(false);
        qDialog.show();
    }

    @Override
    protected JSONObject doInBackground(String... args)
    {
        //MAKE SERVER CALL and cast to JSONOBject

        return jsonNewUser;
    }

    public void onPostExecute(JSONObject jsonString)
    {

         // dismiss the dialog after getting response
        qDialog.dismiss();
//I WANT TO RETURN A STRING HERE BUT KEEP GETTING SYNTAX ERRORS BEFORE RUNTIME


    }
}

Answer 1

我会亲自为您的类添加一个回调，然后在运行 onPostExecute 后，将您的回调触发到主类上的侦听器。

class GetDataFromServer extends AsyncTask<String, String,JSONObject>
{
    // Progress Dialog
    private ProgressDialog qDialog;
    private Context context;
    private String dialogString;
    private ArrayList<String[]> newLoginResult;
    private InformComplete myCallback;

    public GetDataFromServer(String dialogMessage, Context con,InformComplete callback)
    {
        this.qDialog =  new ProgressDialog(con);
        this.dialogString = dialogMessage;
        this.context = con;
        this.myCallback=callback;
    }

    @Override
    protected void onPreExecute()
    {
        // set up your dialog
    }

    @Override
    protected JSONObject doInBackground(String... args)
    {
        JSONObject jsonNewUser=new JSONObject();
        return jsonNewUser;
    }

    public void onPostExecute(JSONObject jsonString)
    {
        qDialog.dismiss();
        myCallback.PostData(jsonString);
    }
    public interface InformComplete
    {
        public void PostData(JSONObject result);
    }
}

然后从你的调用类中，你会有这样的东西......

    private void callTheAsyncThing
    {
        GetDataFromServer gds=new GetDataFromServer("please wait", this, letMeKnow);
        gds.execute(params);
    }

    private InformComplete letMeKnow=new InformComplete()
    {
        public void PostData(JSONObject result)
        {
            // we now have the data in the calling class
        }
    };

Answer 2

您不能在 AsynTask 的方法中返回值，因为它曾经返回 void 元素。因此，您可以实例化 global var foe example，并将值设置为它。喜欢... `

class GetDataFromServer extends AsyncTask<String, String, String>
{
     * */
    // Progress Dialog
    private ProgressDialog qDialog;
    private Context context;
    private String dialogString;
    private ArrayList<String[]> newLoginResult;
    private String value;

    // JSON parser class
    String url_newGame ="http://xxxxxx.php";

    public myAsyncMethos(String dialogMessage, Context con)
    {
        this.qDialog =  new ProgressDialog(con);
        this.dialogString = dialogMessage;
        this.context = con;
    }

    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute()
    {
        super.onPreExecute();
        qDialog = new ProgressDialog(this.context);
        qDialog.setMessage(this.dialogString);
        qDialog.setIndeterminate(false);
        qDialog.setCancelable(false);
        qDialog.show();
    }

    @Override
    protected JSONObject doInBackground(String... args)
    {
        //MAKE SERVER CALL and cast to JSONOBject

        return jsonNewUser;
    }

    public void onPostExecute(JSONObject jsonString)
    {

         // dismiss the dialog after getting response
        qDialog.dismiss();
        value = "Whatever you want";
    }
    public void setValue(String value){
         this.value=value;
    }
    public String getValue(){
         return this.value;
    }
}`

然后使用它。有一种方法可以退货。顺便说一句，你不能改变回报。

Answer 3

onPostExecute 的方法不是程序员调用，它是由 AsyncTask 实例调用的。如果你想从一个异步任务返回一个结果，你可以发送一个参数到 GetDataFromServer ，在 onPostExecute 的方法中，你给他新的值，然后就可以使用Handler来发送消息了。

Answer 4

当您尝试在 onPostExecute 方法中获取字符串时，您在 doInBackground 方法中返回 JSONObject。

public void onPostExecute(JsonObject jsonString)
{
     // dismiss the dialog after getting response
     qDialog.dismiss();
     //I WANT TO RETURN A STRING HERE BUT KEEP GETTING SYNTAX ERRORS BEFORE RUNTIME
}