如何将值从 Asynctask 返回到活动

Question

如何将值从 Asynctask（不同的类）返回到您调用 Asynctask 的活动，这里我遵循以下链接中给出的说明How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?@HelmiB's

我已经完成了所有操作，并将结果返回给活动的方法 processFinish()，问题是失去了活动控制或焦点，我无法使用 Asynctask 的结果执行进一步的操作，因为我的所有活动的成员都变为空。

如何进行？

protected void onPostExecute(Void result) {
    super.onPostExecute(result);

    if (pDialog != null)
    {
        pDialog.cancel();
    }

    if (StringUtil.hasValue(responseXmlString))
    {
        if (Integer.parseInt(AppUtil.getXpathValue("Result/ErrorNo",AppUtil.buildDocument(responseXmlString))) == 0) 
        {
            asyncResponse.processFinish(responseXmlString);

        }
    }


@Override
public void processFinish(Object output) 
{
    Log.d("Response From Asynchronous task:", (String) output);

    displayView(position,(String) output);
}

private void displayView(int position,String responseXml)
{
    // update the main content by replacing fragments
    boolean isFragment = true;
    Fragment fragment = null;
    /*//For Handling back press 
    if (getIntent().getBooleanExtra("FromPassBook", false) )
    {
        getIntent().putExtra("FromPassBook", false);
        position = 7;
    }
    if (getIntent().getBooleanExtra("toCustomerAcocunts", false) )
    {
        getIntent().putExtra("toCustomerAcocunts", false);
        position = 1;
    }*/

    switch (position)
    {
        case 0:
            fragment = new ChartFragment();
            setTitle(getResources().getString(R.string.wealth));
            break;

        default:
            break;
    }

    if (fragment != null && isFragment)
    {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction ft =fragmentManager.beginTransaction();
        fragmentStack.push(fragment);

        //passing data to fragment
        if (StringUtil.hasValue(responseXml)) 
        {
            Bundle bundle = new Bundle();
            bundle.putString("responseXml", responseXml);
            fragment.setArguments(bundle);
        }

        ft.replace(R.id.frame_container, fragment).commit();

        // update selected item and title, then close the drawer
        listView.setItemChecked(position, true);
        listView.setSelection(position);
        mDrawerLayout.closeDrawer(listView);
    }
    else
    {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }
}
private void callService(int position)
{
    String input = "";
    AsyncCallWS asyncCallWS;
    switch (position)
    {
        case 0:
            input = "<Parm><ProcessID>101</ProcessID><MobileNo>" + mobileNumber + "</MobileNo></Parm>";
            asyncCallWS = new AsyncCallWS(MainActivity.this, input, position,new MainActivity());
            asyncCallWS.execute();
            break;
}

Asynctask class constructor 

`AsyncResponse asyncResponse;

public AsyncCallWS(Context context,String input,int position,AsyncResponse response )
{
    this.context = context;
    this.inputToservice = input;
    this.position = position;
    asyncResponse = response;
}`

Answer 1

嗯，你的问题出在这行代码中：

asyncCallWS = new AsyncCallWS(MainActivity.this, input, position,new MainActivity());

或者，特别是在声明 new MainActivity() 中。您在此处创建MainActivity 类的新实例，然后将其用作回调。显然，它将所有字段都未初始化。使用MainActivity.this 而不是new MainActivity()。请记住，Android 会管理您的所有活动。你永远不想自己创造一个。