Why doesn't try-Catch work as it's supposed to be?

Question

I wanted to make a try-catch block.

In my try block there's a method which checks if a radioButton is pressed, if so it should set an enum and go forward and if no radioButton is pressed, a NullPointerException should be thrown and the app closes (there're coming some extra features which aren't finished yet so I removed them for now).

Everything I saw so far didnt fit to my problem because they just forgot a catch or they missspelled a method or something like this.

It works if I don't press a radioButton my app closes, but if I press one radioButton my app closes again, but it should go to my next layout and set an enum (depending on which radioButton is pressed.

My java-code:

   public void setKnowledge() {
    setContentView(R.layout.knowledge_level);

    Button checking = (Button) findViewById(R.id.buttonChecking);

    checking.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            try {
                checkSelection();
                setContentView(R.layout.category_auswahl);
            }catch(NullPointerException n) {
                android.os.Process.killProcess(android.os.Process.myPid());
                System.exit(0);
            }
        }
    });
}

public knowledge checkSelection() {
    RadioButton rbNoob = (RadioButton) findViewById(R.id.radioButtonNoob);
    RadioButton rbBeginner = (RadioButton) findViewById(R.id.radioButtonBeginner);
    RadioButton rbAdvanced = (RadioButton) findViewById(R.id.radioButtonAdv);
    RadioButton rbPro = (RadioButton) findViewById(R.id.radioButtonPro);
    RadioButton rbGrandMaster = (RadioButton) findViewById(R.id.radioButtonGM);

    advertisment();

    if(rbNoob.isChecked()) {
        return knowledge.NOOB;
    }
    else if(rbBeginner.isChecked()) {
        return knowledge.BEGINNER;
    }
    else if(rbAdvanced.isChecked()) {
        return knowledge.ADVANCED;
    }
    else if(rbPro.isChecked()) {
        return knowledge.PRO;
    }
    else if(rbGrandMaster.isChecked()) {
        return knowledge.GM;
    }
    return null;
}

My XML: (EDIT: knowledge_level.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"
android:background="#081929" >

<RadioGroup
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="32dp"
    app:layout_constraintTop_toBottomOf="@+id/testWissenstandText"
    android:layout_marginLeft="8dp"
    app:layout_constraintLeft_toLeftOf="parent"
    android:id="@+id/radioGroup"
    app:layout_constraintRight_toLeftOf="@+id/buttonChecking"
    android:layout_marginRight="8dp"
    app:layout_constraintHorizontal_bias="0.538">

    <RadioButton
        android:id="@+id/radioButtonNoob"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_marginTop="8dp"
        android:checked="false"
        android:text="Keine Vorkenntnisse"
        android:textAlignment="center"
        android:textColor="#E0E0E0"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.505"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/buttonChecking"
        app:layout_constraintTop_toBottomOf="@+id/testWissenstandText"/>

    <RadioButton
        android:id="@+id/radioButtonBeginner"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_marginTop="8dp"
        android:checked="false"
        android:text="Anfänger"
        android:textAlignment="center"
        android:textColor="#E0E0E0"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="@+id/radioButtonNoob"
        app:layout_constraintRight_toRightOf="@+id/radioButtonNoob"
        app:layout_constraintTop_toBottomOf="@+id/radioButtonNoob"/>

    <RadioButton
        android:id="@+id/radioButtonAdv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_marginTop="8dp"
        android:text="Fortgeschrittener"
        android:textAlignment="center"
        android:textColor="#E0E0E0"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="@+id/radioButtonBeginner"
        app:layout_constraintRight_toRightOf="@+id/radioButtonBeginner"
        app:layout_constraintTop_toBottomOf="@+id/radioButtonBeginner"/>

    <RadioButton
        android:id="@+id/radioButtonPro"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_marginTop="8dp"
        android:text="Pro"
        android:textAlignment="center"
        android:textColor="#E0E0E0"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="@+id/radioButtonAdv"
        app:layout_constraintRight_toRightOf="@+id/radioButtonAdv"
        app:layout_constraintTop_toBottomOf="@+id/radioButtonAdv"/>

    <RadioButton
        android:id="@+id/radioButtonGM"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="0dp"
        android:layout_marginTop="8dp"
        android:text='"Grand Master"'
        android:textAlignment="center"
        android:textColor="#E0E0E0"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="@+id/radioButtonPro"
        app:layout_constraintRight_toRightOf="@+id/radioButtonPro"
        app:layout_constraintTop_toBottomOf="@+id/radioButtonPro"/>

</RadioGroup>

<ImageView
    android:id="@+id/kastenKnowledge"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="16dp"
    app:layout_constraintHorizontal_bias="0.517"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:srcCompat="@drawable/kasten"/>

<TextView
    android:id="@+id/testWissenstandHeader"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="Dein Wissensstand?"
    android:textAlignment="center"
    android:textColor="#511613"
    android:textSize="32sp"
    android:textStyle="bold"
    app:layout_constraintBottom_toBottomOf="@+id/kastenKnowledge"
    app:layout_constraintLeft_toLeftOf="@+id/kastenKnowledge"
    app:layout_constraintRight_toRightOf="@+id/kastenKnowledge"
    app:layout_constraintTop_toTopOf="@+id/kastenKnowledge"/>

<TextView
    android:id="@+id/testWissenstandText"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginEnd="16dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="24dp"
    android:text='Wie würdest du deinen Wissenstand\nbezüglich dem Spieleinhalt\nvon "Overwatch" beurteilen?'
    android:textAlignment="center"
    android:textColor="#E0E0E0"
    android:textSize="20sp"
    app:layout_constraintHorizontal_bias="0.512"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/testWissenstandHeader"/>

<Button
    android:id="@+id/buttonChecking"
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:layout_marginEnd="16dp"
    android:layout_marginStart="0dp"
    android:background="@drawable/button_box"
    android:text="C\nL\nI\nC\nK"
    android:textAllCaps="false"
    android:textColor="#511613"
    android:textSize="16sp"
    android:textStyle="bold"
    app:layout_constraintRight_toRightOf="parent"
    android:layout_marginRight="16dp"
    app:layout_constraintBottom_toBottomOf="@+id/radioGroup"
    android:layout_marginBottom="8dp"
    app:layout_constraintTop_toTopOf="@+id/radioGroup"
    android:layout_marginTop="8dp"
    app:layout_constraintVertical_bias="0.5"/>



<TextView
    android:id="@+id/knowledgeHint"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginLeft="0dp"
    android:layout_marginRight="0dp"
    android:text="Wenn du einen Wissenstand\nfestgelegt hast, drücke den\nKnopf daneben!"
    android:textAlignment="center"
    android:textColor="#FF4400"
    android:textSize="20sp"
    android:textStyle="bold|italic"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    android:layout_marginTop="32dp"
    app:layout_constraintTop_toBottomOf="@+id/radioGroup"/>

</android.support.constraint.ConstraintLayout>

Error message(s):

08-14 21:01:26.469 4312-4312/? I/Process: Sending signal. PID: 4312 SIG: 9
08-14 21:01:26.470 1521-1590/system_process W/AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client

                                                      --------- beginning of system
08-14 21:01:26.476 1521-1773/system_process I/WindowState: WIN DEATH: Window{ab30a43 u0 com.example.alexander.hashtagnevereverbuggy/com.example.alexander.hashtagnevereverbuggy.MainActivity}
08-14 21:01:26.480 1521-2538/system_process I/ActivityManager: Process com.example.alexander.hashtagnevereverbuggy (pid 4312) has died
08-14 21:01:26.480 1521-2538/system_process W/ActivityManager: Force removing ActivityRecord{ed88b90 u0 com.example.alexander.hashtagnevereverbuggy/.MainActivity t137}: app died, no saved state
08-14 21:01:26.491 1128-1128/? W/SurfaceFlinger: couldn't log to binary event log: overflow.
08-14 21:01:27.104 1776-1958/com.android.launcher D/EGL_emulation: eglMakeCurrent: 0x7fd4ff628200: ver 2 0
08-14 21:01:27.135 1521-1773/system_process W/InputMethodManagerService: Got RemoteException sending setActive(false) notification to pid 4312 uid 10058

@shmosel no. I'm asking why it throw a NPE even if in my try block is no error (I assume) — user8442416, Aug 14 '17 at 20:57
@shmosel I chose one radio button and pressed the button (in method `setKnowledge`) — user8442416, Aug 14 '17 at 21:04
That was not the question. The stack trace should show you which line is throwing the exception, so we don't have to guess at the problem. — shmosel, Aug 14 '17 at 21:05
@Shmosel I chose a radio button, cleared logshat and theyn pressed my button, in my question (Error message(s)) you've got what happend there — user8442416, Aug 14 '17 at 21:11

score 0 · Answer 1 · answered Aug 14 '17 at 20:57

0

Remove setContentView(R.layout.category_auswahl); inside onclick listener.

answered Aug 14 '17 at 20:57

Muthukrishnan Rajendran

11,122
3
31
41

And how to I change my layout to the next one (category_auswahl) without this method? – user8442416 Aug 14 '17 at 20:58
You should not set like that, What is there in that layout..? – Muthukrishnan Rajendran Aug 14 '17 at 21:01
Do your layouts need to be in the same activity? – Aidan Laing Aug 14 '17 at 21:08
there're 4 ImageButtons, 13 textViews, 4 ImageViews, 1 adView – user8442416 Aug 14 '17 at 21:09
@Lunkie what do you mean? – user8442416 Aug 14 '17 at 21:10
Could you just open up a new activity that has your category_auswahl layout when your button is clicked? – Aidan Laing Aug 14 '17 at 21:12
@user8442416, You can add all the item in single layout or you can use a fragment to show that..? adding setContentView multiple time is not good practice and it will lead to a lot of problems when handling view. – Muthukrishnan Rajendran Aug 14 '17 at 21:12
@MuthukrishnanRajendran I tried it but then there're way too many widgets on one layout then and it's just "ugly" to code/handle with this – user8442416 Aug 14 '17 at 21:17
In that case, you can create a fragment and show in that or you can open in another activity. – Muthukrishnan Rajendran Aug 14 '17 at 21:20

MidasLefko · Answer 2 · 2017-08-14T21:14:22.377

Change:

public knowledge checkSelection() {
    RadioButton rbNoob = (RadioButton) findViewById(R.id.radioButtonNoob);
    RadioButton rbBeginner = (RadioButton) findViewById(R.id.radioButtonBeginner);

    // etc

    else if(rbGrandMaster.isChecked()) {
        return knowledge.GM;
    }
    return null;
}

To this:

public knowledge checkSelection() {
    RadioButton rbNoob = (RadioButton) findViewById(R.id.radioButtonNoob);
    RadioButton rbBeginner = (RadioButton) findViewById(R.id.radioButtonBeginner);

    // etc

    else if(rbGrandMaster.isChecked()) {
        return knowledge.GM;
    }
    throw new NullPointerException();
}

Shahadat Hossain Shaki · Answer 3 · 2017-08-14T21:57:04.890

0

    try {
            if (checkSelection() == null) {
            throw new NullPointerException("checkSelection is null");
               }
            setContentView(R.layout.category_auswahl);
        }catch(NullPointerException n) {
            android.os.Process.killProcess(android.os.Process.myPid());
            System.exit(0);
        }

edited Aug 14 '17 at 21:57

answered Aug 14 '17 at 21:51

Shahadat Hossain Shaki

796
7
15

score 0 · Answer 4 · answered Aug 14 '17 at 22:36

Man, try-catch is not your problem in this code.

It works fine and closes your app: 08-14 21:01:26.469 4312-4312/? I/Process: Sending signal. PID: 4312 SIG: 9

You are not printing NPE, this is why you do not have it in the log.

You need to use Fragments instead of setting new content view.

You would never need System.exit(0) in Android beacuse it is against the system, you have to use finish from your Activity class.

Instead of using checking button, you can set onClickListener into your RadioGroup and you will get events every time selection has been made, so you can proceed to the next Screen (Activity or Fragment, but threre is no reason to use another one setContentView).

Here is good explanation about setContentView: Android: is using setContentView multiple times bad while changing layouts?

Why doesn't try-Catch work as it's supposed to be?

4 Answers4