问题描述

总的来说，我是 Android 开发和 Java 的新手.这是基本设置:我有一个带有 AsyncTask 的启动画面，用于检查服务器可用性.在 this 线程之后，我在我的活动中进行了回调.这比在 OnPostExecute() 中做工作更有意义，因为我想在不同的活动中重用这个任务.

I'm super new to Android development and Java in general. Here's the basic setup: I have a splash screen with an AsyncTask to check server availability. Following this thread I made a callback in my activity. This makes more sense than doing the work in OnPostExecute() as I want to reuse this task in different activities.

但是，在我的回调中，我会检查状态是否正常.如果是，它应该启动下一个活动.但是从我的回调上下文来看，我不知道如何获取我的 Activity 引用，我需要将其作为 Intent 的参数.

However, in my callback I do a check if the status is okay. If it is, it should launch the next activity. But from the context of my callback, I don't get how I can get my Activity reference, which I need as a parameter for the Intent.

这是我在 OnCreate 下的 Activity 中的代码:

This is the code in my Activity under OnCreate:

    //Check server status
    CheckServiceTask t = new CheckServiceTask(new OnTaskCompleted<ShaggyServiceStatus>() {
        @Override
        public void onTaskCompleted(ShaggyServiceStatus result) {
            Log.i(TAG, "Callback. Result: " + result.getStatus());
            ProgressBar pb = (ProgressBar) findViewById(R.id.splash_progress);
            pb.setVisibility(View.INVISIBLE);

            if (result.getStatusCode() == 999){
                TextView t = (TextView) findViewById(R.id.splash_status_text);
                t.setText(result.getStatus());
                return;
            }

            Intent i = new Intent(getActivity(), LoginActivity.class);
            startActivity(i);
            finish();

        }
    });

    t.execute();

失败的部分是 getActivity().该呼叫不可用.使用 this 会引发错误(我理解，因为我在 OnTaskCompleted 的上下文中).

The part where this fails is at getActivity(). That call is not available. Using this throws an error (which I understand, as I'm in the context of OnTaskCompleted).

为了完整起见，这是 OnTaskCompleted 的接口:

For completeness, this is the interface for OnTaskCompleted:

public interface OnTaskCompleted<T> {
    public void onTaskCompleted(T result);
}

这是 CheckServiceTask 类:

And this is the CheckServiceTask class:

public class CheckServiceTask extends AsyncTask<Void, Void, ShaggyServiceStatus>{
    private static final String TAG = "coo";

    public OnTaskCompleted<ShaggyServiceStatus> listener;

    public CheckServiceTask (OnTaskCompleted<ShaggyServiceStatus> l){
        this.listener = l;
    }

    @Override
    protected ShaggyServiceStatus doInBackground(Void... params) {
        try {
            Log.i(TAG, "Connecting to server...");
            //TODO: Make this a setting
            final String url = "https://someplace.com/status";
            RestTemplate restTemplate = new RestTemplate();
            restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            //restTemplate.postForObject("url", bodyObject, ShaggySer.class);
            ShaggyServiceStatus sss = restTemplate.getForObject(url, ShaggyServiceStatus.class);
            Log.d(TAG, "Got the status.");
            return sss;
        } catch (Exception e) {
            //TODO: Exception handling
            Log.e(TAG, e.getMessage(), e);
        }

        //If we're here, it's not okay.
        ShaggyServiceStatus r = new ShaggyServiceStatus("Cannot connect to server", 999, "none");

        return r;
    }

    @Override
    protected void onPostExecute(ShaggyServiceStatus result) {
        super.onPostExecute(result);
        listener.onTaskCompleted(result);
    }
}

推荐答案

Use CurrentClassName.this

Intent i = new Intent(CurrentClassName.this, LoginActivity.class);

getActivity():与 Fragments 一起使用

getActivity(): used with Fragments

返回当前与此片段关联的 Activity.

Return the Activity this fragment is currently associated with.

class.this 与嵌套类时的 this 不同.

class.this isn't the same as this when you have nested class.

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