将列表保存到sharedPref。 使用GSON Nullpointer错误

Question

I have the following code:

public class CustomGesture extends Activity {

private static Spinner spinner1, spinner2;
private static Button btn;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.custom_gesture);
    spinner1 = (Spinner) findViewById(R.id.spinner1);
    spinner2 = (Spinner) findViewById(R.id.spinner2);
    // list.add("peepu");
    // list.add("Cheecki");
    List<String> list = new ArrayList<String>();
    list.add("cheeku");
    list.add("matthu");
    SharedPreferences appSharedPrefs = PreferenceManager
            .getDefaultSharedPreferences(this.getApplicationContext());
    Editor prefsEditor = appSharedPrefs.edit();
    Gson gson = new Gson();
    String json = gson.toJson(list);
    prefsEditor.putString("MyObject", json);
    prefsEditor.commit();
    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_spinner_item, list);
    dataAdapter
            .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner1.setAdapter(dataAdapter);
    btn = (Button) findViewById(R.id.btnSubmit);
    btn.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                     SharedPreferences appSharedPrefs = PreferenceManager
                              .getDefaultSharedPreferences(getApplicationContext());
                              Gson gson = new Gson();
                              String json = appSharedPrefs.getString("MyObject", "");
                              List<String> list = gson.fromJson(json, null);
                    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(getApplicationContext(), android.R.layout.simple_spinner_item, list);
                    dataAdapter
                            .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                    spinner2.setAdapter(dataAdapter);
                }
            }).start();
        }
    });
}

}

the error I'm getting is the following :

04-13 13:50:20.066: E/AndroidRuntime(2358): FATAL EXCEPTION: Thread-5592
04-13 13:50:20.066: E/AndroidRuntime(2358): java.lang.NullPointerException
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.internal.$Gson$Preconditions.checkNotNull($Gson$Preconditions.java:35)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.reflect.TypeToken.<init>(TypeToken.java:72)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.reflect.TypeToken.get(TypeToken.java:296)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.Gson.fromJson(Gson.java:801)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.Gson.fromJson(Gson.java:768)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.Gson.fromJson(Gson.java:717)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.google.gson.Gson.fromJson(Gson.java:689)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at com.winacro.Bsquares.CustomGesture$1$1.run(CustomGesture.java:60)
04-13 13:50:20.066: E/AndroidRuntime(2358):     at java.lang.Thread.run(Thread.java:841)

I think this error is because Im using null as a parameter in the fromJSON ,but what to use instead of the null parameter I think I cannot use a list there?

Answer 1

SharedPrefrences用于存储少量数据，例如标志和静态字符串，您寻求一种解决方法来存储json格式的字符串，该字符串适用于非常小的json对象，否则您需要使用sqlite， 这是一个指南