java - 添加和删​​除水平列表项 onScroll

Question

我需要显示水平 ListView 项目的无限滚动(意味着需要重复项目)例如

a,b,c,d,e,f,a,b,c,d,e,f,a,b,....

粗体是屏幕上可见的项目

过程是在到达最后一个列表项后重复列表项，我尝试在滚动列表时添加列表项，所以我自定义了水平 ListView 类。但是在右侧添加列表项后向左滚动时，我得到了 ArrayIndexOutOfBoundsException。我试图在基本适配器中添加 Integer.MAX VALUE 选项以获得无限数量的项目，但它在定位项目时没有帮助(设置选择())。如果有人知道如何添加和删除水平列表项的方法，请分享。

Answer 1

不是扩展 BaseAdapter 而是扩展 ArrayAdapter。

解决方案 1::

注意::在 AgarwalActivity.java 中为水平 ListView 设置 boolean 变量 isHorizo​​ntalListView = true。

Horizo​​ntalListView.java

public class HorizontalListView extends AdapterView<ListAdapter> {

    public boolean mAlwaysOverrideTouch = true;
    protected ListAdapter mAdapter;
    private int mLeftViewIndex = -1;
    private int mRightViewIndex = 0;
    protected int mCurrentX;
    protected int mNextX;
    private int mMaxX = Integer.MAX_VALUE;
    private int mDisplayOffset = 0;
    protected Scroller mScroller;
    private GestureDetector mGesture;
    private Queue<View> mRemovedViewQueue = new LinkedList<View>();
    private OnItemSelectedListener mOnItemSelected;
    private OnItemClickListener mOnItemClicked;
    private OnItemLongClickListener mOnItemLongClicked;
    private boolean mDataChanged = false;


    public HorizontalListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    private synchronized void initView() {
        mLeftViewIndex = -1;
        mRightViewIndex = 0;
        mDisplayOffset = 0;
        mCurrentX = 0;
        mNextX = 0;
        mMaxX = Integer.MAX_VALUE;
        mScroller = new Scroller(getContext());
        mGesture = new GestureDetector(getContext(), mOnGesture);
    }

    @Override
    public void setOnItemSelectedListener(AdapterView.OnItemSelectedListener listener) {
        mOnItemSelected = listener;
    }

    @Override
    public void setOnItemClickListener(AdapterView.OnItemClickListener listener){
        mOnItemClicked = listener;
    }

    @Override
    public void setOnItemLongClickListener(AdapterView.OnItemLongClickListener listener) {
        mOnItemLongClicked = listener;
    }

    private DataSetObserver mDataObserver = new DataSetObserver() {

        @Override
        public void onChanged() {
            synchronized(HorizontalListView.this){
                mDataChanged = true;
            }
            invalidate();
            requestLayout();
        }

        @Override
        public void onInvalidated() {
            reset();
            invalidate();
            requestLayout();
        }

    };

    @Override
    public ListAdapter getAdapter() {
        return mAdapter;
    }

    @Override
    public View getSelectedView() {
        //TODO: implement
        return null;
    }

    @Override
    public void setAdapter(ListAdapter adapter) {
        if(mAdapter != null) {
            mAdapter.unregisterDataSetObserver(mDataObserver);
        }
        mAdapter = adapter;
        mAdapter.registerDataSetObserver(mDataObserver);
        reset();
    }

    private synchronized void reset(){
        initView();
        removeAllViewsInLayout();
        requestLayout();
    }

    @Override
    public void setSelection(int position) {
        //TODO: implement
    }

    private void addAndMeasureChild(final View child, int viewPos) {
        LayoutParams params = child.getLayoutParams();
        if(params == null) {
            params = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
        }

        addViewInLayout(child, viewPos, params, true);
        child.measure(MeasureSpec.makeMeasureSpec(getWidth(), MeasureSpec.AT_MOST),
                MeasureSpec.makeMeasureSpec(getHeight(), MeasureSpec.AT_MOST));
    }

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

        if(mAdapter == null){
            return;
        }

        if(mDataChanged){
            int oldCurrentX = mCurrentX;
            initView();
            removeAllViewsInLayout();
            mNextX = oldCurrentX;
            mDataChanged = false;
        }

        if(mScroller.computeScrollOffset()){
            int scrollx = mScroller.getCurrX();
            mNextX = scrollx;
        }

        if(mNextX <= 0){
            mNextX = 0;
            mScroller.forceFinished(true);
        }
        if(mNextX >= mMaxX) {
            mNextX = mMaxX;
            mScroller.forceFinished(true);
        }

        int dx = mCurrentX - mNextX;

        removeNonVisibleItems(dx);
        fillList(dx);
        positionItems(dx);

        mCurrentX = mNextX;

        if(!mScroller.isFinished()){
            post(new Runnable() {

                public void run() {
                    // TODO Auto-generated method stub
                    requestLayout();
                }
            });

        }
    }

    private void fillList(final int dx) {
        int edge = 0;
        View child = getChildAt(getChildCount()-1);
        if(child != null) {
            edge = child.getRight();
        }
        fillListRight(edge, dx);

        edge = 0;
        child = getChildAt(0);
        if(child != null) {
            edge = child.getLeft();
        }
        fillListLeft(edge, dx);


    }

    private void fillListRight(int rightEdge, final int dx) {
        while(rightEdge + dx < getWidth() && mRightViewIndex < mAdapter.getCount()) {

            View child = mAdapter.getView(mRightViewIndex, mRemovedViewQueue.poll(), this);
            addAndMeasureChild(child, -1);
            rightEdge += child.getMeasuredWidth();

            if(mRightViewIndex == mAdapter.getCount()-1) {
                mMaxX = mCurrentX + rightEdge - getWidth();
            }

            if (mMaxX < 0) {
                mMaxX = 0;
            }
            mRightViewIndex++;
        }

    }

    private void fillListLeft(int leftEdge, final int dx) {
        while(leftEdge + dx > 0 && mLeftViewIndex >= 0) {
            View child = mAdapter.getView(mLeftViewIndex, mRemovedViewQueue.poll(), this);
            addAndMeasureChild(child, 0);
            leftEdge -= child.getMeasuredWidth();
            mLeftViewIndex--;
            mDisplayOffset -= child.getMeasuredWidth();
        }
    }

    private void removeNonVisibleItems(final int dx) {
        View child = getChildAt(0);
        while(child != null && child.getRight() + dx <= 0) {
            mDisplayOffset += child.getMeasuredWidth();
            mRemovedViewQueue.offer(child);
            removeViewInLayout(child);
            mLeftViewIndex++;
            child = getChildAt(0);

        }

        child = getChildAt(getChildCount()-1);
        while(child != null && child.getLeft() + dx >= getWidth()) {
            mRemovedViewQueue.offer(child);
            removeViewInLayout(child);
            mRightViewIndex--;
            child = getChildAt(getChildCount()-1);
        }
    }

    private void positionItems(final int dx) {
        if(getChildCount() > 0){
            mDisplayOffset += dx;
            int left = mDisplayOffset;
            for(int i=0;i<getChildCount();i++){
                View child = getChildAt(i);
                int childWidth = child.getMeasuredWidth();
                child.layout(left, 0, left + childWidth, child.getMeasuredHeight());
                left += childWidth;
            }
        }
    }

    public synchronized void scrollTo(int x) {
        mScroller.startScroll(mNextX, 0, x - mNextX, 0);
        requestLayout();
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean handled = super.dispatchTouchEvent(ev);
        handled |= mGesture.onTouchEvent(ev);
        return handled;
    }

    protected boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
                float velocityY) {
        synchronized(HorizontalListView.this){
            mScroller.fling(mNextX, 0, (int)-velocityX, 0, 0, mMaxX, 0, 0);
        }
        requestLayout();

        return true;
    }

    protected boolean onDown(MotionEvent e) {
        mScroller.forceFinished(true);
        return true;
    }

    private OnGestureListener mOnGesture = new GestureDetector.SimpleOnGestureListener() {

        @Override
        public boolean onDown(MotionEvent e) {
            return HorizontalListView.this.onDown(e);
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
                float velocityY) {
            return HorizontalListView.this.onFling(e1, e2, velocityX, velocityY);
        }

        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {

            synchronized(HorizontalListView.this){
                mNextX += (int)distanceX;
            }
            requestLayout();

            return true;
        }

        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {
            for(int i=0;i<getChildCount();i++){
                View child = getChildAt(i);
                if (isEventWithinView(e, child)) {
                    if(mOnItemClicked != null){
                        mOnItemClicked.onItemClick(HorizontalListView.this, child, mLeftViewIndex + 1 + i, mAdapter.getItemId( mLeftViewIndex + 1 + i ));
                    }
                    if(mOnItemSelected != null){
                        mOnItemSelected.onItemSelected(HorizontalListView.this, child, mLeftViewIndex + 1 + i, mAdapter.getItemId( mLeftViewIndex + 1 + i ));
                    }
                    break;
                }

            }
            return true;
        }

        @Override
        public void onLongPress(MotionEvent e) {
            int childCount = getChildCount();
            for (int i = 0; i < childCount; i++) {
                View child = getChildAt(i);
                if (isEventWithinView(e, child)) {
                    if (mOnItemLongClicked != null) {
                        mOnItemLongClicked.onItemLongClick(HorizontalListView.this, child, mLeftViewIndex + 1 + i, mAdapter.getItemId(mLeftViewIndex + 1 + i));
                    }
                    break;
                }

            }
        }

        private boolean isEventWithinView(MotionEvent e, View child) {
            Rect viewRect = new Rect();
            int[] childPosition = new int[2];
            child.getLocationOnScreen(childPosition);
            int left = childPosition[0];
            int right = left + child.getWidth();
            int top = childPosition[1];
            int bottom = top + child.getHeight();
            viewRect.set(left, top, right, bottom);
            return viewRect.contains((int) e.getRawX(), (int) e.getRawY());
        }
    };



}

AgarwalActivity.java

public class AgarwalActivity extends Activity{

    private LayoutInflater _inflater;
    private ListView listView;
    private HorizontalListView hListView;
    private RankingsAdapter rankingsAdapter;
    private boolean isHorizontalListView = false;


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);  
            if(isHorizontalListView){
                setContentView(R.layout.listviewdemo);
                hListView = (HorizontalListView) findViewById(R.id.listview);  
            }else{
                setContentView(R.layout.listview);
                listView=(ListView)findViewById(R.id.listView);
            }

        ArrayList<String> rankingArrayList = new ArrayList<String>();
        for(int i=0;i<25;i++)
           rankingArrayList.add("agarwal"+i);

        _inflater= LayoutInflater.from(AgarwalActivity.this);    

        rankingsAdapter = new RankingsAdapter(AgarwalActivity.this,R.id.text,rankingArrayList);
            if(isHorizontalListView)
                hListView.setAdapter(rankingsAdapter);
            else
            listView.setAdapter(rankingsAdapter);

    }


    private class RankingsAdapter extends ArrayAdapter<String>{
        private ArrayList<String> _row_list;

        public static final int HALF_MAX_VALUE = Integer.MAX_VALUE/2;
        public final int MIDDLE;
        public RankingsAdapter(Context context,int textViewResourceId,ArrayList<String> arrL) {
            // TODO Auto-generated constructor stub
            super(context,textViewResourceId, arrL);
            _row_list = arrL;
            MIDDLE = HALF_MAX_VALUE - HALF_MAX_VALUE % _row_list.size();
        }
        public int getCount() {
            // TODO Auto-generated method stub
            return Integer.MAX_VALUE;
        }
        public String getItem(int position) {
            // TODO Auto-generated method stub
            return _row_list.get(position % _row_list.size());
        }
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position % _row_list.size();
        }

        public View getView(final int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            ViewHolder holder = null;

            if(convertView == null){
                holder = new ViewHolder();
                convertView = (LinearLayout)_inflater.inflate(R.layout.text_layout, null);
                //getting the IDs
                holder.driver = (TextView)convertView.findViewById(R.id.text);
                convertView.setTag(holder);
            } else {

                holder=(ViewHolder)convertView.getTag();
            }
            //Settng bean values to row components
            holder.driver.setText(_row_list.get(position % _row_list.size()));

            return convertView;
        }//getView()

        class ViewHolder{
            //holding the components
            TextView driver;
        }//ViewHolder--Class inside CountriesAdapter

    }//RankingsAdapter-inner class

}//AgarwalActivity-class

listview.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >


    <ListView
        android:id="@+id/listView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

    </ListView>

</RelativeLayout>

listviewdemo.xml

<?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="#fff"
  >

  <com.vl.agarwal.HorizontalListView
    android:id="@+id/listview"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="#ddd"
  />

</LinearLayout>

text_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >


<TextView
    android:id="@+id/text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:gravity="center_vertical"
    android:minHeight="?android:attr/listPreferredItemHeight"
    android:paddingLeft="6dip"
    android:textAppearance="?android:attr/textAppearanceLarge" />

</LinearLayout>

-------------------------------------------- --------------------------------------

解决方案 2:: 使用图库作为水平 ListView

行.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical" >

  <TextView
      android:id="@+id/itemtext"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_margin="20dp"
      android:textColor="@android:color/white"
      android:textStyle="bold"
      android:textSize="30sp"/>

</LinearLayout>

ma​​in.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical" >

  <TextView
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:text="@string/hello" />
  <Gallery
      android:id="@+id/horizontallistview"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content" />

</LinearLayout>

AgarwalActivity.java

public class AgarwalActivity extends Activity {

 Gallery myHorizontalListView;

private RankingsAdapter rankingsAdapter;

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
  ArrayList<String> rankingArrayList = new ArrayList<String>();
  for(int i=0;i<25;i++)
     rankingArrayList.add("agarwal"+i);

  DisplayMetrics metrics = new DisplayMetrics();
  this.getWindowManager().getDefaultDisplay().getMetrics(metrics);

  myHorizontalListView = (Gallery)findViewById(R.id.horizontallistview);
  MarginLayoutParams mlp = (MarginLayoutParams) myHorizontalListView.getLayoutParams();
  mlp.setMargins(-(metrics.widthPixels/2), 
                 mlp.topMargin, 
                 mlp.rightMargin, 
                 mlp.bottomMargin
  );


  rankingsAdapter = new RankingsAdapter(AgarwalActivity.this,R.id.itemtext,rankingArrayList);
  myHorizontalListView.setAdapter(rankingsAdapter);

  myHorizontalListView.setSelection(10,true);

      myHorizontalListView.setOnItemClickListener(new OnItemClickListener(){

   @Override
   public void onItemClick(AdapterView<?> parent, View view, int position,
     long id) {
    Toast.makeText(
      AgarwalActivity.this,
      parent.getItemAtPosition(position).toString() + " Clicked",
      Toast.LENGTH_LONG)
      .show();

   }});

  }




    private class RankingsAdapter extends ArrayAdapter<String>{
        private ArrayList<String> _row_list;

        public static final int HALF_MAX_VALUE = Integer.MAX_VALUE/2;
        public final int MIDDLE;
        public RankingsAdapter(Context context,int textViewResourceId,ArrayList<String> arrL) {
            // TODO Auto-generated constructor stub
            super(context,textViewResourceId, arrL);
            _row_list = arrL;
            MIDDLE = HALF_MAX_VALUE - HALF_MAX_VALUE % _row_list.size();
        }
        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return Integer.MAX_VALUE;
        }
        @Override
        public String getItem(int position) {
            // TODO Auto-generated method stub
            return _row_list.get(position % _row_list.size());
        }
        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position % _row_list.size();
        }

        @Override
        public View getView(final int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            View rowView = LayoutInflater
                     .from(parent.getContext())
                     .inflate(R.layout.row, null);
                   TextView listTextView = (TextView)rowView.findViewById(R.id.itemtext);
                   listTextView.setText(_row_list.get(position % _row_list.size()));

                   return rowView;
        }//getView()
    }//RankingsAdapter-inner class
}//AgarwalActivity-class