java - Android:SharedPreferences 编辑不起作用

Question

我目前有SharedPreferences设置为如果用户检查 checkBox , SharedPreferences将被编辑为:

public class MainActivity extends Activity {

    public static SharedPreferences prefs;

    public void itemClicked(View v) {
        CheckBox checkBox = (CheckBox)v;
        prefs = this.getSharedPreferences("com.example.app", Context.MODE_PRIVATE);
        if(checkBox.isChecked()) prefs.edit().putBoolean("moveToSettings", false).commit();
        else prefs.edit().putBoolean("moveToSettings", true).commit();
    }    

我希望用户能够编辑这些 SharedPreferences从另一个 Activity ，按按钮 resetapp .为此，这是我在我的 .java 上尝试过的。其他 Activity 的文件:

public class NextActivity extends Activity {

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

        final Button resetapp = (Button)findViewById(R.id.resetapp);

        resetapp.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

                MainActivity.prefs.edit().putBoolean("moveToSettings", true).commit();

            }
        });
    }

然而，当用户按下按钮 resetapp ，应用程序崩溃而不是更改 SharedPreferences .有谁知道为什么会这样？

这是我的 LogCat 的输出:

06-04 10:20:20.455: W/dalvikvm(2808): threadid=1: thread exiting with uncaught exception (group=0x42d5d140)
06-04 10:20:20.545: E/AndroidRuntime(2808): FATAL EXCEPTION: main
06-04 10:20:20.545: E/AndroidRuntime(2808): Process: com.example.MyFirstApp, PID: 2808
06-04 10:20:20.545: E/AndroidRuntime(2808): java.lang.NullPointerException
06-04 10:20:20.545: E/AndroidRuntime(2808):     at com.example.MyFirstApp.NextActivity$1.onClick(NextActivity.java:32)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.view.View.performClick(View.java:4438)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.view.View$PerformClick.run(View.java:18422)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.os.Handler.handleCallback(Handler.java:733)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.os.Handler.dispatchMessage(Handler.java:95)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.os.Looper.loop(Looper.java:136)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at java.lang.reflect.Method.invokeNative(Native Method)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at java.lang.reflect.Method.invoke(Method.java:515)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-04 10:20:20.545: E/AndroidRuntime(2808):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

您可以为您的应用程序编写一个 SharedPrefance 类，并在其中编写一些 setter 和 getter 方法并使用它们。它;管理代码很容易，你永远不会对你的应用程序偏好感到困惑。

    public class Pref {
    private static final String USER_ID = "userID";
    private static final String PREF_NAME = "Tim";

    private static Pref instance;
    private SharedPreferences preferences;
    private Editor editor;

    private Pref(Context context) {
        preferences = context.getSharedPreferences(PREF_NAME, 0);
        editor = preferences.edit();
    }

    public static Pref getInstance(Context context) {
        return instance == null ? new Pref(context) : instance;
    }

    public void setUserID(String userID) {
        editor.putString(USER_ID, userID).commit();
    }

    public String getUserID() {
        return preferences.getString(USER_ID, "");
    }
}

从应用程序中，您只需调用即可访问它

Pref.getInstance(this).setUserID("whatever");
Pref.getInstance(this).getUserID();