CODEWITHSUNDEEP
androidandroid-manifestforceclose
MPKenning
MPKenning

Reputation: 569

App force closing; unable to instantiate activity

I have been researching and researching this problem

It's what I've come up with so far, and I've been stuck for the past hour.

Someone please help.

The error:

10-31 18:58:23.654: E/AndroidRuntime(398): FATAL EXCEPTION: main
10-31 18:58:23.654: E/AndroidRuntime(398): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.mikenning.chemistrywizard/com.mikenning.chemistrywizard.EquationBalancer}: java.lang.NullPointerException
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1569)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.os.Looper.loop(Looper.java:123)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread.main(ActivityThread.java:3683)
10-31 18:58:23.654: E/AndroidRuntime(398):  at java.lang.reflect.Method.invokeNative(Native Method)
10-31 18:58:23.654: E/AndroidRuntime(398):  at java.lang.reflect.Method.invoke(Method.java:507)
10-31 18:58:23.654: E/AndroidRuntime(398):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-31 18:58:23.654: E/AndroidRuntime(398):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-31 18:58:23.654: E/AndroidRuntime(398):  at dalvik.system.NativeStart.main(Native Method)
10-31 18:58:23.654: E/AndroidRuntime(398): Caused by: java.lang.NullPointerException
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.Activity.findViewById(Activity.java:1647)
10-31 18:58:23.654: E/AndroidRuntime(398):  at com.mikenning.chemistrywizard.EquationBalancer.<init>(EquationBalancer.java:13)
10-31 18:58:23.654: E/AndroidRuntime(398):  at java.lang.Class.newInstanceImpl(Native Method)
10-31 18:58:23.654: E/AndroidRuntime(398):  at java.lang.Class.newInstance(Class.java:1409)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
10-31 18:58:23.654: E/AndroidRuntime(398):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1561)
10-31 18:58:23.654: E/AndroidRuntime(398):  ... 11 more

The class file:

public class EquationBalancer extends Activity {

    HorizontalScrollView reactants;

    EditText editText = new EditText(this);

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.balancelayout);

        reactants = (HorizontalScrollView) findViewById(R.id.reactants);

        EditText reactantNumberField = (EditText) findViewById(R.id.reactantsNumber);
        final int reactantNom = Integer.parseInt(reactantNumberField.getText().toString());

        Button ok = (Button) findViewById(R.id.reactantsNumberOk);
        ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                for (int i = 1; i < reactantNom; i++) {
                    editText.setHint("compound");
                    reactants.addView(editText);
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.balancelayout, menu);
        return true;
    }

}

The Android Manifest:

<manifest 
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mikenning.chemistrywizard"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="9"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme"
        android:screenOrientation="portrait" >
        <activity
            android:name="EquationBalancer"
            android:label="@string/title_activity_equation_balancer" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

The XML Layout File:

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/reactantsHowMany"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingTop="10dp"
        android:text="@string/reactantsHowMany"
        android:textSize="18dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

    <EditText
        android:id="@+id/reactantsNumber"
        android:paddingTop="5dp"
        android:layout_width="65dp"
        android:layout_height="wrap_content"
        android:layout_below="@id/reactantsHowMany"
        android:layout_marginLeft="60dp"
        android:inputType="number"
        android:hint="e.g. 4" />

    <Button 
        android:id="@+id/reactantsNumberOk"
        android:paddingTop="5dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/reactantsHowMany"
        android:layout_alignParentRight="true"
        android:layout_marginRight="60dp"
        android:layout_alignBottom="@id/reactantsNumber"
        android:text="Set" />

    <HorizontalScrollView
        android:id="@+id/reactants"
        android:paddingTop="5dp"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_below="@id/reactantsNumber" >

    </HorizontalScrollView>

</RelativeLayout>

Updated class file (updated for every suggestion):

    public class EquationBalancer extends Activity {

    HorizontalScrollView reactants;
    EditText reactantNumberField;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.balancelayout);

        reactants = (HorizontalScrollView) findViewById(R.id.reactants);

        final EditText editText = new EditText(this);
        editText.setHint("compound");

        reactantNumberField = (EditText) findViewById(R.id.reactantsNumber);


        Button ok = (Button) findViewById(R.id.reactantsNumberOk);
        ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                int reactantNom = 0;
                try{
                    reactantNom = Integer.parseInt(reactantNumberField.getText().toString());
                } catch (NullPointerException e) {
                    //ignore error
                }
                if (reactantNom != 0) {
                    for (int i = 1; i < reactantNom; i++) {
                        try{
                            reactants.addView(editText);
                        } catch (Exception e) {
                            //ignore
                        }
                    }
                } else if (reactantNom == 1) {
                    try {
                        reactants.addView(editText);
                    } catch (Exception e) {
                        //ignore
                    }
                } else {
                    Toast toast = Toast.makeText(EquationBalancer.this, "Please input the number of reactants", 
                            Toast.LENGTH_SHORT);
                    toast.show();
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.balancelayout, menu);
        return true;
    }

}

Upvotes: 1

Views: 214

Answers (2)

Marcin Orlowski
Marcin Orlowski

Reputation: 75629

Your code is invalid. This line:

Button ok = (Button) findViewById(R.id.reactantsNumberOk);

is your culprit. You initialize ok variable before your view is inflated, therefore ok is null. You have to move ok = (Button) findViewById(R.id.reactantsNumberOk); to your onCreate() after setViewContent() method, to let findViewById() actually find anything useful.

The same applies to following lines:

final EditText reactantNumberField = (EditText) findViewById(R.id.reactantsNumber);
final int reactantNom = Integer.parseInt(reactantNumberField.getText().toString());
HorizontalScrollView reactants = (HorizontalScrollView) findViewById(R.id.reactants);

these all are null and your app will still be crashing once you fix above ok initialization for the same reasons.

There's also no point of having refence to your UI elements in global scope. Valid code should look like this:

public class EquationBalancer extends Activity {

    HorizontalScrollView reactants;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.balancelayout);

        EditText reactantNumberField = (EditText) findViewById(R.id.reactantsNumber);
        int reactantNom = Integer.parseInt(reactantNumberField.getText().toString());

        reactants = (HorizontalScrollView) findViewById(R.id.reactants);

        Button ok = (Button) findViewById(R.id.reactantsNumberOk);    
        ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText editText;
                for (int i=1; i < reactantNom; i++) {
                    editText = new EditText(this);
                    editText.setHint("compound");
                    reactants.addView(editText);
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.balancelayout, menu);
        return true;
    }
}

Upvotes: 1

Simon
Simon

Reputation: 14472

You can't set references to views in your layout before you inflate the root layout with setContentView(). 

 final EditText reactantNumberField;

Then in onCreate, after setContentView()

 reactantNumberField = (EditText) findViewById(R.id.reactantsNumber);

Upvotes: 1

Related Questions