无法在 Fling 上启动带有 java.lang.NullPointerException 的活动

Question

当我试图抛出这个例子时遇到了这个错误。与java空指针异常。 我的java代码

public class LearnCount extends Activity {

private FlingGallery mGallery;

public boolean onTouchEvent(MotionEvent event) {
    return mGallery.onGalleryTouchEvent(event);
}


private String[] teststr = {
        "test1","test2","test3","test4","test5"
        };


public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

    setContentView(R.layout.main);
    LinearLayout productHolder = (LinearLayout) findViewById(R.id.linearLayoutOfCount);

    mGallery = new FlingGallery(this);


        mGallery.setAdapter(new ArrayAdapter<String>(getApplicationContext(),
            android.R.layout.simple_list_item_1, teststr) {

        public View getView(int position, View convertView, ViewGroup parent) {
            System.out.println(mGallery.getCurrentPosition() + " position");
            if (convertView != null
                    && convertView instanceof GalleryViewItem) {
                GalleryViewItem galleryView = (GalleryViewItem) convertView;

                //galleryView.pImage.setImageResource(mImageIds[position]);
                galleryView.b.setText(teststr[position]);
                return galleryView;
            }

            GalleryViewItem gvi = new GalleryViewItem(getApplicationContext(), position);
            gvi.b.setText(teststr[position]);

            return gvi;
        }
    });
    productHolder.addView(mGallery);

}

public class GalleryViewItem extends TableLayout {

    private TextView b;

    public GalleryViewItem(Context context, int position) {
        super(context);

        LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View v = inflater.inflate(R.layout.test, null);
        b = (TextView) v.findViewById(R.id.test);
        this.addView(v);

    }
}

public class FlingGallery extends FrameLayout {
    // Constants

    private final int swipe_min_distance = 120;
    private final int swipe_max_off_path = 250;
    private final int swipe_threshold_veloicty = 400;

    // Properties

    private int mViewPaddingWidth = 0;
    private int mAnimationDuration = 250;
    private float mSnapBorderRatio = 0.5f;
    private boolean mIsGalleryCircular = false;

    // Members

    private int mGalleryWidth = 0;
    private boolean mIsTouched = false;
    private boolean mIsDragging = false;
    private float mCurrentOffset = 0.0f;
    private long mScrollTimestamp = 0;
    private int mFlingDirection = 0;
    public int mCurrentPosition = 0;
    private int mCurrentViewNumber = 0;

    private Context mContext;
    private Adapter mAdapter;
    private FlingGalleryView[] mViews;
    private FlingGalleryAnimation mAnimation;
    private GestureDetector mGestureDetector;
    private Interpolator mDecelerateInterpolater;

    public FlingGallery(Context context) {
        super(context);

        mContext = context;
        mAdapter = null;

        mViews = new FlingGalleryView[3];
        mViews[0] = new FlingGalleryView(0, this);
        mViews[1] = new FlingGalleryView(1, this);
        mViews[2] = new FlingGalleryView(2, this);

        mAnimation = new FlingGalleryAnimation();
        mGestureDetector = new GestureDetector(new FlingGestureDetector());
        mDecelerateInterpolater = AnimationUtils.loadInterpolator(mContext,
                android.R.anim.decelerate_interpolator);
    }

    public void setPaddingWidth(int viewPaddingWidth) {
        mViewPaddingWidth = viewPaddingWidth;
    }

    public void setAnimationDuration(int animationDuration) {
        mAnimationDuration = animationDuration;
    }

    public void setSnapBorderRatio(float snapBorderRatio) {
        mSnapBorderRatio = snapBorderRatio;
    }

    public int getCurrentPosition() {
        return mCurrentPosition;
    }

    public void setIsGalleryCircular(boolean isGalleryCircular) {
        if (mIsGalleryCircular != isGalleryCircular) {
            mIsGalleryCircular = isGalleryCircular;

            if (mCurrentPosition == getFirstPosition()) {
                // We need to reload the view immediately to the left to
                // change it to circular view or blank
                mViews[getPrevViewNumber(mCurrentViewNumber)]
                        .recycleView(getPrevPosition(mCurrentPosition));
            }

            if (mCurrentPosition == getLastPosition()) {
                // We need to reload the view immediately to the right to
                // change it to circular view or blank
                mViews[getNextViewNumber(mCurrentViewNumber)]
                        .recycleView(getNextPosition(mCurrentPosition));
            }
        }
    }

    public int getGalleryCount() {
        return (mAdapter == null) ? 0 : mAdapter.getCount();
    }

    public int getFirstPosition() {
        return 0;
    }

    public int getLastPosition() {
        return (getGalleryCount() == 0) ? 0 : getGalleryCount() - 1;
    }

    private int getPrevPosition(int relativePosition) {
        int prevPosition = relativePosition - 1;

        if (prevPosition < getFirstPosition()) {
            prevPosition = getFirstPosition() - 1;

            if (mIsGalleryCircular == true) {
                prevPosition = getLastPosition();
            }
        }

        return prevPosition;
    }

    private int getNextPosition(int relativePosition) {
        int nextPosition = relativePosition + 1;

        if (nextPosition > getLastPosition()) {
            nextPosition = getLastPosition() + 1;

            if (mIsGalleryCircular == true) {
                nextPosition = getFirstPosition();
            }
        }

        return nextPosition;
    }

    private int getPrevViewNumber(int relativeViewNumber) {
        return (relativeViewNumber == 0) ? 2 : relativeViewNumber - 1;
    }

    private int getNextViewNumber(int relativeViewNumber) {
        return (relativeViewNumber == 2) ? 0 : relativeViewNumber + 1;
    }


    protected void onLayout(boolean changed, int left, int top, int right,
            int bottom) {
        super.onLayout(changed, left, top, right, bottom);

        // Calculate our view width
        mGalleryWidth = right - left;

        if (changed == true) {
            // Position views at correct starting offsets
            mViews[0].setOffset(0, 0, mCurrentViewNumber);
            mViews[1].setOffset(0, 0, mCurrentViewNumber);
            mViews[2].setOffset(0, 0, mCurrentViewNumber);
        }
    }

    public void setAdapter(Adapter adapter) {
        mAdapter = adapter;
        mCurrentPosition = 0;
        mCurrentViewNumber = 0;

        // Load the initial views from adapter
        mViews[0].recycleView(mCurrentPosition);
        mViews[1].recycleView(getNextPosition(mCurrentPosition));
        mViews[2].recycleView(getPrevPosition(mCurrentPosition));

        // Position views at correct starting offsets
        mViews[0].setOffset(0, 0, mCurrentViewNumber);
        mViews[1].setOffset(0, 0, mCurrentViewNumber);
        mViews[2].setOffset(0, 0, mCurrentViewNumber);
    }

    private int getViewOffset(int viewNumber, int relativeViewNumber) {
        // Determine width including configured padding width
        int offsetWidth = mGalleryWidth + mViewPaddingWidth;

        // Position the previous view one measured width to left
        if (viewNumber == getPrevViewNumber(relativeViewNumber)) {
            return offsetWidth;
        }

        // Position the next view one measured width to the right
        if (viewNumber == getNextViewNumber(relativeViewNumber)) {
            return offsetWidth * -1;
        }

        return 0;
    }

    void movePrevious() {
        // Slide to previous view
        mFlingDirection = 1;
        processGesture();
    }

    void moveNext() {
        // Slide to next view
        mFlingDirection = -1;
        processGesture();
    }


    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch (keyCode) {
        case KeyEvent.KEYCODE_DPAD_LEFT:
            movePrevious();
            return true;

        case KeyEvent.KEYCODE_DPAD_RIGHT:
            moveNext();
            return true;

        case KeyEvent.KEYCODE_DPAD_CENTER:
        case KeyEvent.KEYCODE_ENTER:
        }

        return super.onKeyDown(keyCode, event);
    }

    public boolean onGalleryTouchEvent(MotionEvent event) {
        boolean consumed = mGestureDetector.onTouchEvent(event);

        if (event.getAction() == MotionEvent.ACTION_UP) {
            if (mIsTouched || mIsDragging) {
                processScrollSnap();
                processGesture();
            }
        }

        return consumed;
    }

    void processGesture() {
        int newViewNumber = mCurrentViewNumber;
        int reloadViewNumber = 0;
        int reloadPosition = 0;

        mIsTouched = false;
        mIsDragging = false;

        if (mFlingDirection > 0) {
            if (mCurrentPosition > getFirstPosition()
                    || mIsGalleryCircular == true) {
                // Determine previous view and outgoing view to recycle
                newViewNumber = getPrevViewNumber(mCurrentViewNumber);
                mCurrentPosition = getPrevPosition(mCurrentPosition);
                reloadViewNumber = getNextViewNumber(mCurrentViewNumber);
                reloadPosition = getPrevPosition(mCurrentPosition);
            }
        }

        if (mFlingDirection < 0) {
            if (mCurrentPosition < getLastPosition()
                    || mIsGalleryCircular == true) {
                // Determine the next view and outgoing view to recycle
                newViewNumber = getNextViewNumber(mCurrentViewNumber);
                mCurrentPosition = getNextPosition(mCurrentPosition);
                reloadViewNumber = getPrevViewNumber(mCurrentViewNumber);
                reloadPosition = getNextPosition(mCurrentPosition);
            }
        }

        if (newViewNumber != mCurrentViewNumber) {
            mCurrentViewNumber = newViewNumber;

            // Reload outgoing view from adapter in new position
            mViews[reloadViewNumber].recycleView(reloadPosition);
        }

        // Ensure input focus on the current view
        mViews[mCurrentViewNumber].requestFocus();

        // Run the slide animations for view transitions
        mAnimation.prepareAnimation(mCurrentViewNumber);
        this.startAnimation(mAnimation);

        // Reset fling state
        mFlingDirection = 0;
        //checkNextBackButton(mCurrentPosition);
        System.out.println("positionFiling" + mCurrentPosition);
    }

    void processScrollSnap() {
        // Snap to next view if scrolled passed snap position
        float rollEdgeWidth = mGalleryWidth * mSnapBorderRatio;
        int rollOffset = mGalleryWidth - (int) rollEdgeWidth;
        int currentOffset = mViews[mCurrentViewNumber].getCurrentOffset();

        if (currentOffset <= rollOffset * -1) {
            // Snap to previous view
            mFlingDirection = 1;
        }

        if (currentOffset >= rollOffset) {
            // Snap to next view
            mFlingDirection = -1;
        }
    }

    public class FlingGalleryView {
        private int mViewNumber;
        private FrameLayout mParentLayout;

        private FrameLayout mInvalidLayout = null;
        private LinearLayout mInternalLayout = null;
        private View mExternalView = null;

        public FlingGalleryView(int viewNumber, FrameLayout parentLayout) {
            mViewNumber = viewNumber;
            mParentLayout = parentLayout;

            // Invalid layout is used when outside gallery
            mInvalidLayout = new FrameLayout(mContext);
            mInvalidLayout.setLayoutParams(new LinearLayout.LayoutParams(
                    LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));

            // Internal layout is permanent for duration
            mInternalLayout = new LinearLayout(mContext);
            mInternalLayout.setLayoutParams(new LinearLayout.LayoutParams(
                    LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));

            mParentLayout.addView(mInternalLayout);
        }

        public void recycleView(int newPosition) {
            if (mExternalView != null) {
                mInternalLayout.removeView(mExternalView);
            }

            if (mAdapter != null) {
                if (newPosition >= getFirstPosition()
                        && newPosition <= getLastPosition()) {
                    mExternalView = mAdapter.getView(newPosition,
                            mExternalView, mInternalLayout);
                } else {
                    mExternalView = mInvalidLayout;
                }
            }

            if (mExternalView != null) {
                mInternalLayout.addView(mExternalView,
                        new LinearLayout.LayoutParams(
                                LayoutParams.FILL_PARENT,
                                LayoutParams.FILL_PARENT));
            }
        }

        public void setOffset(int xOffset, int yOffset,
                int relativeViewNumber) {
            // Scroll the target view relative to its own position relative
            // to currently displayed view
            mInternalLayout.scrollTo(getViewOffset(mViewNumber,
                    relativeViewNumber)
                    + xOffset, yOffset);
        }

        public int getCurrentOffset() {
            // Return the current scroll position
            return mInternalLayout.getScrollX();
        }

        public void requestFocus() {
            mInternalLayout.requestFocus();
        }
    }

    public class FlingGalleryAnimation extends Animation {
        private boolean mIsAnimationInProgres;
        private int mRelativeViewNumber;
        private int mInitialOffset;
        private int mTargetOffset;
        private int mTargetDistance;

        public FlingGalleryAnimation() {
            mIsAnimationInProgres = false;
            mRelativeViewNumber = 0;
            mInitialOffset = 0;
            mTargetOffset = 0;
            mTargetDistance = 0;
        }

        public void prepareAnimation(int relativeViewNumber) {
            // If we are animating relative to a new view
            if (mRelativeViewNumber != relativeViewNumber) {
                if (mIsAnimationInProgres == true) {
                    // We only have three views so if requested again to
                    // animate in same direction we must snap
                    int newDirection = (relativeViewNumber == getPrevViewNumber(mRelativeViewNumber)) ? 1
                            : -1;
                    int animDirection = (mTargetDistance < 0) ? 1 : -1;

                    // If animation in same direction
                    if (animDirection == newDirection) {
                        // Ran out of time to animate so snap to the target
                        // offset
                        mViews[0].setOffset(mTargetOffset, 0,
                                mRelativeViewNumber);
                        mViews[1].setOffset(mTargetOffset, 0,
                                mRelativeViewNumber);
                        mViews[2].setOffset(mTargetOffset, 0,
                                mRelativeViewNumber);
                    }
                }

                // Set relative view number for animation
                mRelativeViewNumber = relativeViewNumber;
            }

            // Note: In this implementation the targetOffset will always be
            // zero
            // as we are centering the view; but we include the calculations
            // of
            // targetOffset and targetDistance for use in future
            // implementations

            mInitialOffset = mViews[mRelativeViewNumber].getCurrentOffset();
            mTargetOffset = getViewOffset(mRelativeViewNumber,
                    mRelativeViewNumber);
            mTargetDistance = mTargetOffset - mInitialOffset;

            // Configure base animation properties
            this.setDuration(mAnimationDuration);
            this.setInterpolator(mDecelerateInterpolater);

            // Start/continued animation
            mIsAnimationInProgres = true;
        }


        protected void applyTransformation(float interpolatedTime,
                Transformation transformation) {
            // Ensure interpolatedTime does not over-shoot then calculate
            // new offset
            interpolatedTime = (interpolatedTime > 1.0f) ? 1.0f
                    : interpolatedTime;
            int offset = mInitialOffset
                    + (int) (mTargetDistance * interpolatedTime);

            for (int viewNumber = 0; viewNumber < 3; viewNumber++) {
                // Only need to animate the visible views as the other view
                // will always be off-screen
                if ((mTargetDistance > 0 && viewNumber != getNextViewNumber(mRelativeViewNumber))
                        || (mTargetDistance < 0 && viewNumber != getPrevViewNumber(mRelativeViewNumber))) {
                    mViews[viewNumber].setOffset(offset, 0,
                            mRelativeViewNumber);
                }
            }
        }


        public boolean getTransformation(long currentTime,
                Transformation outTransformation) {
            if (super.getTransformation(currentTime, outTransformation) == false) {
                // Perform final adjustment to offsets to cleanup animation
                mViews[0].setOffset(mTargetOffset, 0, mRelativeViewNumber);
                mViews[1].setOffset(mTargetOffset, 0, mRelativeViewNumber);
                mViews[2].setOffset(mTargetOffset, 0, mRelativeViewNumber);

                // Reached the animation target
                mIsAnimationInProgres = false;

                return false;
            }

            // Cancel if the screen touched
            if (mIsTouched || mIsDragging) {
                // Note that at this point we still consider ourselves to be
                // animating
                // because we have not yet reached the target offset; its
                // just that the
                // user has temporarily interrupted the animation with a
                // touch gesture

                return false;
            }

            return true;
        }
    }

    private class FlingGestureDetector extends GestureDetector.SimpleOnGestureListener {

        public boolean onDown(MotionEvent e) {
            // Stop animation
            mIsTouched = true;

            // Reset fling state
            mFlingDirection = 0;
            return true;
        }


        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {
            if (e2.getAction() == MotionEvent.ACTION_MOVE) {
                if (mIsDragging == false) {
                    // Stop animation
                    mIsTouched = true;

                    // Reconfigure scroll
                    mIsDragging = true;
                    mFlingDirection = 0;
                    mScrollTimestamp = System.currentTimeMillis();
                    mCurrentOffset = mViews[mCurrentViewNumber]
                            .getCurrentOffset();
                }

                float maxVelocity = mGalleryWidth
                        / (mAnimationDuration / 1000.0f);
                long timestampDelta = System.currentTimeMillis()
                        - mScrollTimestamp;
                float maxScrollDelta = maxVelocity
                        * (timestampDelta / 1000.0f);
                float currentScrollDelta = e1.getX() - e2.getX();

                if (currentScrollDelta < maxScrollDelta * -1)
                    currentScrollDelta = maxScrollDelta * -1;
                if (currentScrollDelta > maxScrollDelta)
                    currentScrollDelta = maxScrollDelta;
                int scrollOffset = Math.round(mCurrentOffset
                        + currentScrollDelta);

                // We can't scroll more than the width of our own frame
                // layout
                if (scrollOffset >= mGalleryWidth)
                    scrollOffset = mGalleryWidth;
                if (scrollOffset <= mGalleryWidth * -1)
                    scrollOffset = mGalleryWidth * -1;

                mViews[0].setOffset(scrollOffset, 0, mCurrentViewNumber);
                mViews[1].setOffset(scrollOffset, 0, mCurrentViewNumber);
                mViews[2].setOffset(scrollOffset, 0, mCurrentViewNumber);
            }

            return false;
        }


        public boolean onFling(MotionEvent e1, MotionEvent e2,
                float velocityX, float velocityY) {
            if (Math.abs(e1.getY() - e2.getY()) <= swipe_max_off_path) {
                if (e2.getX() - e1.getX() > swipe_min_distance
                        && Math.abs(velocityX) > swipe_threshold_veloicty) {
                    movePrevious();
                }

                if (e1.getX() - e2.getX() > swipe_min_distance
                        && Math.abs(velocityX) > swipe_threshold_veloicty) {
                    moveNext();
                }
            }

            return false;
        }


        public void onLongPress(MotionEvent e) {
            // Finalise scrolling
            mFlingDirection = 0;
            processGesture();
        }


        public void onShowPress(MotionEvent e) {
        }


        public boolean onSingleTapUp(MotionEvent e) {
            // Reset fling state
            mFlingDirection = 0;
            return false;
        }
    }
}

}

我的日志猫错误消息是：

我是 android 初学者，我的代码有问题吗？

Answer 1

LinearLayout productHolder = (LinearLayout) findViewById(R.id.linearLayoutOfCount);

返回 null。确保您引用了正确的 ID。