Question

我正在开发一个应用程序，我想在splashscreen期间将一些数据存储在sharedPreference中，然后在主活动加载后读取该数据。如果我从MainActivity保存数据，数据将被保存，我可以将其取回。但是，如果我试图在splashscreen中保存数据，我会得到nulpointer的重复。这是一个例外：

java.lang.RuntimeException: An error occured while executing doInBackground()
    at android.os.AsyncTask$3.done(AsyncTask.java:299)
    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
    at java.lang.Thread.run(Thread.java:856)
 Caused by: java.lang.NullPointerException
    at com.example.amandeepsingh.loginregisterandother.SharedPreferncesExecutor.save(SharedPreferncesExecutor.java:22)
    at com.example.amandeepsingh.loginregisterandother.SplashScreenActivityWithAsyncTask$PrefetchData.doInBackground(SplashScreenActivityWithAsyncTask.java:79)
    at com.example.amandeepsingh.loginregisterandother.SplashScreenActivityWithAsyncTask$PrefetchData.doInBackground(SplashScreenActivityWithAsyncTask.java:36)
    at android.os.AsyncTask$2.call(AsyncTask.java:287)

以下是我的示例代码：

SplashScreenActivityWithAsyncTask：

public class SplashScreenActivityWithAsyncTask extends Activity{

    //String now_playing, earned;
    private SharedPreferncesExecutor sharedPreference;
    Activity context;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.splash_screen);

        /**
         * Showing splashscreen while making network calls to download necessary
         * data before launching the app Will use AsyncTask to make http call
         */
        Activity context = this;
        new PrefetchData().execute();

    }

    /**
     * Async Task to make http call
     */
    private class PrefetchData extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // before making http calls
        }

        @Override
        protected Void doInBackground(Void... arg0) {
            sharedPreference = new SharedPreferncesExecutor();
            sharedPreference.save(context,"SchoolData","Updated data from Splash Screen");
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // After completing http call
            // will close this activity and lauch main activity
            Intent i = new Intent(SplashScreenActivityWithAsyncTask.this, MainActivity.class);//Here Main activity is the splash screen.
            //i.putExtra("now_playing", now_playing);
            //i.putExtra("earned", earned);
            startActivity(i);

            // close this activity
            finish();
        }
    }
}

请帮忙。

Answer 1

您的班级成员context为空，因为在onCreate中，声明

Activity context = this;

您隐藏了成员类的可见性，有利于本地成员。为避免歧义，您可以使用NomeOfYourActivity.this（在您的情况下为SplashScreenActivityWithAsyncTask.this），而无需指定任何引用。在您的AsyncTask中更改

sharedPreference.save(context,

到

sharedPreference.save(SplashScreenActivityWithAsyncTask.this,

Answer 2

您在onCreate中声明了一个局部变量，并为其指定了活动的值。不修改成员变量上下文。它保持为空，你得到一个NPE。无需创建任何成员变量。你可以这样做而不是

sharedPreference.save(context,"SchoolData","Updated data from Splash Screen");

使用

sharedPreference.save(SplashScreenActivityWithAsyncTask.this, "SchoolData", 
               "Updated data from Splash screen");

异步任务是SplashScreenActivityWithAsyncTask的非静态内部类，因此它已经有对活动的引用。

在SplashScreen中使用sharedPreference时的NullPointer

2 个答案: