español - java.lang.NullPointerException: intento de invocar un método virtual en una referencia de objeto nulo

javac error cannot find symbol

Question

Esta pregunta ya tiene respuestas aquí :

Cerrado hace 4 años .

¿Qué es una excepción NullPointerException y cómo la soluciono? (12 respuestas)

Estoy tratando de guardar el nombre del jugador en preferencia compartida y hacer que se muestre en otra actividad al recuperarlo en preferencia compartida pero mi aplicación falla.

EXCEPCIÓN FATAL: principal

 Process: plp.cs4b.thesis.drawitapp, PID: 1970
java.lang.RuntimeException: Unable to start activity ComponentInfo{plp.cs4b.thesis.drawitapp/plp.cs4b.thesis.drawitapp.PlayGame}: java.lang.NullPointerException: Attempt to invoke virtual method ''java.lang.String plp.cs4b.thesis.drawitapp.Player.getName()'' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method ''java.lang.String plp.cs4b.thesis.drawitapp.Player.getName()'' on a null object reference
at plp.cs4b.thesis.drawitapp.PlayGame.onCreate(PlayGame.java:20)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
... 10 more

Códigos

Player.java

public class Player {
private Context context;
private SharedPreferences prefSettingsU;
private SharedPreferences.Editor prefEditorU;
private static final int PREFERENCE_MODE_PRIVATE = 0;
private static final String MY_UNIQUE_PREF_FILE = "DrawItApp";
public Player(Context context, String name) {
this.context = context;
saveName(name);
}
public void saveName(String n) {
prefSettingsU = context.getSharedPreferences(MY_UNIQUE_PREF_FILE, PREFERENCE_MODE_PRIVATE);
prefEditorU = prefSettingsU.edit();
prefEditorU.putString("keyName", n);
prefEditorU.commit();
}
public String getName(Context ctx) {
prefSettingsU = ctx.getSharedPreferences(MY_UNIQUE_PREF_FILE, PREFERENCE_MODE_PRIVATE);
String name = prefSettingsU.getString("keyName", "ANONYMOUS");
return name;
}

PlayGame.java

public class PlayGame extends Activity {
private TextView welcomePlayer;
private ListView createdGames;
private Player mPlayer;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.play_game);
welcomePlayer = (TextView) findViewById (R.id.tvPlayerName);
welcomePlayer.setText("Welcome Back, " + String.valueOf(mPlayer.getName(this)) + " !");
createdGames = (ListView) findViewById (R.id.listCreatedGames);
// adapter etc
createdGames.setEmptyView(findViewById (R.id.tvNoGames));
}

PlayerName.java

public class PlayerName extends Activity {
private EditText playerName;
private Player mPlayer;
public static Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.player_name);
context = this;
playerName = (EditText) findViewById (R.id.etName);
}
public void onC_Confirm(View btnclick) {
mPlayer = new Player(context, String.valueOf(playerName.getText()));
//mPlayer.saveName();
Intent intent = new Intent(PlayerName.this, PlayGame.class);
startActivity(intent);
}
public void onC_testShPref(View btnclick) {
Intent intent = new Intent(PlayerName.this, PlayGame.class);
startActivity(intent);
}

Answer 1

Su bloqueo de la aplicación está en:

welcomePlayer.setText("Welcome Back, " + String.valueOf(mPlayer.getName(this)) + " !");

porque mPlayer=null .

Olvidó inicializar Player mPlayer en su actividad PlayGame.

mPlayer = new Player(context,"");