Can't open activities caused by: java.lang.NullPointerException : <p>I am developing app for kids drawing alphabet according to alphabet stroke. I cannot run DrawingActivity cause by java.lang.NullPointerException.I not really strong in coding. I feel that null error come from <code>getIntent().getExtras().getString("type");</code>.So,i change the code to <code>getIntent().getStringExtra("type");</code>,but still can't run DrawingActivity. Please help me guys. Really appreciate it.</p>

<p>This is my error logcat:</p>

<pre><code>12-05 23:47:29.498 9620-9620/com.example.user.mygame E/AndroidRuntime: FATAL EXCEPTION: main
                                                                       Process: com.example.user.mygame, PID: 9620
                                                                       java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.user.mygame/com.example.user.mygame.DrawingActivity}: java.lang.NullPointerException
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2247)
                                                                           at android.app.ActivityThread.access$800(ActivityThread.java:141)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:136)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5111)
                                                                           at java.lang.reflect.Method.invokeNative(Native Method)
                                                                           at java.lang.reflect.Method.invoke(Method.java:515)
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:806)
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622)
                                                                           at dalvik.system.NativeStart.main(Native Method)
                                                                        Caused by: java.lang.NullPointerException
                                                                           at com.example.user.mygame.DrawingActivity.onCreate(DrawingActivity.java:156)
                                                                           at android.app.Activity.performCreate(Activity.java:5248)
                                                                           at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
                                                                           at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162)
                                                                           at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2247) 
                                                                           at android.app.ActivityThread.access$800(ActivityThread.java:141) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                           at android.os.Looper.loop(Looper.java:136) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5111) 
                                                                           at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                           at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:806) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:622) 
                                                                           at dalvik.system.NativeStart.main(Native Method) 
</code></pre>

<p>This is my DrawingActivity.java:</p>

<pre><code>package com.example.user.mygame;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Cap;
import android.graphics.Paint.Join;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.Path.Direction;
import android.graphics.Rect;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout.LayoutParams;
import com.google.android.gms.location.DetectedActivity;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;

public class DrawingActivity extends Activity implements OnClickListener, OnTouchListener {

    View drawingView;
    DrawingView dv;
    LayoutParams params;
    ViewGroup parent;
    ImageView nextBtn;
    ImageView playBtn;
    ImageView prevBtn;
    private Paint mPaint;
    private Integer position;
    private int totalItem;
    private String type;

    public class DrawingView extends View {
        private static final float TOUCH_TOLERANCE = 4.0f;
        private Bitmap bm;
        private Paint circlePaint;
        private Path circlePath;
        Context context;
        private Bitmap mBitmap;
        private Paint mBitmapPaint;
        private Canvas mCanvas;
        private Path mPath;
        private float mX;
        private float mY;

        public DrawingView(Context c) {
            super(c);
            this.context = c;
            this.mPath = new Path();
            this.mBitmapPaint = new Paint(4);
            this.circlePaint = new Paint();
            this.circlePath = new Path();
            this.circlePaint.setAntiAlias(true);
            this.circlePaint.setColor(Color.BLACK);
            this.circlePaint.setStyle(Style.STROKE);
            this.circlePaint.setStrokeJoin(Join.MITER);
            this.circlePaint.setStrokeWidth(TOUCH_TOLERANCE);
        }

        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
            this.mBitmap = Bitmap.createBitmap(w, h, Config.ARGB_8888);
            this.mCanvas = new Canvas(this.mBitmap);
            if (DrawingActivity.this.type.equals(Resource.DRAWING_ALPHABET)) {
                this.bm = BitmapFactory.decodeResource(getResources(), Resource.capitalStoke[DrawingActivity.this.position]);
            }
            this.mCanvas.drawBitmap(this.bm, new Rect(0, 0, this.bm.getWidth(), this.bm.getHeight()), new Rect(0, 0, this.mCanvas.getWidth(), this.mCanvas.getHeight()), this.mBitmapPaint);
        }

        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            canvas.drawBitmap(this.mBitmap, 0.0f, 0.0f, this.mBitmapPaint);
            canvas.drawPath(this.mPath, DrawingActivity.this.mPaint);
            canvas.drawPath(this.circlePath, this.circlePaint);
        }

        private void touch_start(float x, float y) {
            this.mPath.reset();
            this.mPath.moveTo(x, y);
            this.mX = x;
            this.mY = y;
        }

        private void touch_move(float x, float y) {
            float dx = Math.abs(x - this.mX);
            float dy = Math.abs(y - this.mY);
            if (dx &gt;= TOUCH_TOLERANCE || dy &gt;= TOUCH_TOLERANCE) {
                this.mPath.quadTo(this.mX, this.mY, (this.mX + x) / 2.0f, (this.mY + y) / 2.0f);
                this.mX = x;
                this.mY = y;
                this.circlePath.reset();
                this.circlePath.addCircle(this.mX, this.mY, BitmapDescriptorFactory.HUE_ORANGE, Direction.CW);
            }
        }

        private void touch_up() {
            this.mPath.lineTo(this.mX, this.mY);
            this.circlePath.reset();
            this.mCanvas.drawPath(this.mPath, DrawingActivity.this.mPaint);
            this.mPath.reset();
        }

        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();
            switch (event.getAction()) {
                case DetectedActivity.IN_VEHICLE /*0*/:
                    touch_start(x, y);
                    invalidate();
                    break;
                case DetectedActivity.ON_BICYCLE /*1*/:
                    touch_up();
                    invalidate();
                    break;
                case DetectedActivity.ON_FOOT /*2*/:
                    touch_move(x, y);
                    invalidate();
                    break;
            }
            return true;
        }

        public void resetCanvas() {
            this.bm = null;
            this.mBitmap = null;
            System.gc();
        }
    }

    public DrawingActivity() {
        this.type = "";
        this.position = 0;
        this.totalItem = 0;

        this.nextBtn = null;
        this.playBtn = null;
        this.prevBtn = null;
        this.drawingView = null;
        this.parent = null;
        this.params = null;
    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(1);
        setContentView(R.layout.drawing_alphabet);
        this.type = getIntent().getExtras().getString("type");
        this.nextBtn = (ImageView) findViewById(R.id.nextId);
        this.playBtn = (ImageView) findViewById(R.id.playId);
        this.prevBtn = (ImageView) findViewById(R.id.prevId);
        this.nextBtn.setOnClickListener(this);
        this.nextBtn.setOnTouchListener(this);
        this.prevBtn.setOnClickListener(this);
        this.prevBtn.setOnTouchListener(this);
        this.playBtn.setOnClickListener(this);
        this.playBtn.setOnTouchListener(this);
        this.drawingView = findViewById(R.id.drawingViewId);
        this.params = (LayoutParams) this.drawingView.getLayoutParams();
        this.dv = new DrawingView(this);
        this.dv.setLayoutParams(this.params);
        this.parent = (ViewGroup) this.drawingView.getParent();
        int index = this.parent.indexOfChild(this.drawingView);
        this.parent.removeView(this.drawingView);
        this.parent.addView(this.dv, index);
        if (this.type.equals(Resource.DRAWING_ALPHABET)) {
            this.totalItem = Resource.capitalStoke.length;
        }
        this.mPaint = new Paint();
        this.mPaint.setAntiAlias(true);
        this.mPaint.setDither(true);
        this.mPaint.setColor(Color.BLACK);
        this.mPaint.setStyle(Style.STROKE);
        this.mPaint.setStrokeJoin(Join.ROUND);
        this.mPaint.setStrokeCap(Cap.ROUND);
        this.mPaint.setStrokeWidth(16.0f);
        updatePreviousButton();
    }


    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case DetectedActivity.IN_VEHICLE /*0*/:
                if (v.getId() == R.id.nextId || v.getId() == R.id.playId || v.getId() == R.id.prevId) {
                    v.setAlpha(0.5f);
                    break;
                }
            case DetectedActivity.ON_BICYCLE /*1*/:
                if (v.getId() == R.id.nextId || v.getId() == R.id.playId || v.getId() == R.id.prevId) {
                    v.setAlpha(1.0f);
                    break;
                }
        }
        return false;
    }

    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.nextId:
                this.position = this.position + 1;
                changeStroke();
            case R.id.playId:
                changeStroke();
            case R.id.prevId:
                this.position = this.position - 1;
                changeStroke();
            default:
        }
    }

    private void changeStroke() {
        updateNextButton();
        updatePreviousButton();
        int index = this.parent.indexOfChild(this.dv);
        this.dv.resetCanvas();
        this.dv = null;
        this.parent.removeViewAt(index);
        this.dv = new DrawingView(this);
        this.dv.setLayoutParams(this.params);
        this.parent.addView(this.dv, index);
    }

    private void updateNextButton() {
        if (this.position == this.totalItem - 1) {
            this.nextBtn.setAlpha(0.5f);
            this.nextBtn.setClickable(false);
            return;
        }
        this.nextBtn.setAlpha(1.0f);
        this.nextBtn.setClickable(true);
    }

    private void updatePreviousButton() {
        if (this.position == 0) {
            this.prevBtn.setAlpha(0.5f);
            this.prevBtn.setClickable(false);
            return;
        }
        this.prevBtn.setAlpha(1.0f);
        this.prevBtn.setClickable(true);
    }
}
</code></pre>

<p>This is my drawing_alphabet.xml:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg_drawing"&gt;
    &lt;View
        android:id="@+id/drawingViewId"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="0dp"
        android:layout_marginRight="64dp"
        android:layout_marginEnd="64dp"/&gt;
        &lt;ImageView
            android:id="@+id/prevId"
            android:layout_width="52dp"
            android:layout_height="52dp"
            android:src="@drawable/back_icon"
            android:layout_gravity="top"
            android:layout_marginTop="49dp"
            android:layout_alignParentTop="true"
            android:layout_alignLeft="@+id/nextId"
            android:layout_alignStart="@+id/nextId" /&gt;
        &lt;ImageView
            android:id="@+id/nextId"
            android:layout_width="52dp"
            android:layout_height="52dp"
            android:src="@drawable/next_icon"
            android:layout_gravity="bottom"
            android:layout_marginTop="61dp"
            android:layout_below="@+id/prevId"
            android:layout_alignParentRight="true"
            android:layout_alignParentEnd="true" /&gt; /

&lt;/RelativeLayout&gt;
</code></pre>

<p>This is my manifest.xml:</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.user.mygame"&gt;

    &lt;application
        android:allowBackup="false"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        android:name="android.support.multidex.MultiDexApplication"&gt;
        &lt;activity android:name=".MainActivity"
            android:screenOrientation="landscape"&gt;
            &lt;intent-filter&gt;
                &lt;action android:name="android.intent.action.MAIN" /&gt;
                &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
            &lt;/intent-filter&gt;
        &lt;/activity&gt;
        &lt;activity android:label="@string/app_name" android:name="com.example.user.mygame.AlphabetActivity" android:screenOrientation="landscape" /&gt;
        &lt;activity android:label="@string/app_name" android:name="com.example.user.mygame.DrawingActivity" android:screenOrientation="landscape" /&gt;
    &lt;/application&gt;

&lt;/manifest&gt;
</code></pre>

<p>This is my resource.java:</p>

<pre><code>package com.example.user.mygame;


public class Resource {

    public static String DRAWING_ALPHABET;
    public static Integer[] capitalStoke;
    Integer[] alphabetCapital;
    Integer[] alphabetSound;
    Integer[] alphabetImage;

    static {
        DRAWING_ALPHABET = "alphabet";
        setCapitalStoke(new Integer[]{Integer.valueOf(R.drawable.capital_letters_stroke_01),
                Integer.valueOf(R.drawable.capital_letters_stroke_02),
                Integer.valueOf(R.drawable.capital_letters_stroke_03),
                Integer.valueOf(R.drawable.capital_letters_stroke_04),
                Integer.valueOf(R.drawable.capital_letters_stroke_05),
                Integer.valueOf(R.drawable.capital_letters_stroke_06),
                Integer.valueOf(R.drawable.capital_letters_stroke_07),
                Integer.valueOf(R.drawable.capital_letters_stroke_08),
                Integer.valueOf(R.drawable.capital_letters_stroke_09),
                Integer.valueOf(R.drawable.capital_letters_stroke_10),
                Integer.valueOf(R.drawable.capital_letters_stroke_11),
                Integer.valueOf(R.drawable.capital_letters_stroke_12),
                Integer.valueOf(R.drawable.capital_letters_stroke_13),
                Integer.valueOf(R.drawable.capital_letters_stroke_14),
                Integer.valueOf(R.drawable.capital_letters_stroke_15),
                Integer.valueOf(R.drawable.capital_letters_stroke_16),
                Integer.valueOf(R.drawable.capital_letters_stroke_17),
                Integer.valueOf(R.drawable.capital_letters_stroke_18),
                Integer.valueOf(R.drawable.capital_letters_stroke_19),
                Integer.valueOf(R.drawable.capital_letters_stroke_20),
                Integer.valueOf(R.drawable.capital_letters_stroke_21),
                Integer.valueOf(R.drawable.capital_letters_stroke_22),
                Integer.valueOf(R.drawable.capital_letters_stroke_23),
                Integer.valueOf(R.drawable.capital_letters_stroke_24),
                Integer.valueOf(R.drawable.capital_letters_stroke_25),
                Integer.valueOf(R.drawable.capital_letters_stroke_26)});

    }

    public static Integer[] getCapitalStoke() {
        return capitalStoke;
    }
    public static void setCapitalStoke(Integer[] capitalStoke) {
        Resource.capitalStoke = capitalStoke;
    }

    public Resource() {
        this.alphabetCapital = new Integer[]{
                Integer.valueOf(R.drawable.img_letter_001),
                Integer.valueOf(R.drawable.img_letter_002),
                Integer.valueOf(R.drawable.img_letter_003),
                Integer.valueOf(R.drawable.img_letter_004),
                Integer.valueOf(R.drawable.img_letter_005),
                Integer.valueOf(R.drawable.img_letter_006),
                Integer.valueOf(R.drawable.img_letter_007),
                Integer.valueOf(R.drawable.img_letter_008),
                Integer.valueOf(R.drawable.img_letter_009),
                Integer.valueOf(R.drawable.img_letter_010),
                Integer.valueOf(R.drawable.img_letter_011),
                Integer.valueOf(R.drawable.img_letter_012),
                Integer.valueOf(R.drawable.img_letter_013),
                Integer.valueOf(R.drawable.img_letter_014),
                Integer.valueOf(R.drawable.img_letter_015),
                Integer.valueOf(R.drawable.img_letter_016),
                Integer.valueOf(R.drawable.img_letter_017),
                Integer.valueOf(R.drawable.img_letter_018),
                Integer.valueOf(R.drawable.img_letter_019),
                Integer.valueOf(R.drawable.img_letter_020),
                Integer.valueOf(R.drawable.img_letter_021),
                Integer.valueOf(R.drawable.img_letter_022),
                Integer.valueOf(R.drawable.img_letter_023),
                Integer.valueOf(R.drawable.img_letter_024),
                Integer.valueOf(R.drawable.img_letter_025),
                Integer.valueOf(R.drawable.img_letter_026)};

        this.alphabetSound = new Integer[]{
                Integer.valueOf(R.raw.snd_a),
                Integer.valueOf(R.raw.snd_b),
                Integer.valueOf(R.raw.snd_c),};

        this.alphabetImage = new Integer[]{
                Integer.valueOf(R.drawable.image_1),
                Integer.valueOf(R.drawable.image_2),
                Integer.valueOf(R.drawable.image_3)};
    }

}
</code></pre>
