我为tictactoe游戏编写了一个代码，但是它在运行时显示了这个错误：
Exception: Unable to instantiate activity ComponentInfo{com.tictactoe.ajaykulkarni.tictactoe/com.tictactoe.ajaykulkarni.tictactoe.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Bundle android.content.Intent.getExtras()' on a null object reference
我的MainActivity是：
package com.tictactoe.ajaykulkarni.tictactoe;
import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.util.Log;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.Window;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
//protected DrawerLayout mdrawerLayout;
/*Game plan*/
private TicTacToeGame mGame;
// Buttons making up the board
private Button mBoardButtons[];
private Button mNewGame;
// Various text displayed
private TextView mInfoTextView;
private TextView mPlayerOneCount;
private TextView mTieCount;
private TextView mPlayerTwoCount;
private TextView mPlayerOneText;
private TextView mPlayerTwoText;
private int mPlayerOneCounter = 0;
private int mTieCounter = 0;
private int mPlayerTwoCounter = 0;
private boolean mPlayerOneFirst = true;
private boolean mIsSinglePlayer = false;
private boolean mIsPlayerOneTurn = true;
private boolean mGameOver = false;
boolean mGameType = getIntent().getExtras().getBoolean("gameType");
private Button[] getmBoardButtons() {
mBoardButtons = new Button[mGame.getBOARD_SIZE()];
mBoardButtons[0] = (Button) findViewById(R.id.one);
mBoardButtons[1] = (Button) findViewById(R.id.two);
mBoardButtons[2] = (Button) findViewById(R.id.three);
mBoardButtons[3] = (Button) findViewById(R.id.four);
mBoardButtons[4] = (Button) findViewById(R.id.five);
mBoardButtons[5] = (Button) findViewById(R.id.six);
mBoardButtons[6] = (Button) findViewById(R.id.seven);
mBoardButtons[7] = (Button) findViewById(R.id.eight);
mBoardButtons[8] = (Button) findViewById(R.id.nine);
addListenerOnButton();
// setup the textviews
mInfoTextView = (TextView) findViewById(R.id.information);
mPlayerOneCount = (TextView) findViewById(R.id.humanCount);
mTieCount = (TextView) findViewById(R.id.tiesCount);
mPlayerTwoCount = (TextView) findViewById(R.id.androidCount);
mPlayerOneText = (TextView) findViewById(R.id.human);
mPlayerTwoText = (TextView) findViewById(R.id.android);
// set the initial counter display values
mPlayerOneCount.setText(Integer.toString(mPlayerOneCounter));
mTieCount.setText(Integer.toString(mTieCounter));
mPlayerTwoCount.setText(Integer.toString(mPlayerTwoCounter));
// create a new game object
mGame = new TicTacToeGame();
// start a new game
startNewGame(mGameType);
return mBoardButtons;
}
//mBoardButtons = new Button[mGame.getBOARD_SIZE()];
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.play) {
Log.d("DEBUG", "Play option selected!");
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
} else if (id == R.id.exit) {
Log.d("DEBUG", "Exit option selected!");
MainActivity.this.finish();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
public void addListenerOnButton(){
mNewGame = (Button) findViewById(R.id.NewGame);
mNewGame.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
startNewGame(mIsSinglePlayer);
}
});
}
// start a new game
// clears the board and resets all buttons / text
// sets game over to be false
private void startNewGame(boolean isSingle)
{
this.mIsSinglePlayer = isSingle;
mGame.clearBoard();
for (int i = 0; i < mBoardButtons.length; i++)
{
mBoardButtons[i].setText("");
mBoardButtons[i].setEnabled(true);
mBoardButtons[i].setOnClickListener(new ButtonClickListener(i));
///mBoardButtons[i].setBackgroundDrawable(getResources().getDrawable(R.drawable.blank));
}
if (mIsSinglePlayer)
{
mPlayerOneText.setText("User:");
mPlayerTwoText.setText("Android:");
if (mPlayerOneFirst)
{
mInfoTextView.setText(R.string.first_human);
mPlayerOneFirst = false;
}
else
{
mInfoTextView.setText(R.string.turn_computer);
int move = mGame.getComputerMove();
setMove(mGame.PLAYER_TWO, move);
mPlayerOneFirst = true;
}
}
mGameOver = false;
}
private class ButtonClickListener implements View.OnClickListener
{
int location;
public ButtonClickListener(int location)
{
this.location = location;
}
public void onClick(View view)
{
if (!mGameOver)
{
if (mBoardButtons[location].isEnabled())
{
if (mIsSinglePlayer)
{
setMove(mGame.PLAYER_ONE, location);
int winner = mGame.checkForWinner();
if (winner == 0)
{
mInfoTextView.setText(R.string.turn_computer);
int move = mGame.getComputerMove();
setMove(mGame.PLAYER_TWO, move);
winner = mGame.checkForWinner();
}
if (winner == 0)
mInfoTextView.setText(R.string.turn_human);
else if (winner == 1)
{
mInfoTextView.setText(R.string.result_tie);
mTieCounter++;
mTieCount.setText(Integer.toString(mTieCounter));
mGameOver = true;
}
else if (winner == 2)
{
mInfoTextView.setText(R.string.result_human_wins);
mPlayerOneCounter++;
mPlayerOneCount.setText(Integer.toString(mPlayerOneCounter));
mGameOver = true;
}
else
{
mInfoTextView.setText(R.string.result_android_wins);
mPlayerTwoCounter++;
mPlayerTwoCount.setText(Integer.toString(mPlayerTwoCounter));
mGameOver = true;
}
}
else
{
if (mIsPlayerOneTurn)
setMove(mGame.PLAYER_ONE, location);
else
setMove(mGame.PLAYER_TWO, location);
int winner = mGame.checkForWinner();
if (winner == 0)
{
if (mIsPlayerOneTurn)
{
mInfoTextView.setText(R.string.turn_player_two);
mIsPlayerOneTurn = false;
}
else
{
mInfoTextView.setText(R.string.turn_player_one);
mIsPlayerOneTurn = true;
}
}
else if (winner == 1)
{
mInfoTextView.setText(R.string.result_tie);
mTieCounter++;
mTieCount.setText(Integer.toString(mTieCounter));
mGameOver = true;
}
else if (winner == 2)
{
mInfoTextView.setText(R.string.result_player_one_wins);
mPlayerOneCounter++;
mPlayerOneCount.setText(Integer.toString(mPlayerOneCounter));
mGameOver = true;
mIsPlayerOneTurn = false;
}
else
{
mInfoTextView.setText(R.string.result_player_two_wins);
mPlayerTwoCounter++;
mPlayerTwoCount.setText(Integer.toString(mPlayerTwoCounter));
mGameOver = true;
mIsPlayerOneTurn = true;
}
}
}
}
}
}
// set move for the current player
private void setMove(char player, int location)
{
mGame.setMove(player, location);
mBoardButtons[location].setEnabled(false);
if (player == mGame.PLAYER_ONE)
mBoardButtons[location].setBackgroundDrawable(getResources().getDrawable(R.drawable.ic_x));
else
mBoardButtons[location].setBackgroundDrawable(getResources().getDrawable(R.drawable.ic_o));
}
}
和TicTacToeGame.class是：
package com.tictactoe.ajaykulkarni.tictactoe;
/**
* Created by Ajay Kulkarni-enEXL on 02/16/2017.
*/
import java.util.Random;
public class TicTacToeGame {
private char mBoard[];
private final static int BOARD_SIZE = 9;
public static final char PLAYER_ONE = 'X';
public static final char PLAYER_TWO = '0';
public static final char EMPTY_SPACE = ' ';
private Random mRand;
public static int getBOARD_SIZE() {
// Return the size of the board
return BOARD_SIZE;
}
public TicTacToeGame(){
mBoard = new char[BOARD_SIZE];
for (int i = 0; i < BOARD_SIZE; i++)
mBoard[i] = EMPTY_SPACE;
mRand = new Random();
}
// Clear the board of all X's and O's
public void clearBoard()
{
for (int i = 0; i < BOARD_SIZE; i++)
{
mBoard[i] = EMPTY_SPACE;
}
}
// set the given player at the given location on the game board.
// the location must be available, or the board will not be changed.
public void setMove(char player, int location)
{
mBoard[location] = player;
}
// Return the best move for the computer to make. You must call setMove()
// to actually make the computer move to that location.
public int getComputerMove()
{
int move;
// First see if there's a move O can make to win
for (int i = 0; i < getBOARD_SIZE(); i++)
{
if (mBoard[i] != PLAYER_ONE && mBoard[i] != PLAYER_TWO)
{
char curr = mBoard[i];
mBoard[i] = PLAYER_TWO;
if (checkForWinner() == 3)
{
setMove(PLAYER_TWO, i);
return i;
}
else
mBoard[i] = curr;
}
}
// See if there's a move O can make to block X from winning
for (int i = 0; i < getBOARD_SIZE(); i++)
{
if (mBoard[i] != PLAYER_ONE && mBoard[i] != PLAYER_TWO)
{
char curr = mBoard[i];
mBoard[i] = PLAYER_ONE;
if (checkForWinner() == 2)
{
setMove(PLAYER_TWO, i);
return i;
}
else
mBoard[i] = curr;
}
}
// Generate random move
do
{
move = mRand.nextInt(getBOARD_SIZE());
} while (mBoard[move] == PLAYER_ONE || mBoard[move] == PLAYER_TWO);
setMove(PLAYER_TWO, move);
return move;
}
// Check for a winner and return a status value indicating who has won.
// Return 0 if no winner or tie yet, 1 if it's a tie, 2 if X won, or 3
// if O won.
public int checkForWinner()
{
// Check horizontal wins
for (int i = 0; i <= 6; i += 3)
{
if (mBoard[i] == PLAYER_ONE &&
mBoard[i+1] == PLAYER_ONE &&
mBoard[i+2] == PLAYER_ONE)
return 2;
if (mBoard[i] == PLAYER_TWO &&
mBoard[i+1] == PLAYER_TWO &&
mBoard[i+2] == PLAYER_TWO)
return 3;
}
// Check vertical wins
for (int i = 0; i <= 2; i++)
{
if (mBoard[i] == PLAYER_ONE &&
mBoard[i+3] == PLAYER_ONE &&
mBoard[i+6] == PLAYER_ONE)
return 2;
if (mBoard[i] == PLAYER_TWO &&
mBoard[i+3] == PLAYER_TWO &&
mBoard[i+6] == PLAYER_TWO)
return 3;
}
// Check for diagonal wins
if ((mBoard[0] == PLAYER_ONE &&
mBoard[4] == PLAYER_ONE &&
mBoard[8] == PLAYER_ONE) ||
mBoard[2] == PLAYER_ONE &&
mBoard[4] == PLAYER_ONE &&
mBoard[6] == PLAYER_ONE)
return 2;
if ((mBoard[0] == PLAYER_TWO &&
mBoard[4] == PLAYER_TWO &&
mBoard[8] == PLAYER_TWO) ||
mBoard[2] == PLAYER_TWO &&
mBoard[4] == PLAYER_TWO &&
mBoard[6] == PLAYER_TWO)
return 3;
// Check for a tie
for (int i = 0; i < getBOARD_SIZE(); i++)
{
// if we find a number, then no one has won yet
if (mBoard[i] != PLAYER_ONE && mBoard[i] != PLAYER_TWO)
return 0;
}
// If we make it through the previous loop, all places are taken, so it's a tie
return 1;
}
}
如何修复该错误？
答案 0 :(得分：3)
您正在尝试从活动中的字段中获取额外内容，即您正在尝试在创建活动之前获取额外内容。如果您从 onCreate 方法获得额外内容，则它不会是空值。
示例：
="Date To"编辑：如果你想从一个活动向另一个活动发送额外的活动，你应该这样开始：
boolean mGameType;
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mGameType = getIntent().getExtras().getBoolean("gameType");
...
}