嘗試檢索Sharedpreferences會使應用程序崩潰

Question

我剛接觸Android，后來習慣了iOS。 共享首選項有點困難。 我基本上是第一次在我的設置視圖中初始化，最高得分為0。

現在在另一個游戲視圖中，當我嘗試檢索此分數並將其與當前分數進行比較以更新它時，它崩潰了。 嘗試讀取它后，應用程序崩潰。

這是在設置頁面中初始化的：

public void onWindowFocusChanged(boolean hasFocus) {
    // TODO Auto-generated method stub

    // similar to view did appear
    System.out.println("Settings viewdidappear");
    super.onWindowFocusChanged(hasFocus);

    int firstTime = 10;
    SharedPreferences preferences = this.getSharedPreferences("Settings", Context.MODE_PRIVATE);

    int getVar = preferences.getInt("CheckVar", 0);

    // set the value first time if not existing already
    if (getVar != 10) {

        System.out.println("Settings not existant: " + getVar);
        SharedPreferences.Editor editor = preferences.edit();
        getVar = 10;
        editor.putInt("CheckVar", getVar);
        editor.putInt("HighScore", 0);
        editor.commit();

        // add loading for save score


    } else {
        System.out.println("Settings Already Exists: " + getVar);
    }

}

這是在游戲頁面中：

public class GameLogic extends View {

    SharedPreferences settings;

    public void save(Context context) {
        System.out.println("Running save");

        settings = context.getSharedPreferences("Settings", Context.MODE_PRIVATE);
        int getVar = settings.getInt("HighScore", 0);
        if (getVar > total_score) {
            System.out.println("Putting new value " + total_score);
            SharedPreferences.Editor editor = settings.edit();
            getVar = total_score;
            editor.putInt("HighScore", getVar);
            editor.commit();
        } else {
            System.out.println("Previous score is higher " + getVar);
        }

    }


    public void DidILose() {
        score();

        if (TappedMine == 2) {

            save(null);

            flag_for_loss = 1;
            AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
                    getContext());
            alertDialogBuilder.setTitle("Game Over");
            alertDialogBuilder
                    .setMessage("Play again!  \nScore: " + total_score + "\nTime: " + 
                            time_done + " seconds" + "\n Unflagged Mines:" + unflagged_mines)
                    .setCancelable(false)
                    .setPositiveButton("Yes",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog,
                                                    int id) {
                                    ResetTheGame();
                                }
                            }
                    );
            AlertDialog alertDialog = alertDialogBuilder.create();
            alertDialog.show();
        }
    }

}

Answer 1

您調用save(null);

並嘗試使用該參數訪問該對象，該參數為null ，從而導致NullPointerException ，使您的應用程序崩潰

 public  void save(Context context) {
        System.out.println("Running save");
        settings = context.getSharedPreferences("Settings", Context.MODE_PRIVATE);