我得到一个nullpointer异常，并且不知道为什么。这是代码：
这是一个Tic Tac Toe游戏，但当我尝试为我的游戏上的按钮设置onClickListener时会抛出异常。
Mainactivity：
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
int board[][];
// button map
Button buttons[][];
int i, j;
TextView textView;
AI ai;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
init();
}
private boolean checkBoard() {
// is the game over?
boolean gameOver = false;
// first check all possible combinations to see if the user has won.
if ((board[1][1] == 0 && board[2][2] == 0 && board[3][3] == 0)
|| (board[1][3] == 0 && board[2][2] == 0 && board[3][1] == 0)
|| (board[1][2] == 0 && board[2][2] == 0 && board[3][2] == 0)
|| (board[1][3] == 0 && board[2][3] == 0 && board[3][3] == 0)
|| (board[1][1] == 0 && board[1][2] == 0 && board[1][3] == 0)
|| (board[2][1] == 0 && board[2][2] == 0 && board[2][3] == 0)
|| (board[3][1] == 0 && board[3][2] == 0 && board[3][3] == 0)
|| (board[1][1] == 0 && board[2][1] == 0 && board[3][1] == 0)) {
// user has won
textView.setText("You win!");
gameOver = true;
} else if ((board[1][1] == 1 && board[2][2] == 1 && board[3][3] == 1)
|| (board[1][3] == 1 && board[2][2] == 1 && board[3][1] == 1)
|| (board[1][2] == 1 && board[2][2] == 1 && board[3][2] == 1)
|| (board[1][3] == 1 && board[2][3] == 1 && board[3][3] == 1)
|| (board[1][1] == 1 && board[1][2] == 1 && board[1][3] == 1)
|| (board[2][1] == 1 && board[2][2] == 1 && board[2][3] == 1)
|| (board[3][1] == 1 && board[3][2] == 1 && board[3][3] == 1)
|| (board[1][1] == 1 && board[2][1] == 1 && board[3][1] == 1)) {
// computer has won
textView.setText("You lost!");
gameOver = true;
}
// Nobody has won but we still need to make sure that we have empty spaces
else {
boolean isEmpty = true;
for(i=1; i<=3; i++) {
for(j=1; j<=3; j++) {
if(board[i][j] == 2) {
isEmpty = false;
break;
}
}
}
if(isEmpty) {
gameOver = true;
textView.setText("It's a draw!");
}
}
return gameOver;
}
private class AI {
// the computer checks the board and takes its turn
public void takeTurn() {
try {
if (board[1][1] == 2 &&
((board[1][2] == 0 && board[1][3] == 0) ||
(board[2][2] == 0 && board[3][3] == 0) ||
(board[2][1] == 0 && board[3][1] == 0))) {
markSquare(1, 1);
} else if (board[1][2] == 2 &&
((board[2][2] == 0 && board[3][2] == 0) ||
(board[1][1] == 0 && board[1][3] == 0))) {
markSquare(1, 2);
} else if (board[1][3] == 2 &&
((board[1][1] == 0 && board[1][2] == 0) ||
(board[3][1] == 0 && board[2][2] == 0) ||
(board[2][3] == 0 && board[3][3] == 0))) {
markSquare(1, 3);
} else if (board[2][1] == 2 &&
((board[2][2] == 0 && board[2][3] == 0) ||
(board[1][1] == 0 && board[3][1] == 0))) {
markSquare(2, 1);
} else if (board[2][2] == 2 &&
((board[1][1] == 0 && board[3][3] == 0) ||
(board[1][2] == 0 && board[3][2] == 0) ||
(board[3][1] == 0 && board[1][3] == 0) ||
(board[2][1] == 0 && board[2][3] == 0))) {
markSquare(2, 2);
} else if (board[2][3] == 2 &&
((board[2][1] == 0 && board[2][2] == 0) ||
(board[1][3] == 0 && board[3][3] == 0))) {
markSquare(2, 3);
} else if (board[3][1] == 2 &&
((board[1][1] == 0 && board[2][1] == 0) ||
(board[3][2] == 0 && board[3][3] == 0) ||
(board[2][2] == 0 && board[1][3] == 0))) {
markSquare(3, 1);
} else if (board[3][2] == 2 &&
((board[1][2] == 0 && board[2][2] == 0) ||
(board[3][1] == 0 && board[3][3] == 0))) {
markSquare(3, 2);
} else if (board[3][3] == 2 &&
((board[1][1] == 0 && board[2][2] == 0) ||
(board[1][3] == 0 && board[2][3] == 0) ||
(board[3][1] == 0 && board[3][2] == 0))) {
markSquare(3, 3);
}
// There is nothing to block so choose a random square
else {
Random rand = new Random();
int a = rand.nextInt(4);
int b = rand.nextInt(4);
while (a == 0 || b == 0 || board[a][b] != 2) {
a = rand.nextInt(4);
b = rand.nextInt(4);
}
markSquare(a, b);
}
}catch (Exception e) {
e.printStackTrace();
}
}
// Mark the selected square
private void markSquare(int x, int y) {
buttons[x][y].setEnabled(false);
buttons[x][y].setText("X");
board[x][y] = 1;
checkBoard();
}
}
class ClickListener implements View.OnClickListener {
// this buttons position in the arrays
int x;
int y;
public ClickListener(int x, int y) {
this.x = x;
this.y = y;
}
// handle the click event
public void onClick(View view) {
// check to see if the button is enabled
if(buttons[x][y].isEnabled()) {
buttons[x][y].setEnabled(false);
// mark it as belonging to the user
buttons[x][y].setText("O");
board[x][y] = 0;
// check to see if the user has won, if not let AI take turn
if(!checkBoard()) {
ai.takeTurn();
}
}
}
}
private void init() {
ai = new AI();
buttons = new Button[4][4];
board = new int[4][4];
// get the objects defined in main.xml
textView = (TextView) findViewById(R.id.dialogue);
buttons[1][3] = (Button) findViewById(R.id.one);
buttons[1][2] = (Button) findViewById(R.id.two);
buttons[1][1] = (Button) findViewById(R.id.three);
buttons[2][3] = (Button) findViewById(R.id.four);
buttons[2][2] = (Button) findViewById(R.id.five);
buttons[2][1] = (Button) findViewById(R.id.six);
buttons[3][3] = (Button) findViewById(R.id.seven);
buttons[3][2] = (Button) findViewById(R.id.eight);
buttons[3][1] = (Button) findViewById(R.id.nine);
// set the values of the board to 2 (empty)
for (i = 1; i <= 3; i++) {
for (j = 1; j <= 3; j++)
board[i][j] = 2;
}
// add the click listeners for each button
for (i = 1; i <= 3; i++) {
for (j = 1; j <= 3; j++) {
buttons[i][j].setOnClickListener(new ClickListener(i, j));
if(!buttons[i][j].isEnabled()) {
buttons[i][j].setText(" ");
buttons[i][j].setEnabled(true);
}
}
}
}
}
布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="azval.tictactoe.MainActivity">
<Button android:id="@+id/one"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_alignParentTop="true" android:layout_toRightOf="@+id/two" android:layout_toEndOf="@+id/two"/>
<Button android:id="@+id/two"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_alignParentTop="true" android:layout_toRightOf="@+id/three"
android:layout_toEndOf="@+id/three"/>
<Button android:id="@+id/three"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:padding="0px"
android:layout_alignTop="@+id/two"
android:layout_alignStart="@+id/six" />
<Button android:id="@+id/four"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/one" android:layout_toRightOf="@+id/two"/>
<Button android:id="@+id/five"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/two" android:layout_toRightOf="@+id/three"/>
<Button android:id="@+id/six"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/three"
android:layout_alignParentLeft="true"
android:layout_marginLeft="61dp" />
<Button android:id="@+id/seven"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/four" android:layout_toRightOf="@+id/two"/>
<Button android:id="@+id/eight"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/five" android:layout_toRightOf="@+id/three"/>
<Button android:id="@+id/nine"
android:layout_width="75dp"
android:layout_height="75dp"
android:text=" "
android:textSize="70px"
android:layout_below="@+id/six"
android:layout_alignParentLeft="true"
android:layout_marginLeft="61dp" />
<TextView android:id="@+id/dialogue"
android:layout_width="fill_parent"
android:layout_below="@id/nine"
android:layout_height="wrap_content"
android:text="Click a button to start"
android:gravity="center_horizontal"
android:layout_marginTop="10dp"
android:textSize="15sp"/>
</RelativeLayout>
答案 0 :(得分：0)
在活动的视图层次结构中找到视图之前，您实际上需要将一些内容传递给活动。在setContentView(R.layout.your_activity_layout)之前致电init()。