A
androidcoder
Neues Mitglied
- 0
Hallo,
ich bin noch Anfänger und hoffe, dass ihr für diese Frage Verständnis habt.
Warum bekomme ich hier eine NullPointerException?
Ich weiß, es ligt an dieser Zeile Code
button = (Button) findViewById(R.id.buttn);
aber ich verstehe nicht, warum es wegen diesem Code zu einer NullPointerException kommt?
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
ich bin noch Anfänger und hoffe, dass ihr für diese Frage Verständnis habt.
Warum bekomme ich hier eine NullPointerException?
Ich weiß, es ligt an dieser Zeile Code
button = (Button) findViewById(R.id.buttn);
aber ich verstehe nicht, warum es wegen diesem Code zu einer NullPointerException kommt?
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
Code:
public class MainActivity extends AppCompatActivity {
private EditText userInput;
private TextView textView;
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
userInput = (EditText) findViewById(R.id.editText);
textView = (TextView) findViewById(R.id.textView);
button = (Button) findViewById(R.id.buttn);
textView.setText("");
textView.setMovementMethod(new ScrollingMovementMethod());
View.OnClickListener ourOnClickListener = new View.OnClickListener(){
@Override
public void onClick(View view){
textView.getText();
String result = userInput.getText() +"\n";
textView.append(result);
}
};
button.setOnClickListener(ourOnClickListener);
}
}
Code:
<?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:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.timbuchalka.buttonclickcounter.MainActivity">
<Button
android:id="@+id/button"
android:layout_width="93dp"
android:layout_height="53dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:layout_marginTop="16dp"
android:text="Button"
app:layout_constraintRight_toRightOf="@+id/activity_main"
app:layout_constraintTop_toTopOf="@+id/activity_main" />
<EditText
android:id="@+id/editText"
android:layout_width="0dp"
android:layout_height="42dp"
android:layout_marginEnd="16dp"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:ems="10"
android:inputType="textPersonName"
android:text="Name"
app:layout_constraintHorizontal_bias="0.4"
app:layout_constraintLeft_toLeftOf="@+id/activity_main"
app:layout_constraintRight_toLeftOf="@+id/button"
app:layout_constraintTop_toTopOf="@+id/activity_main" />
<TextView
android:id="@+id/textView"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginBottom="16dp"
android:layout_marginEnd="16dp"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:scrollIndicators="right|end"
android:scrollbars="vertical"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="@+id/activity_main"
app:layout_constraintLeft_toLeftOf="@+id/activity_main"
app:layout_constraintRight_toRightOf="@+id/activity_main"
app:layout_constraintTop_toBottomOf="@+id/editText"
app:layout_constraintVertical_bias="0.0" />
</android.support.constraint.ConstraintLayout>
Code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="1">
<Button
android:id="@+id/buttn"
android:layout_width="209dp"
android:layout_height="17dp"
android:layout_weight="0.08"
android:text="Button" />
</LinearLayout>