java - 从其他 Activity 中的 AsyncTask 返回值

Question

这是代码，抱歉我的英语。

错误是:NullPointerException。 1个Activity类“menu_fei”，1个Cliente类，1个返回值接口(interface)。

public interface AsyncResponse {
    void processFinish(String output);
}

public class Cliente extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null; // 

    public Cliente(AsyncResponse delegate) {
        this.delegate = delegate;
    }

    public Cliente(String type) {
        this.excute();
    }

    // in method doInBackground return correctly string

    protected void onPostExecute(String result) {
        // Log.d("OutPut",result); // it's ok String!
        if (result == null)
            Log.d("OUTPUT", "NULL"); // for example
        else
            delegate.processFinish(result); // --- ERROR !! --- but result not NUll
    }
}

<小时/>

public class Menu_fei extends Activity implements AsyncResponse {

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        Cliente asyncTask =new Cliente(this);
        asyncTask.delegate = this;  
        new Cliente("menu_fei");    
    }
}

Answer 1

Cliente asyncTask =new Cliente(this);
asyncTask.delegate = this;  
new Cliente("menu_fei");  

您的代码的问题在于，在第三行中，您正在创建 Cliente 的新实例，而没有设置委托(delegate)。要修复您只需运行

Cliente asyncTask =new Cliente(this);
asyncTask.execute();