android - Android Studio：尝试在空对象上调用虚拟方法“void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)”
问题描述
请任何帮助???
确实存在与我要问的问题类似的问题，但是我确实尝试了您提出的所有解决方案，但对我不起作用。
我在控制台中遇到的错误。
E/AndroidRuntime: 致命异常: main
Process: ems.develop.megagame3, PID: 9574
java.lang.RuntimeException: Unable to start activity ComponentInfo{ems.develop.megagame3/ems.develop.megagame3.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
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 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at ems.develop.megagame3.MainActivity.onCreate(MainActivity.java:41)
at android.app.Activity.performCreate(Activity.java:7009)
at android.app.Activity.performCreate(Activity.java:7000)
#
这里是 mainActivity.java
public class MainActivity extends AppCompatActivity {
private EditText TxtNumber=null ;
private Button lblCompare;
private TextView TxtResult;
private ProgressBar pgbScole;
private TextView TxtHistory;
private int searchedValue;
private int score;
public MainActivity() {
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/* TxtNumber =(EditText) findViewById(R.id.TxtNumber); */
TxtNumber =(EditText) findViewById(R.id.TxtNumber);
lblCompare =(Button) findViewById(R.id.lblCompare);
TxtResult =(TextView) findViewById(R.id.TxtResult);
pgbScole =(ProgressBar) findViewById(R.id.pgbScole);
TxtHistory= (TextView) findViewById(R.id.TxtHistory);
lblCompare.setOnClickListener(btnCompareListner);
init();
}
private void init() {
score= 0;
searchedValue = 1+ (int)(Math.random() *100);
Log.i("DEBUG", " Valeur cherché "+searchedValue);
// réinitialisation des fields
TxtNumber.setText("");
pgbScole.setProgress(score);
TxtResult.setText("");
TxtHistory.setText("");
// Mettre le focus au field TxtNumber;
TxtNumber.requestFocus();
}
private View.OnClickListener btnCompareListner;
{
btnCompareListner = new View.OnClickListener() {
@Override
public void onClick(View view) {
Log.i("Debug", "Bouton cliqué ");
String txtNumber = TxtNumber.getText().toString();
if (txtNumber.equals("")) return;
TxtHistory.append(TxtNumber +"\r\n");
pgbScole.incrementProgressBy(1);
score++;
int enteredValue = Integer.parseInt(txtNumber);
if (enteredValue == searchedValue) {
congratulations();
} else if (enteredValue < searchedValue) {
TxtResult.setText(R.string.strGreater);
}else{
TxtResult.setText(R.string.strLower);
}
TxtNumber.setText("");
TxtNumber.requestFocus();
}
};
}
private void congratulations() {
TxtResult.setText(R.string.congra);
AlertDialog retryAlert= new AlertDialog.Builder(this).create();
retryAlert.setTitle(R.string.app_name);
retryAlert.setMessage(getString( R.string.strMessage,score));
retryAlert.setButton(AlertDialog.BUTTON_POSITIVE, getString(R.string.strYes), new AlertDialog.OnClickListener(){
@Override
public void onClick(DialogInterface dialogInterface, int i) {
init();
}
});
retryAlert.setButton(AlertDialog.BUTTON_NEGATIVE, getString(R.string.strNo), new AlertDialog.OnClickListener(){
@Override
public void onClick(DialogInterface dialogInterface, int i) {
finish();
}
});
retryAlert.show();
}
这是“activity_main.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="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<android.support.constraint.Guideline
android:id="@+id/guideline3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="281dp"
android:orientation="vertical"
app:layout_constraintBottom_toTopOf="@+id/pgbScole"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintGuide_end="-44dp"
app:layout_constraintTop_toTopOf="parent">
<ProgressBar
android:id="@+id/pgbScole"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="448dp"
android:layout_height="14dp"
android:layout_marginTop="180dp"
android:max="10"
android:progress="5"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.68"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/lbltitre"
style="@android:style/Animation"
android:layout_width="0dp"
android:layout_height="42dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="29dp"
android:layout_marginLeft="29dp"
android:layout_marginRight="29dp"
android:layout_marginStart="29dp"
android:text="@string/lblTitle"
android:textAppearance="@android:style/TextAppearance.Large"
android:textColor="@android:color/background_dark"
android:textColorHighlight="@android:color/background_dark"
android:textColorHint="@android:color/background_dark"
android:textColorLink="@android:color/holo_purple"
app:layout_constraintBottom_toTopOf="@+id/TxtNumber"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0"
tools:height="?android:attr/lightRadius"
tools:textCursorDrawable="@android:color/holo_blue_dark"
tools:textSize="18sp" />
<EditText
android:id="@+id/TxtNumber"
android:layout_width="0dp"
android:layout_height="43dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginLeft="28dp"
android:layout_marginRight="8dp"
android:layout_marginStart="28dp"
android:layout_marginTop="56dp"
android:ems="10"
android:inputType="numberSigned"
app:layout_constraintBottom_toTopOf="@+id/TxtResult"
app:layout_constraintEnd_toStartOf="@+id/lblCompare"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:ignore="UnknownId" />
<Button
android:id="@+id/lblCompare"
android:layout_width="159dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="28dp"
android:layout_marginRight="28dp"
android:layout_marginTop="64dp"
android:text="@string/lblComapre"
app:layout_constraintBottom_toBottomOf="@+id/TxtResult"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.036" />
<TextView
android:id="@+id/TxtHistory"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="24dp"
android:layout_marginEnd="12dp"
android:layout_marginLeft="12dp"
android:layout_marginRight="12dp"
android:layout_marginStart="12dp"
android:layout_marginTop="8dp"
android:background="@color/colorAccent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/pgbScole" />
<EditText
android:id="@+id/TxtResult"
android:layout_width="299dp"
android:layout_height="47dp"
android:layout_marginBottom="4dp"
android:layout_marginEnd="56dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="56dp"
android:layout_marginStart="8dp"
android:ems="10"
android:inputType="textPersonName"
app:layout_constraintBottom_toTopOf="@+id/pgbScole"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="@+id/guideline3" />
</android.support.constraint.Guideline>
解决方案
确保您没有其他xml同名的，并且您正在使用这个 another xml。
一个非常相似的场景是，当您有两种不同配置的布局时，例如，landscape一个portrait有views而另一个没有
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