How to use isInEditMode() to see layout with custom View in the editor

I must edit a software that have a custom view, when I try to edit layout xml, Eclipse says me:

Use View.isInEditMode() in your custom views to skip code when shown in Eclipse

But I have no idea about how and where I must use isInEditMode() in the app

My xml file is

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:background="#ff000000"
    >
<TextView
     android:id="@+id/result"
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content"
     android:gravity="right"
     android:textSize="32dip"
     android:scrollbars="none"
     android:lines="1"
     android:freezesText="true"
     android:textColor="@color/result"
    />
<EditText
     android:id="@+id/input"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:gravity="left"
     android:textSize="28dip"
     android:scrollbars="none"
     android:singleLine="true"
     android:autoText="false"
     android:imeOptions="flagNoEnterAction|flagNoExtractUi"
     />
<ListView
     android:id="@+id/history"
     android:layout_width="fill_parent"
     android:layout_height="0dip"
     android:layout_weight="1"
     android:cacheColorHint="#ff000000"
     android:choiceMode="singleChoice"
     android:scrollbarStyle="outsideInset"
     android:scrollbars="none"
    />
<calculator.GraphView
     android:id="@+id/graph"
     android:layout_width="fill_parent"
     android:layout_height="0dip"
     android:layout_weight="1"
     android:visibility="gone"
     />
<include layout="@layout/keyboard" />
</LinearLayout>

And my GraphView is

public class GraphView extends View implements Grapher,
        ZoomButtonsController.OnZoomListener,
        TouchHandler.TouchHandlerInterface {
    private int width, height;
    private Matrix matrix = new Matrix();
    private Paint paint = new Paint();
    private Paint textPaint = new Paint();
    private ArrayList<Function> funcs = new ArrayList<Function>();
    private Data next = new Data(), endGraph = new Data();
    private Data graphs[] = { new Data(), new Data(), new Data(), new Data(),
            new Data() };
    private static final int GRAPHS_SIZE = 5;
    private float gwidth = 8;
    private float currentX, currentY;
    private float lastMinX;
    private Scroller scroller;
    private float boundMinY, boundMaxY;
    protected ZoomButtonsController zoomController = new ZoomButtonsController(
            this);
    private ZoomTracker zoomTracker = new ZoomTracker();
    private TouchHandler touchHandler;
    private float lastTouchX, lastTouchY;

    private static final int COL_AXIS = 0xff00a000, COL_GRID = 0xff004000,
            COL_TEXT = 0xff00ff00;

    private static final int COL_GRAPH[] = { 0xffffffff, 0xff00ffff,
            0xffffff00, 0xffff00ff, 0xff80ff80 };

    public GraphView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public GraphView(Context context) {
        super(context);
        touchHandler = new TouchHandler(this);
        init(context);
    }

    private void init(Context context) {
        zoomController.setOnZoomListener(this);
        scroller = new Scroller(context);
        paint.setAntiAlias(false);
        textPaint.setAntiAlias(true);
    }

    @SuppressLint("WrongCall")
    public String captureScreenshot() {
        Bitmap bitmap = Bitmap.createBitmap(width, height,
                Bitmap.Config.RGB_565);
        Canvas canvas = new Canvas(bitmap);
        onDraw(canvas);
        return Util.saveBitmap(bitmap, Grapher.SCREENSHOT_DIR, "calculator");
    }

    private void clearAllGraph() {
        for (int i = 0; i < GRAPHS_SIZE; ++i) {
            graphs[i].clear();
        }
    }

    public void setFunctions(ArrayList<Function> fs) {
        funcs.clear();
        for (Function f : fs) {
            int arity = f.arity();
            if (arity == 0 || arity == 1) {
                funcs.add(f);
            }
        }
        clearAllGraph();
        invalidate();
    }

    public void setFunction(Function f) {
        funcs.clear();
        if (f != null) {
            funcs.add(f);
        }
        clearAllGraph();
        invalidate();
    }

    public void onVisibilityChanged(boolean visible) {
    }

    public void onZoom(boolean zoomIn) {
        if (zoomIn) {
            if (canZoomIn()) {
                gwidth /= 2;
                invalidateGraphs();
            }
        } else {
            if (canZoomOut()) {
                gwidth *= 2;
                invalidateGraphs();
            }
        }
        zoomController.setZoomInEnabled(canZoomIn());
        zoomController.setZoomOutEnabled(canZoomOut());
    }

    public void onResume() {
    }

    public void onPause() {
    }

    public void onDetachedFromWindow() {
        zoomController.setVisible(false);
        super.onDetachedFromWindow();
    }

    protected void onSizeChanged(int w, int h, int ow, int oh) {
        width = w;
        height = h;
        clearAllGraph();
    }

    protected void onDraw(Canvas canvas) {
        if (funcs.size() == 0) {
            return;
        }
        if (scroller.computeScrollOffset()) {
            final float scale = gwidth / width;
            currentX = scroller.getCurrX() * scale;
            currentY = scroller.getCurrY() * scale;
            if (!scroller.isFinished()) {
                invalidate();
            }
        }
        drawGraph(canvas);
    }

    private float eval(Function f, float x) {
        float v = (float) f.eval(x);

        if (v < -10000f) {
            return -10000f;
        }
        if (v > 10000f) {
            return 10000f;
        }
        return v;
    }

    private float distance2(float x1, float y1, float x2, float y2, float y) {
        final float dx = x2 - x1;
        final float dy = y2 - y1;
        final float up = dx * (y1 + y2 - y - y);
        return up * up / (dx * dx + dy * dy);
    }

    private void computeGraph(Function f, float minX, float maxX, float minY,
            float maxY, Data graph) {
        if (f.arity() == 0) {
            float v = (float) f.eval();
            if (v < -10000f) {
                v = -10000f;
            }
            if (v > 10000f) {
                v = 10000f;
            }
            graph.clear();
            graph.push(minX, v);
            graph.push(maxX, v);
            return;
        }

        final float scale = width / gwidth;
        final float maxStep = 15.8976f / scale;
        final float minStep = .05f / scale;
        float ythresh = 1 / scale;
        ythresh = ythresh * ythresh;
        if (!graph.empty()) {
            if (minX >= lastMinX) {
                graph.eraseBefore(minX);
            } else {
                graph.eraseAfter(maxX);
                maxX = Math.min(maxX, graph.firstX());
                graph.swap(endGraph);
            }
        }
        if (graph.empty()) {
            graph.push(minX, eval(f, minX));
        }
        float leftX, leftY;
        float rightX = graph.topX(), rightY = graph.topY();
        int nEval = 1;
        while (true) {
            leftX = rightX;
            leftY = rightY;
            if (leftX > maxX) {
                break;
            }
            if (next.empty()) {
                float x = leftX + maxStep;
                next.push(x, eval(f, x));
                ++nEval;
            }
            rightX = next.topX();
            rightY = next.topY();
            next.pop();

            if (leftY != leftY && rightY != rightY) { // NaN
                continue;
            }

            float dx = rightX - leftX;
            float middleX = (leftX + rightX) / 2;
            float middleY = eval(f, middleX);
            ++nEval;
            boolean middleIsOutside = (middleY < leftY && middleY < rightY)
                    || (leftY < middleY && rightY < middleY);
            if (dx < minStep) {
                if (middleIsOutside) {
                    graph.push(rightX, Float.NaN);
                }
                graph.push(rightX, rightY);
                continue;
            }
            if (middleIsOutside
                    && ((leftY < minY && rightY > maxY) || (leftY > maxY && rightY < minY))) {
                graph.push(rightX, Float.NaN);
                graph.push(rightX, rightY);
                continue;
            }

            if (!middleIsOutside) {

                if (distance2(leftX, leftY, rightX, rightY, middleY) < ythresh) {
                    graph.push(rightX, rightY);
                    continue;
                }
            }
            next.push(rightX, rightY);
            next.push(middleX, middleY);
            rightX = leftX;
            rightY = leftY;
        }
        if (!endGraph.empty()) {
            graph.append(endGraph);
        }
        long t2 = System.currentTimeMillis();

        next.clear();
        endGraph.clear();
    }

    private static Path path = new Path();

    private Path graphToPath(Data graph) {
        boolean first = true;
        int size = graph.size;
        float[] xs = graph.xs;
        float[] ys = graph.ys;
        path.rewind();
        for (int i = 0; i < size; ++i) {
            float y = ys[i];
            float x = xs[i];
            // Calculator.log("path " + x + ' ' + y);
            if (y == y) { // !NaN
                if (first) {
                    path.moveTo(x, y);
                    first = false;
                } else {
                    path.lineTo(x, y);
                }
            } else {
                first = true;
            }
        }
        return path;
    }

    private static final float NTICKS = 15;

    private static float stepFactor(float w) {
        float f = 1;
        while (w / f > NTICKS) {
            f *= 10;
        }
        while (w / f < NTICKS / 10) {
            f /= 10;
        }
        float r = w / f;
        if (r < NTICKS / 5) {
            return f / 5;
        } else if (r < NTICKS / 2) {
            return f / 2;
        } else {
            return f;
        }
    }

    private static StringBuilder b = new StringBuilder();
    private static char[] buf = new char[20];

    private static StringBuilder format(float fv) {
        int pos = 0;
        boolean addDot = false;
        int v = Math.round(fv * 100);
        boolean isNeg = v < 0;
        v = isNeg ? -v : v;
        for (int i = 0; i < 2; ++i) {
            int digit = v % 10;
            v /= 10;
            if (digit != 0 || addDot) {
                buf[pos++] = (char) ('0' + digit);
                addDot = true;
            }
        }
        if (addDot) {
            buf[pos++] = '.';
        }
        if (v == 0) {
            buf[pos++] = '0';
        }
        while (v != 0) {
            buf[pos++] = (char) ('0' + (v % 10));
            v /= 10;
        }
        if (isNeg) {
            buf[pos++] = '-';
        }
        b.setLength(0);
        b.append(buf, 0, pos);
        b.reverse();
        return b;
    }

    private void drawGraph(Canvas canvas) {
        long t1 = System.currentTimeMillis();
        float minX = currentX - gwidth / 2;
        float maxX = minX + gwidth;
        float ywidth = gwidth * height / width;
        float minY = currentY - ywidth / 2;
        float maxY = minY + ywidth;
        if (minY < boundMinY || maxY > boundMaxY) {
            float halfw = ywidth / 2;
            boundMinY = minY - halfw;
            boundMaxY = maxY + halfw;
            clearAllGraph();
        }

        canvas.drawColor(0xff000000);

        paint.setStrokeWidth(0);
        paint.setAntiAlias(false);
        paint.setStyle(Paint.Style.STROKE);

        final float h2 = height / 2f;
        final float scale = width / gwidth;

        float x0 = -minX * scale;
        boolean drawYAxis = true;
        if (x0 < 25) {
            x0 = 25;
            // drawYAxis = false;
        } else if (x0 > width - 3) {
            x0 = width - 3;
            // drawYAxis = false;
        }
        float y0 = maxY * scale;
        if (y0 < 3) {
            y0 = 3;
        } else if (y0 > height - 15) {
            y0 = height - 15;
        }

        final float tickSize = 3;
        final float y2 = y0 + tickSize;
        paint.setColor(COL_GRID);
        float step = stepFactor(gwidth);
        float v = ((int) (minX / step)) * step;
        textPaint.setColor(COL_TEXT);
        textPaint.setTextSize(12);
        textPaint.setTextAlign(Paint.Align.CENTER);
        float stepScale = step * scale;
        for (float x = (v - minX) * scale; x <= width; x += stepScale, v += step) {
            canvas.drawLine(x, 0, x, height, paint);
            if (!(-.001f < v && v < .001f)) {
                StringBuilder b = format(v);
                canvas.drawText(b, 0, b.length(), x, y2 + 10, textPaint);
            }
        }

        final float x1 = x0 - tickSize;
        v = ((int) (minY / step)) * step;
        textPaint.setTextAlign(Paint.Align.RIGHT);
        for (float y = height - (v - minY) * scale; y >= 0; y -= stepScale, v += step) {
            canvas.drawLine(0, y, width, y, paint);
            if (!(-.001f < v && v < .001f)) {
                StringBuilder b = format(v);
                canvas.drawText(b, 0, b.length(), x1, y + 4, textPaint);
            }
        }

        paint.setColor(COL_AXIS);
        if (drawYAxis) {
            canvas.drawLine(x0, 0, x0, height, paint);
        }
        canvas.drawLine(0, y0, width, y0, paint);

        matrix.reset();
        matrix.preTranslate(-currentX, -currentY);
        matrix.postScale(scale, -scale);
        matrix.postTranslate(width / 2, height / 2);

        paint.setStrokeWidth(0);
        paint.setAntiAlias(false);

        int n = Math.min(funcs.size(), GRAPHS_SIZE);
        for (int i = 0; i < n; ++i) {
            computeGraph(funcs.get(i), minX, maxX, boundMinY, boundMaxY,
                    graphs[i]);
            Path path = graphToPath(graphs[i]);
            path.transform(matrix);
            paint.setColor(COL_GRAPH[i]);
            canvas.drawPath(path, paint);
        }
        lastMinX = minX;
    }

    private boolean canZoomIn() {
        return gwidth > 1f;
    }

    private boolean canZoomOut() {
        return gwidth < 50;
    }

    private void invalidateGraphs() {
        clearAllGraph();
        boundMinY = boundMaxY = 0;
        invalidate();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return touchHandler != null ? touchHandler.onTouchEvent(event) : super
                .onTouchEvent(event);
    }

    public void onTouchDown(float x, float y) {
        zoomController.setVisible(true);
        if (!scroller.isFinished()) {
            scroller.abortAnimation();
        }
        lastTouchX = x;
        lastTouchY = y;
    }

    public void onTouchMove(float x, float y) {
        float deltaX = x - lastTouchX;
        float deltaY = y - lastTouchY;
        if (deltaX < -1 || deltaX > 1 || deltaY < -1 || deltaY > 1) {
            scroll(-deltaX, deltaY);
            lastTouchX = x;
            lastTouchY = y;
            invalidate();
        }
    }

    public void onTouchUp(float x, float y) {
        final float scale = width / gwidth;
        float sx = -touchHandler.velocityTracker.getXVelocity();
        float sy = touchHandler.velocityTracker.getYVelocity();
        final float asx = Math.abs(sx);
        final float asy = Math.abs(sy);
        if (asx < asy / 3) {
            sx = 0;
        } else if (asy < asx / 3) {
            sy = 0;
        }
        scroller.fling(Math.round(currentX * scale),
                Math.round(currentY * scale), Math.round(sx), Math.round(sy),
                -10000, 10000, -10000, 10000);
        invalidate();
    }

    public void onTouchZoomDown(float x1, float y1, float x2, float y2) {
        zoomTracker.start(gwidth, x1, y1, x2, y2);
    }

    public void onTouchZoomMove(float x1, float y1, float x2, float y2) {
        if (!zoomTracker.update(x1, y1, x2, y2)) {
            return;
        }
        float targetGwidth = zoomTracker.value;
        if (targetGwidth > .25f && targetGwidth < 200) {
            gwidth = targetGwidth;
        }
        invalidateGraphs();
    }

    private void scroll(float deltaX, float deltaY) {
        final float scale = gwidth / width;
        float dx = deltaX * scale;
        float dy = deltaY * scale;
        final float adx = Math.abs(dx);
        final float ady = Math.abs(dy);
        if (adx < ady / 3) {
            dx = 0;
        } else if (ady < adx / 3) {
            dy = 0;
        }
        currentX += dx;
        currentY += dy;
    }
}

The error Log of the XML editor

java.lang.NullPointerException
    at android.widget.ZoomButtonsController.createContainer(ZoomButtonsController.java:266)
    at android.widget.ZoomButtonsController.<init>(ZoomButtonsController.java:212)
    at calculator.GraphView.<init>(GraphView.java:43)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(    at sun.reflect.NativeConstructorAccessorImpl.newInstance(    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(    at java.lang.reflect.Constructor.newInstance(    at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.instantiateClass(ProjectCallback.java:422)
    at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.loadView(ProjectCallback.java:179)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:207)
    at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:135)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:746)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:64)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:718)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:372)

isInEditMode()should be used inside the Custom View constructor. Try the following code:

     public class GraphView extends View implements Grapher
        {

         public GraphView(Context context, AttributeSet attrs) {
                super(context, attrs);
                if(!isInEditMode())
                 init(context);
            }

            public GraphView(Context context) {
                super(context);
               if(!isInEditMode()){
                touchHandler = new TouchHandler(this);
                init(context);
              }
            }

public class CustomTextView extends TextView {

public CustomTextView(Context context) {
    super(context);
}

public CustomTextView(Context context, AttributeSet attrs) {
    super(context, attrs);

    if (!isInEditMode()) {
        createTypeface(context, attrs); //whatever added functionality you are trying to add to Widget, call that inside this condition. 
    }

}

public CustomTextView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}


//Typeface I wan to set to my Custom TextView It can be any other functionality of your choice

private void createTypeface(Context context, AttributeSet attrs) {

    TypedArray styledAttrs = context.obtainStyledAttributes(attrs,
            R.styleable.CustomTextView);
    String fontName = styledAttrs
            .getString(R.styleable.CustomTextView_Typeface);
    styledAttrs.recycle();

    if (fontName != null) {
        Typeface typeface = Typeface.createFromAsset(context.getAssets(),
                "fonts/" + fontName);

        setTypeface(typeface);
        styledAttrs.recycle();
    }
}

}