Я использую зарезервированное слово?

Question

Я новичок в Android разработке и недавно начал курс по Udemy. Когда я пытался сделать простую игру, я столкнулся с проблемой при обращении к TextView.

Вот мой код для MainActivity. java:

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    int[] gameState = {2, 2, 2,
                       2, 2, 2,
                       2, 2, 2};

    int[][] winningPositions = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {0, 3, 6}, {1, 4, 7}, {2, 5, 8}, {0, 4, 8}, {2, 4, 6}};

    int activePlayer = 0;

    boolean gameActive = true;

    TextView hasWon = (TextView) findViewById(R.id.hasWon);

    Button playAgain = (Button) findViewById(R.id.playAgain);

    public void dropIn(View view) {

        ImageView counter = (ImageView) view;

        int tappedCounter = Integer.parseInt(counter.getTag().toString());

        if (gameState[tappedCounter] == 2 && gameActive) {

            gameState[tappedCounter] = activePlayer;

            counter.setTranslationY(-1500);

            if (activePlayer == 0) {

                counter.setImageResource(R.drawable.red);

                activePlayer = 1;

            } else {

                counter.setImageResource(R.drawable.yellow);

                activePlayer = 0;

            }

            counter.animate().translationYBy(1500).rotation(3600).setDuration(300);

            for (int[] winningPosition : winningPositions) {

                if (gameState[winningPosition[0]] == gameState[winningPosition[1]] && gameState[winningPosition[1]] == gameState[winningPosition[2]] && gameState[winningPosition[0]] != 2) {

                    String winner = "";

                    if (activePlayer == 1) {

                        winner = "Red";

                    } else {

                        winner = "Yellow";

                    }

                    Toast.makeText(this, winner + " has won!", Toast.LENGTH_LONG).show();

                    gameActive = false;

                }

            }

            if (!gameActive) {

                hasWon.setAlpha(1);

                playAgain.setAlpha(1);

                playAgain.setClickable(true);

            }

        } else {

            Toast.makeText(this, "No Fair!", Toast.LENGTH_SHORT).show();

        }

    }

    public void restartGame(View view) {

        gameState = new int[]{2, 2, 2, 2, 2, 2, 2, 2, 2};

        Toast.makeText(this, "Restarted!", Toast.LENGTH_SHORT).show();

    }

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

        hasWon.setAlpha(0);

        playAgain.setAlpha(0);

        playAgain.setClickable(true);

    }
}

здесь моя ошибка:

22396-22396/com.company321.connect3 E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.company321.connect3, PID: 22396
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.company321.connect3/com.company321.connect3.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
        at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:152)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:157)
        at android.content.Context.obtainStyledAttributes(Context.java:655)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:692)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:479)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214)
        at com.company321.connect3.MainActivity.<init>(MainActivity.java:25)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1174)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2669)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6494) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Она указывает на эту строку:

TextView hasWon = (TextView) findViewById(R.id.hasWon);

Пожалуйста, помогите мне решить эту проблему и скажите, что я делаю неправильно, и если я Я использую любые зарезервированные слова

Answer 1

Вот ваш код:

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    int[] gameState = {2, 2, 2,
                       2, 2, 2,
                       2, 2, 2};

    int[][] winningPositions = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {0, 3, 6}, {1, 4, 7}, {2, 5, 8}, {0, 4, 8}, {2, 4, 6}};

    int activePlayer = 0;

    boolean gameActive = true;
    TextView hasWon;
    Button playAgain;

    public void dropIn(View view) {

        ImageView counter = (ImageView) view;

        int tappedCounter = Integer.parseInt(counter.getTag().toString());

        if (gameState[tappedCounter] == 2 && gameActive) {

            gameState[tappedCounter] = activePlayer;

            counter.setTranslationY(-1500);

            if (activePlayer == 0) {

                counter.setImageResource(R.drawable.red);

                activePlayer = 1;

            } else {

                counter.setImageResource(R.drawable.yellow);

                activePlayer = 0;

            }

            counter.animate().translationYBy(1500).rotation(3600).setDuration(300);

            for (int[] winningPosition : winningPositions) {

                if (gameState[winningPosition[0]] == gameState[winningPosition[1]] && gameState[winningPosition[1]] == gameState[winningPosition[2]] && gameState[winningPosition[0]] != 2) {

                    String winner = "";

                    if (activePlayer == 1) {

                        winner = "Red";

                    } else {

                        winner = "Yellow";

                    }

                    Toast.makeText(this, winner + " has won!", Toast.LENGTH_LONG).show();

                    gameActive = false;

                }

            }

            if (!gameActive) {

                hasWon.setAlpha(1);

                playAgain.setAlpha(1);

                playAgain.setClickable(true);

            }

        } else {

            Toast.makeText(this, "No Fair!", Toast.LENGTH_SHORT).show();

        }

    }

    public void restartGame(View view) {

        gameState = new int[]{2, 2, 2, 2, 2, 2, 2, 2, 2};

        Toast.makeText(this, "Restarted!", Toast.LENGTH_SHORT).show();

    }

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

        hasWon = (TextView) findViewById(R.id.hasWon);
        playAgain = (Button) findViewById(R.id.playAgain);

        hasWon.setAlpha(0);

        playAgain.setAlpha(0);

        playAgain.setClickable(true);

    }
}

Answer 2

Проблема заключается в следующих строках:

    TextView hasWon = (TextView) findViewById(R.id.hasWon);

    Button playAgain = (Button) findViewById(R.id.playAgain);

Метод findViewById должен запускаться после setContentView в onCreate. Создание экземпляра класса происходит раньше, чем загрузка содержимого, поэтому возникает ошибка.