如何处理来自AsyncTask的返回值

问题描述

我使用的AsyncTask 类具有以下签名：

I am using AsyncTask class with the following signature:

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);
}

我试图通过从其他类调用它：

I am trying to call it from other class through:

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

但在这里我得到这个错误：

But here I get this error:

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

这是为什么我指定当字符串在类延长线的第三个参数？

Why is that when i have specified String as the third parameter in Class extension line?

推荐答案

您可以通过在返回的AsyncTask的呼叫AsyhncTask的get（）方法得到的结果，但它会把它从异步任务进入一个同步的任务，因为等待得到的结果。

You can get the result by calling AsyhncTask's get() method on the returned AsyncTask, but it will turn it from an asynchronous task into a synchronous task as it waits to get the result.

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

既然你有你的AsyncTask在一个单独的类，你可以创建一个接口类，并在AsyncTask的声明，并实现新的接口类的代表在您希望从访问结果的类。一个很好的指南是在这里：How得到OnPostExecute（）为主要活动的结果，因为AsyncTask的是一个单独的类？。

我会尝试应用上面的链接到你的环境。

I will attempt to apply the above link to your context.

（IApiAccessResponse）

(IApiAccessResponse)

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

（ApiAccess）

(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");
        }
    }
}

（主类，它实现IApiAccessResponse）

(Your main class, which implements 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.
}

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