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我正在测试我的系统的hitboxes为我正在制作的游戏。问题是我在我的球类中出现以下错误： java.lang.NullPointerException：尝试在空对象引用ImageView未初始化
上调用虚拟方法'android.view.View android.view.Window.findViewById（int）'它发生在球类的构造函数方法的第一行。 有谁知道我是否做错了什么？
主类：
package xander.mazetestapp;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.RelativeLayout;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity implements SensorEventListener {
private TextView text;
private SensorManager sManager;
private int a = 300; //x position
private int b = 300; //y position
int x = 0;
int y = 0;
ball playingBall;
wall mazeWall;
float show = 1;
float hide = 0;
boolean allowedMovement[] = {true, true, true, true};
int maxX = 0;
int maxY = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = (TextView) findViewById(R.id.info);
sManager = (SensorManager) getSystemService(SENSOR_SERVICE);
playingBall = new ball();
mazeWall = new wall(hide, R.id.wall1);
}
//when this Activity starts
@Override
protected void onResume() {
super.onResume();
/*register the sensor listener to listen to the gyroscope sensor, use the
callbacks defined in this class, and gather the sensor information as quick
as possible*/
sManager.registerListener(this, sManager.getDefaultSensor(Sensor.TYPE_ORIENTATION), SensorManager.SENSOR_DELAY_FASTEST);
}
//When this Activity isn't visible anymore
@Override
protected void onStop() {
//unregister the sensor listener
sManager.unregisterListener(this);
super.onStop();
}
@Override
public void onAccuracyChanged(Sensor arg0, int arg1) {
//Do nothing.
}
public void limitMovement(ball ball, wall wall) {
float wy = (ball.getWidth() + wall.getWidth()) * (ball.getCenterY() - wall.getCenterY());
float hx = (ball.getHeight() + wall.getHeight()) * (ball.getCenterX() - wall.getCenterX());
if (wy > hx) {
if (wy > -hx) {//top
allowedMovement[1] = false;
} else {//left
allowedMovement[2] = false;
}
} else {
if (wy > -hx) {//right
allowedMovement[3] = false;
} else {//bottom
allowedMovement[0] = false;
}
}
}
public boolean intersect(ball ball, wall wall) {
//top left corner of the ball
if (ball.getTopLeftX() >= wall.getTopLeftX() && ball.getTopLeftX() <= wall.getTopRightX()) {
if (ball.getTopLeftY() >= wall.getTopLeftY() && ball.getTopLeftY() <= wall.getBottomLeftY()) {
limitMovement(ball, wall);
return true;
}
}
//top rigth corner of the ball
if (ball.getTopRightX() >= wall.getTopLeftX() && ball.getTopRightX() <= wall.getTopRightX()) {
if (ball.getTopRightY() >= wall.getTopLeftY() && ball.getTopRightY() <= wall.getBottomLeftY()) {
limitMovement(ball, wall);
return true;
}
}
//bottom left corner of the ball
if (ball.getBottomLeftX() >= wall.getBottomLeftX() && ball.getBottomLeftX() <= wall.getBottomRightX()) {
if (ball.getBottomLeftY() >= wall.getTopLeftY() && ball.getBottomLeftY() <= wall.getBottomLeftY()) {
limitMovement(ball, wall);
return true;
}
}
//bottom rigth corner of the ball
if (ball.getBottomRightX() >= wall.getBottomLeftX() && ball.getBottomRightX() <= wall.getBottomRightX()) {
if (ball.getBottomRightY() >= wall.getTopLeftY() && ball.getBottomRightY() <= wall.getBottomLeftY()) {
limitMovement(ball, wall);
return true;
}
}
return false;
}
public void move(int x, int y) {
RelativeLayout.LayoutParams alp = playingBall.getLayoutParams();
int maxMovementX = Math.abs(x);
int maxMovenentY = Math.abs(y);
int stepsTakenX = 0;
int stepsTakenY = 0;
while (maxMovementX > stepsTakenX || maxMovenentY > stepsTakenY) {
//up 0, down 1, right 3, left 2
if (stepsTakenX < maxMovementX) {
stepsTakenX = stepsTakenX + 1;
if (x > 0 && allowedMovement[3] == true) {//right
playingBall.setCenterX(playingBall.getCenterX() - 1);
a = a - 1;
}
if (x < 0 && allowedMovement[2] == true) {//left
playingBall.setCenterX(playingBall.getCenterX() + 1);
a = a + 1;
}
}
if (stepsTakenY < maxMovenentY) {
stepsTakenY = stepsTakenY + 1;
if (y > 0 && allowedMovement[1] == true) {//down
playingBall.setCenterY(playingBall.getCenterY() - 1);
b = b - 1;
}
if (y < 0 && allowedMovement[0] == true) {//up
playingBall.setCenterY(playingBall.getCenterY() + 1);
b = b + 1;
}
}
}
alp.leftMargin = a;
alp.topMargin = b;
playingBall.setLayoutParams(alp);
}
@Override
public void onSensorChanged(SensorEvent event) {
//if sensor is unreliable, return void
if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE) {
return;
}
//else it will output the Roll, Pitch and Yawn values
x = Math.round(event.values[2])/3;
y = Math.round(event.values[1])/3;
if (x > 15) {
x = 15;
}
if (x < -15) {
x = -15;
}
if (y > 15) {
y = 15;
}
if (y < -15) {
y = -15;
}
//kleinere x is naar links
//kleinere y is naar boven
//balk1 is boven
//balk2 is onder
//balk3 is links
//balk 4 is rechts
move(x, y);
text.setText("Width: " + playingBall.getWidth() +
" Height: " + playingBall.getHeight() +
" B x: " + playingBall.getCenterX() +
" B y: " + playingBall.getCenterY() +
" W x: " + mazeWall.getCenterX() +
" W y: " + mazeWall.getCenterY() +
" wall LB x: " + mazeWall.getTopLeftX() +
" wall LB y: " + mazeWall.getTopLeftY() +
"Width: " + mazeWall.getWidth() +
" Height: " + mazeWall.getHeight()
);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
球类：
package xander.mazetestapp;
import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;
import android.widget.RelativeLayout;
public class ball extends AppCompatActivity {
private int centerX;
private int centerY;
private int topLeftX;
private int topRightX;
private int bottomLeftX;
private int bottomRightX;
private int topLeftY;
private int topRightY;
private int bottomLeftY;
private int bottomRightY;
private int width;
private int height;
public ImageView ballImage;
public ball(){
ballImage = (ImageView) findViewById(R.id.ball);
centerX =(int) ballImage.getX();
centerY = (int) ballImage.getY();
width = ballImage.getWidth();
height = ballImage.getHeight();
setCorners();
}
private void setCorners() {
topLeftX=(centerX-(width/2));
topLeftY=(centerY-(height/2));
topRightX=(centerX+(width/2));
topRightY=(centerY-(height/2));
bottomRightX=(centerX+(width/2));
bottomRightY=(centerY+(height/2));
bottomLeftX=(centerX-(width/2));
bottomLeftY=(centerY+(height/2));
}
public int getWidth(){
return width;
}
public int getHeight(){
return height;
}
public int getCenterX(){
return centerX;
}
public int getCenterY(){
return centerY;
}
public int getTopLeftX(){
return topLeftX;
}
public int getTopRightX(){
return topRightX;
}
public int getBottomLeftX(){
return bottomLeftX;
}
public int getBottomRightX(){return bottomRightX;}
public int getTopLeftY(){
return topLeftY;
}
public int getTopRightY(){
return topRightY;
}
public int getBottomLeftY(){
return bottomLeftY;
}
public int getBottomRightY(){
return bottomRightY;
}
public void setCenterX(int x){
centerX=x;
}
public void setCenterY(int y){
centerY=y;
}
public RelativeLayout.LayoutParams getLayoutParams(){
return (RelativeLayout.LayoutParams) ballImage.getLayoutParams();
}
public void setLayoutParams(RelativeLayout.LayoutParams alp){
ballImage.setLayoutParams(alp);
}
球类活性，因此在初始化onCreate方法的ImageView –