当我把它放在一个单独的 java 文件中时，我的 Asyntask 不工作

Question

我将所有异步任务放在一个文件中，但它变得有点混乱，所以我决定将它们放在单独的文件/类中。我不断收到一些错误。我做错了什么，谢谢

在我的 mainActivity.and 错误中：

//Handler for the PIN. Leads to the Internet Intent
public void log_in(View v) {



    new TwitterLogin(null, null, null).execute();

    }

 Description    
    The constructor TwitterLogin() is undefined MainActivity.java

TwitterLogin.java

//Starts an intent that loads up a web browser and asks the user to log in to twitter
// and get a pin#
public class TwitterLogin extends AsyncTask<URL, Integer, RequestToken> {

    private Context context;
    private Activity Activity;
    public Twitter twitter = TwitterFactory.getSingleton();
    public RequestToken requestToken = null;

    public TwitterLogin(Context context, Twitter twitter,
            RequestToken requestToken) {
        this.context = context;
        this.twitter = twitter;
        this.requestToken = requestToken;


    }

    @Override
    protected RequestToken doInBackground(URL... arg0) {

        try {
            requestToken = twitter.getOAuthRequestToken();
            Log.i("Got Request Token", "food4thought");
        } catch (TwitterException e) {
            Log.i("Failed to get Request Token", "food4thought");
        }

        // Log.i(requestToken.getAuthorizationURL(), "food4thought");
        // requestToken.getAuthorizationURL();
        // log_in.setText();

        try {
            Intent browserIntent = new Intent(Intent.ACTION_VIEW,
                    Uri.parse(requestToken.getAuthorizationURL()));
            context.startActivity(browserIntent);
        }

        catch (NullPointerException e) {
            ((Activity) context).runOnUiThread(new Runnable() {
                public void run() {
                    Toast.makeText(context.getApplicationContext(),
                            "Unable to log in, No access to the Internet.",
                            Toast.LENGTH_LONG).show();

                }
            });

        }

        return null;
    }

}

这里是日志

04-24 21:27:23.635: E/AndroidRuntime(19644): Process: com.example.food4thought, PID: 19644
04-24 21:27:23.635: E/AndroidRuntime(19644): java.lang.RuntimeException: An error occured while executing doInBackground()
04-24 21:27:23.635: E/AndroidRuntime(19644):    at android.os.AsyncTask$3.done(AsyncTask.java:300)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.lang.Thread.run(Thread.java:841)
04-24 21:27:23.635: E/AndroidRuntime(19644): Caused by: java.lang.NullPointerException
04-24 21:27:23.635: E/AndroidRuntime(19644):    at com.example.food4thought.TwitterLogin.doInBackground(TwitterLogin.java:39)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at com.example.food4thought.TwitterLogin.doInBackground(TwitterLogin.java:1)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at android.os.AsyncTask$2.call(AsyncTask.java:288)
04-24 21:27:23.635: E/AndroidRuntime(19644):    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
04-24 21:27:23.635: E/AndroidRuntime(19644):    ... 4 more

Answer 1

您的constructor 需要3 个params...第一个是Context。您已将null 传递给所有这些，这意味着您在此处获得NPE

context.startActivity(browserIntent);

这里

requestToken = twitter.getOAuthRequestToken();

这里

 Uri.parse(requestToken.getAuthorizationURL()));

因为context 是null。

你想把它改成

// assuming MainActivity is the name of your Activity
new TwitterLogin(MainActivity.this, null, null).execute(); 

twitter 和 requestToken 也是 null 看起来你首先引用 twitter 这可能会给你的例外。您正在为这些变量传递null，然后尝试使用发送的null 参数初始化它们。

编辑

这也是一团糟，因为您不应该尝试更新 doInBackground() 中的 UI

catch (NullPointerException e) {
        ((Activity) context).runOnUiThread(new Runnable() {
            public void run() {
                Toast.makeText(context.getApplicationContext(),
                        "Unable to log in, No access to the Internet.",
                        Toast.LENGTH_LONG).show();

使用AsyncTask为您提供的方法。

AsyncTask

Please also see this answer