Question

I’m attempting to save my array of players into a JSONArray, convert it to a string, place it into SharedPreferences then convert it back. The JSONArray I’m getting back when reloading my app with my current attempt is throwing runtime exceptions/ClassCast Exceptions if I attempt to access any of the Player instances within the array.

Where am I going wrong?

JSONArray savedPlayers;
SharedPreferences prefs;
@Override
public void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.indie);

    savedPlayers = new JSONArray();

    prefs = getSharedPreferences("appData", 0);
    String jsonString = prefs.getString("playerString", null);

    //Restores playerArray if any players have been saved in the past
    if(jsonString != null)
    {
        try 
        {

            savedPlayers = new JSONArray(JSONString);
            MyListView.players.clear();
            MyListView.ids.clear();
            for(int i = 0; i < savedPlayers.length(); i++)
            {
                MyListView.players.add(((Player) savedPlayers.get(i)).getName()); //Error
                MyListView.ids.add(((Player) savedPlayers.get(i)).getSaveId());
            }
        } 
        catch (JSONException e) 
        {
            e.printStackTrace();
        }
    }
}

//If there are savedPlayers converts the JSONArray to a string and saved it within SharedPreferences
@Override
protected void onPause() 
{
    if(savedPlayers != null)
    {
        SharedPreferences.Editor editor = getSharedPreferences("appData", 0).edit();
        String jsonString = savedPlayers.toString();
        editor.putString("playerString", jsonString).commit();
    }
    super.onPause();
}

JSONString:
["en.deco.android.livehud.Player@44eba878","en.deco.android.livehud.Player@44ebec68"]

Logcat:

04-16 22:31:13.765: ERROR/AndroidRuntime(7496): Uncaught handler: thread main exiting due to uncaught exception
04-16 22:31:13.785: ERROR/AndroidRuntime(7496): java.lang.RuntimeException: Unable to start activity ComponentInfo{en.deco.android.livehud/en.deco.android.livehud.GUI}: java.lang.ClassCastException: java.lang.String
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.os.Looper.loop(Looper.java:123)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread.main(ActivityThread.java:4363)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at java.lang.reflect.Method.invokeNative(Native Method)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at java.lang.reflect.Method.invoke(Method.java:521)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at dalvik.system.NativeStart.main(Native Method)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496): Caused by: java.lang.ClassCastException: java.lang.String
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at en.deco.android.livehud.GUI.onCreate(GUI.java:102)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
04-16 22:31:13.785: ERROR/AndroidRuntime(7496):     ... 11 more
04-16 22:32:57.775: ERROR/AndroidRuntime(7537): Uncaught handler: thread main exiting due to uncaught exception
04-16 22:32:57.795: ERROR/AndroidRuntime(7537): java.lang.RuntimeException: Unable to start activity ComponentInfo{en.deco.android.livehud/en.deco.android.livehud.GUI}: java.lang.ClassCastException: java.lang.String
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.os.Looper.loop(Looper.java:123)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread.main(ActivityThread.java:4363)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at java.lang.reflect.Method.invokeNative(Native Method)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at java.lang.reflect.Method.invoke(Method.java:521)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at dalvik.system.NativeStart.main(Native Method)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537): Caused by: java.lang.ClassCastException: java.lang.String
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at en.deco.android.livehud.GUI.onCreate(GUI.java:102)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
04-16 22:32:57.795: ERROR/AndroidRuntime(7537):     ... 11 more

Answer 1

You are currently creating a JSONArray using the toString representation of each Player object, which results in an array of strings which don’t contain any information from the fields of the Player itself. If you are going to use the JSONArray/JSONObject classes, then you need to instead create a JSONObject object for each of your players, and add those to the JSONArray. For example, the following code would create a JSONObject, add the name of your player to the object, and then add it to the JSONArray:

JSONObject playerJsonObject = new JSONObject();
playerJsonObject.put("name", player.getName());
jsonArray.put(playerJsonObject);

However, a much simpler way of doing JSON serialization is to use GSON:
http://code.google.com/p/google-gson/