Android GridView添加头部问题的解决

我们都知道ListView有addHeaderView和addFooterView两个方法。其中addHeaderView是添加头部布局，addFooterView是添加底部布局。但是GridView却没有这两个方法这个时候就需要重写GridView了。geogle官方给出了重写的HeaderGridView不知道为什么没有添加到官方api里面。代码如下:

public class HeaderGridView extends GridView {
  private static final String TAG = "HeaderGridView";
  /**
   * A class that represents a fixed view in a list, for example a header at the top
   * or a footer at the bottom.
   */
  private static class FixedViewInfo {
    /** The view to add to the grid */
    public View view;
    public ViewGroup viewContainer;
    /** The data backing the view. This is returned from {@link ListAdapter#getItem(int)}. */
    public Object data;
    /** <code>true</code> if the fixed view should be selectable in the grid */
    public boolean isSelectable;
  }
  private ArrayList<FixedViewInfo> mHeaderViewInfos = new ArrayList<FixedViewInfo>();
  private void initHeaderGridView() {
    super.setClipChildren(false);
  }
  public HeaderGridView(Context context) {
    super(context);
    initHeaderGridView();
  }
  public HeaderGridView(Context context, AttributeSet attrs) {
    super(context, attrs);
    initHeaderGridView();
  }
  public HeaderGridView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    initHeaderGridView();
  }
  @SuppressLint("NewApi")
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    ListAdapter adapter = getAdapter();
    if (adapter != null && adapter instanceof HeaderViewGridAdapter) {
      ((HeaderViewGridAdapter) adapter).setNumColumns(getNumColumns());
    }
  }
  @Override
  public void setClipChildren(boolean clipChildren) {
    // Ignore, since the header rows depend on not being clipped
  }
  /**
   * Add a fixed view to appear at the top of the grid. If addHeaderView is
   * called more than once, the views will appear in the order they were
   * added. Views added using this call can take focus if they want.
   * <p>
   * NOTE: Call this before calling setAdapter. This is so HeaderGridView can wrap
   * the supplied cursor with one that will also account for header views.
   *
   * @param v The view to add.
   * @param data Data to associate with this view
   * @param isSelectable whether the item is selectable
   */
  public void addHeaderView(View v, Object data, boolean isSelectable) {
    ListAdapter adapter = getAdapter();
    if (adapter != null && ! (adapter instanceof HeaderViewGridAdapter)) {
      throw new IllegalStateException(
          "Cannot add header view to grid -- setAdapter has already been called.");
    }
    FixedViewInfo info = new FixedViewInfo();
    FrameLayout fl = new FullWidthFixedViewLayout(getContext());
    fl.addView(v);
    info.view = v;
    info.viewContainer = fl;
    info.data = data;
    info.isSelectable = isSelectable;
    mHeaderViewInfos.add(info);
    // in the case of re-adding a header view, or adding one later on,
    // we need to notify the observer
    if (adapter != null) {
      ((HeaderViewGridAdapter) adapter).notifyDataSetChanged();
    }
  }
  /**
   * Add a fixed view to appear at the top of the grid. If addHeaderView is
   * called more than once, the views will appear in the order they were
   * added. Views added using this call can take focus if they want.
   * <p>
   * NOTE: Call this before calling setAdapter. This is so HeaderGridView can wrap
   * the supplied cursor with one that will also account for header views.
   *
   * @param v The view to add.
   */
  public void addHeaderView(View v) {
    addHeaderView(v, null, true);
  }
  public int getHeaderViewCount() {
    return mHeaderViewInfos.size();
  }
  /**
   * Removes a previously-added header view.
   *
   * @param v The view to remove
   * @return true if the view was removed, false if the view was not a header
   *     view
   */
  public boolean removeHeaderView(View v) {
    if (mHeaderViewInfos.size() > 0) {
      boolean result = false;
      ListAdapter adapter = getAdapter();
      if (adapter != null && ((HeaderViewGridAdapter) adapter).removeHeader(v)) {
        result = true;
      }
      removeFixedViewInfo(v, mHeaderViewInfos);
      return result;
    }
    return false;
  }
  private void removeFixedViewInfo(View v, ArrayList<FixedViewInfo> where) {
    int len = where.size();
    for (int i = 0; i < len; ++i) {
      FixedViewInfo info = where.get(i);
      if (info.view == v) {
        where.remove(i);
        break;
      }
    }
  }
  @SuppressLint("NewApi")
  @Override
  public void setAdapter(ListAdapter adapter) {
    if (mHeaderViewInfos.size() > 0) {
      HeaderViewGridAdapter hadapter = new HeaderViewGridAdapter(mHeaderViewInfos, adapter);
      int numColumns = getNumColumns();
      if (numColumns > 1) {
        hadapter.setNumColumns(numColumns);
      }
      super.setAdapter(hadapter);
    } else {
      super.setAdapter(adapter);
    }
  }
  private class FullWidthFixedViewLayout extends FrameLayout {
    public FullWidthFixedViewLayout(Context context) {
      super(context);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
      int targetWidth = HeaderGridView.this.getMeasuredWidth()
          - HeaderGridView.this.getPaddingLeft()
          - HeaderGridView.this.getPaddingRight();
      widthMeasureSpec = MeasureSpec.makeMeasureSpec(targetWidth,
          MeasureSpec.getMode(widthMeasureSpec));
      super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
  }
  /**
   * ListAdapter used when a HeaderGridView has header views. This ListAdapter
   * wraps another one and also keeps track of the header views and their
   * associated data objects.
   *<p>This is intended as a base class; you will probably not need to
   * use this class directly in your own code.
   */
  private static class HeaderViewGridAdapter implements WrapperListAdapter, Filterable {
    // This is used to notify the container of updates relating to number of columns
    // or headers changing, which changes the number of placeholders needed
    private final DataSetObservable mDataSetObservable = new DataSetObservable();
    private final ListAdapter mAdapter;
    private int mNumColumns = 1;
    // This ArrayList is assumed to NOT be null.
    ArrayList<FixedViewInfo> mHeaderViewInfos;
    boolean mAreAllFixedViewsSelectable;
    private final boolean mIsFilterable;
    public HeaderViewGridAdapter(ArrayList<FixedViewInfo> headerViewInfos, ListAdapter adapter) {
      mAdapter = adapter;
      mIsFilterable = adapter instanceof Filterable;
      if (headerViewInfos == null) {
        throw new IllegalArgumentException("headerViewInfos cannot be null");
      }
      mHeaderViewInfos = headerViewInfos;
      mAreAllFixedViewsSelectable = areAllListInfosSelectable(mHeaderViewInfos);
    }
    public int getHeadersCount() {
      return mHeaderViewInfos.size();
    }
    @Override
    public boolean isEmpty() {
      return (mAdapter == null || mAdapter.isEmpty()) && getHeadersCount() == 0;
    }
    public void setNumColumns(int numColumns) {
      if (numColumns < 1) {
        throw new IllegalArgumentException("Number of columns must be 1 or more");
      }
      if (mNumColumns != numColumns) {
        mNumColumns = numColumns;
        notifyDataSetChanged();
      }
    }
    private boolean areAllListInfosSelectable(ArrayList<FixedViewInfo> infos) {
      if (infos != null) {
        for (FixedViewInfo info : infos) {
          if (!info.isSelectable) {
            return false;
          }
        }
      }
      return true;
    }
    public boolean removeHeader(View v) {
      for (int i = 0; i < mHeaderViewInfos.size(); i++) {
        FixedViewInfo info = mHeaderViewInfos.get(i);
        if (info.view == v) {
          mHeaderViewInfos.remove(i);
          mAreAllFixedViewsSelectable = areAllListInfosSelectable(mHeaderViewInfos);
          mDataSetObservable.notifyChanged();
          return true;
        }
      }
      return false;
    }
    @Override
    public int getCount() {
      if (mAdapter != null) {
        return getHeadersCount() * mNumColumns + mAdapter.getCount();
      } else {
        return getHeadersCount() * mNumColumns;
      }
    }
    @Override
    public boolean areAllItemsEnabled() {
      if (mAdapter != null) {
        return mAreAllFixedViewsSelectable && mAdapter.areAllItemsEnabled();
      } else {
        return true;
      }
    }
    @Override
    public boolean isEnabled(int position) {
      // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
      int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
      if (position < numHeadersAndPlaceholders) {
        return (position % mNumColumns == 0)
            && mHeaderViewInfos.get(position / mNumColumns).isSelectable;
      }
      // Adapter
      final int adjPosition = position - numHeadersAndPlaceholders;
      int adapterCount = 0;
      if (mAdapter != null) {
        adapterCount = mAdapter.getCount();
        if (adjPosition < adapterCount) {
          return mAdapter.isEnabled(adjPosition);
        }
      }
      throw new ArrayIndexOutOfBoundsException(position);
    }
    @Override
    public Object getItem(int position) {
      // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
      int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
      if (position < numHeadersAndPlaceholders) {
        if (position % mNumColumns == 0) {
          return mHeaderViewInfos.get(position / mNumColumns).data;
        }
        return null;
      }
      // Adapter
      final int adjPosition = position - numHeadersAndPlaceholders;
      int adapterCount = 0;
      if (mAdapter != null) {
        adapterCount = mAdapter.getCount();
        if (adjPosition < adapterCount) {
          return mAdapter.getItem(adjPosition);
        }
      }
      throw new ArrayIndexOutOfBoundsException(position);
    }
    @Override
    public long getItemId(int position) {
      int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
      if (mAdapter != null && position >= numHeadersAndPlaceholders) {
        int adjPosition = position - numHeadersAndPlaceholders;
        int adapterCount = mAdapter.getCount();
        if (adjPosition < adapterCount) {
          return mAdapter.getItemId(adjPosition);
        }
      }
      return -1;
    }
    @Override
    public boolean hasStableIds() {
      if (mAdapter != null) {
        return mAdapter.hasStableIds();
      }
      return false;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
      int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns ;
      if (position < numHeadersAndPlaceholders) {
        View headerViewContainer = mHeaderViewInfos
            .get(position / mNumColumns).viewContainer;
        if (position % mNumColumns == 0) {
          return headerViewContainer;
        } else {
          if (convertView == null) {
            convertView = new View(parent.getContext());
          }
          // We need to do this because GridView uses the height of the last item
          // in a row to determine the height for the entire row.
          convertView.setVisibility(View.INVISIBLE);
          convertView.setMinimumHeight(headerViewContainer.getHeight());
          return convertView;
        }
      }
      // Adapter
      final int adjPosition = position - numHeadersAndPlaceholders;
      int adapterCount = 0;
      if (mAdapter != null) {
        adapterCount = mAdapter.getCount();
        if (adjPosition < adapterCount) {
          return mAdapter.getView(adjPosition, convertView, parent);
        }
      }
      throw new ArrayIndexOutOfBoundsException(position);
    }
    @Override
    public int getItemViewType(int position) {
      int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
      if (position < numHeadersAndPlaceholders && (position % mNumColumns != 0)) {
        // Placeholders get the last view type number
        return mAdapter != null ? mAdapter.getViewTypeCount() : 1;
      }
      if (mAdapter != null && position >= numHeadersAndPlaceholders) {
        int adjPosition = position - numHeadersAndPlaceholders;
        int adapterCount = mAdapter.getCount();
        if (adjPosition < adapterCount) {
          return mAdapter.getItemViewType(adjPosition);
        }
      }
      return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
    }
    @Override
    public int getViewTypeCount() {
      if (mAdapter != null) {
        return mAdapter.getViewTypeCount() + 1;
      }
      return 2;
    }
    @Override
    public void registerDataSetObserver(DataSetObserver observer) {
      mDataSetObservable.registerObserver(observer);
      if (mAdapter != null) {
        mAdapter.registerDataSetObserver(observer);
      }
    }
    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {
      mDataSetObservable.unregisterObserver(observer);
      if (mAdapter != null) {
        mAdapter.unregisterDataSetObserver(observer);
      }
    }
    @Override
    public Filter getFilter() {
      if (mIsFilterable) {
        return ((Filterable) mAdapter).getFilter();
      }
      return null;
    }
    @Override
    public ListAdapter getWrappedAdapter() {
      return mAdapter;
    }
    public void notifyDataSetChanged() {
      mDataSetObservable.notifyChanged();
    }
  }
}

用法和ListView的addHeaderView一样。

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