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java.lang.NullPointerException：nullオブジェクト参照で仮想メソッドを呼び出そうとしました

共有設定でプレイヤーの名前を保存し、共有設定で再度取得することで別のアクティビティで表示するようにしようとしていますが、アプリがクラッシュします。

致命的な例外：メイン

 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

コード：

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);
}
javaandroidnullpointerexception
34
ryckiazai

アプリのクラッシュは次の場所にあります：

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

mPlayer=nullであるため。

PlayGameアクティビティでPlayer mPlayerを初期化するのを忘れました。

mPlayer = new Player(context,"");
50
M D