我的代码有问题。 我在Android Studio上工作，当我启动代码时，出现此错误：
java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.TextView.setText（java.lang.CharSequence）'
我在很多网站上搜索，但找不到任何答复。
这是我的代码：
我的活动Action.java：
public class Action extends AppCompatActivity {
private TextView nbDef;
private TextView printPlayer;
private final List<String> name = new Vector<>();
private final HashMap<String, Integer> score = new HashMap<>();
private String mode;
private int nbAllTurn;
private String TurnPlayer;
private int nbTurn = 0;
private int idPlayer = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_action);
this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
nbDef = findViewById(R.id.number);
printPlayer = findViewById(R.id.challenge);
nbDef.setText("0/" + nbAllTurn);
Intent intent = getIntent();
mode = intent.getStringExtra("mode");
nbAllTurn = intent.getIntExtra("nbTurn", -1);
String player = intent.getStringExtra("players");
String[] rawPlayers = player.split("\n");
for (String rawPlayer : rawPlayers) {
name.add(rawPlayer);
score.put(rawPlayer, 0);
}
DoAction();
}
private void DoAction() {
List<String> OtherPlayers = new Vector<>();
TurnPlayer = name.get(idPlayer);
for (int index = 0; index < name.size(); index++) {
if (!name.get(index).equals(TurnPlayer))
OtherPlayers.add(name.get(index));
}
printPlayer.setText(TurnPlayer);
List<String> challenges = new ArrayList<>();
challenges.add(", raconte une anecdote gênante sur ");
challenges.add(", fais un chifoumi avec ");
challenges.add(", raconte une histoire chiante sur ");
challenges.add(", mange des chaussettes avec ");
String choosePlayer = OtherPlayers.get(new Random().nextInt(OtherPlayers.size()));
String chooseChallenge = challenges.get(new Random().nextInt(challenges.size()));
String playerAction = printPlayer.getText().toString() + chooseChallenge;
printPlayer.setText(playerAction);
String playersAction = printPlayer.getText().toString() + choosePlayer;
printPlayer.setText(playersAction);
String challengeNum = Integer.toString(nbTurn) + "/" + Integer.toString(nbAllTurn);
nbDef.setText(challengeNum);
idPlayer += 1;
if (idPlayer == name.size()) {
idPlayer = 0;
}
nbTurn +=1;
if (nbTurn == nbAllTurn) {
StringBuilder builder = new StringBuilder();
for (String name : score.keySet()) {
builder.append(name).append(" : ").append(score.get(name)).append("\n");
}
Intent intent = new Intent(this, ScoreBoard.class);
intent.putExtra("datas", builder.toString());
startActivity(intent);
finish();
}
}
public void successClick(View v) {
DoAction();
score.put(TurnPlayer, score.get(TurnPlayer) + 1);
}
public void failClick(View v) {
DoAction();
}
}
错误出现在nbDef.setText行的onCreate方法中。
这是XML文件：activity_action.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@color/body_action_back"
tools:context=".Action"
tools:layout_editor_absoluteY="25dp">
<TextView
android:id="@+id/challenge"
android:layout_width="0dp"
android:layout_height="127dp"
android:layout_marginEnd="56dp"
android:textAlignment="center"
android:textColor="@color/colorPrimaryDark"
android:textSize="24sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/imageView2"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.373"
tools:maxLines="5" />
<ImageView
android:id="@+id/imageView2"
android:layout_width="0dp"
android:layout_height="172dp"
android:layout_marginStart="69dp"
android:contentDescription="@string/cartoon"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="@+id/challenge"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.334"
app:srcCompat="@drawable/pikachu" />
<!--<RelativeLayout
android:id="@+id/relativeLayout"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="11dp"
app:layout_constraintEnd_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
</RelativeLayout>-->
<ImageButton
android:id="@+id/success_button"
android:layout_width="186dp"
android:layout_height="68dp"
android:layout_marginStart="144dp"
android:layout_marginTop="53dp"
android:layout_marginEnd="59dp"
android:layout_marginBottom="38dp"
android:onClick="successClick"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="@+id/fail_button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/imageView2"
app:srcCompat="@drawable/successbutton" />
<ImageButton
android:id="@+id/fail_button"
android:layout_width="186dp"
android:layout_height="68dp"
android:layout_marginStart="59dp"
android:layout_marginTop="72dp"
android:layout_marginEnd="156dp"
android:layout_marginBottom="38dp"
android:onClick="failClick"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/success_button"
app:layout_constraintTop_toBottomOf="@+id/challenge"
app:srcCompat="@drawable/failbutton" />
<TextView
android:id="@+id/number"
android:layout_width="88dp"
android:layout_height="53dp"
android:layout_marginStart="41dp"
android:layout_marginTop="119dp"
android:layout_marginEnd="7dp"
android:layout_marginBottom="7dp"
android:textAlignment="center"
android:textColor="@color/colorPrimaryDark"
android:textSize="24sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/fail_button"
app:layout_constraintTop_toBottomOf="@+id/challenge"
tools:maxLines="5"/>
</android.support.constraint.ConstraintLayout>
失败的TextView是最后一个以id为ID的数字。
我知道什么是NullPointerException，但我不明白为什么它会失败，因为a使用printPlayer TextView进行了完全相同的操作，并且没有失败。
非常感谢您能给我的帮助！
答案 0 :(得分：0)
我认为您正在获得NPE
nbDef = findViewById(R.id.number);
如果传递有效的id，则findViewById返回null的唯一原因是您设置了错误的内容视图（使用setContentView）