java - 如何处理来自 AsyncTask 的返回值

Question

我正在使用具有以下签名的 AsyncTask 类:

public class ApiAccess extends AsyncTask<List<NameValuePair>, Integer, String> {
    ...
private String POST(List<NameValuePair>[] nameValuePairs){
    ...
    return response;
}
}

protected String doInBackground(List<NameValuePair>... nameValuePairs) {
    return POST(params);
}

我正在尝试通过以下方式从其他类调用它:

ApiAccess apiObj = new ApiAccess (0, "/User");
// String signupResponse = apiObj.execute(nameValuePairs);
String serverResponse = apiObj.execute(nameValuePairs); //ERROR

但在这里我得到了这个错误:

Type mismatch: cannot convert from AsyncTask<List<NameValuePair>,Integer,String> to String

为什么当我在类扩展行中指定 String 作为第三个参数时？

Answer 1

你可以通过在返回的AsyncTask上调用AsyhncTask的get()方法来获取结果，但是它会在等待获取结果时将它从一个异步任务变成一个同步任务。

String serverResponse = apiObj.execute(nameValuePairs).get();

由于您将 AsyncTask 放在一个单独的类中，因此您可以创建一个接口(interface)类并在 AsyncTask 中声明它，并将您的新接口(interface)类实现为您希望从中访问结果的类中的委托(delegate)。一个很好的指南在这里:How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class? .

我将尝试将上述链接应用到您的上下文中。

(IApiAccessResponse)

public interface IApiAccessResponse {
    void postResult(String asyncresult);
}

(ApiAccess)

public class ApiAccess extends AsyncTask<List<NameValuePair>, Integer, String> {
...
    public IApiAccessResponse delegate=null;
    protected String doInBackground(List<NameValuePair>... nameValuePairs) {
        //do all your background manipulation and return a String response
        return response
    }

    @Override
    protected void onPostExecute(String result) {
        if(delegate!=null)
        {
            delegate.postResult(result);
        }
        else
        {
            Log.e("ApiAccess", "You have not assigned IApiAccessResponse delegate");
        }
    } 
}

(你的主类，它实现了 IApiAccessResponse)

ApiAccess apiObj = new ApiAccess (0, "/User");
//Assign the AsyncTask's delegate to your class's context (this links your asynctask and this class together)
apiObj.delegate = this;
apiObj.execute(nameValuePairs); //ERROR

//this method has to be implement so that the results can be called to this class
void postResult(String asyncresult){
     //This method will get call as soon as your AsyncTask is complete. asyncresult will be your result.
}