最近使用GridView,希望能像ListView一样可以添加footerView，来实现滚动到底部自动加载更多的功能。但是GridView没提供添加FooterView的方法，只能自己实现了。参考了HeaderGridView的实现，本以为添加FooterView会很简单，但发现还是有很多不同的地方。
给GridView的添加Footer的原理就是，假如说我们的GridView每行显示3列，也就是说每一行有3个ItemView,但我们的FooterVIew要占整个一行怎么办，那我们就把FooterView所在的一行给它补上两个view，然后把这两个View的高度设置成FooterView的高度，不然的话，如果高度小了，FooterView会显示不全,并且把这两个补全的View的Visibile设置成INVISIBLE，这样FooterView就能完全的显示在一整行了。如图：
现在我们要做的有两件事情，一个是获取FooterView的高度，因为我们要给两个补全的view设置和FooterView统一的高度，另一件事就是我们要把FooterView 的宽度设置成GridView整行的宽度。代码如下：
public void addFooterView(View v, Object data, boolean isSelectable) {
ListAdapter adapter = getAdapter();
if (adapter != null && !(adapter instanceof FooterViewGridAdapter)) {
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;
mFooterViewInfos.add(info);
if (adapter != null) {
((FooterViewGridAdapter) adapter).notifyDataSetChanged();
}
}这是我们添加FooterView的方法，其中有个FullWidthFixedViewLayout的ViewGroup,这是一个内部类，重写了它的onMeasure方法，把它的宽度设置成GridView的宽度，该类实现如下：
private class FullWidthFixedViewLayout extends FrameLayout {
public FullWidthFixedViewLayout(Context context) {
super(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int targetWidth = FooterGridView.this.getMeasuredWidth() - FooterGridView.this.getPaddingLeft() - FooterGridView.this.getPaddingRight();
widthMeasureSpec = MeasureSpec.makeMeasureSpec(targetWidth, MeasureSpec.getMode(widthMeasureSpec));
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
}上面这种情况是iitemView正好占满一行的情况，如果itemView没有占满一行怎么办，那么我们也要把空缺的列给补上，并且隐藏掉。同样也需要把它的高度设置成itemView的高度。如图：
获取itemView的高度方法如下：
private int getRowHeight() {
int childHeight = 0;
ListAdapter lAdapter = getAdapter();
if (lAdapter != null) {
int mItemCount = lAdapter instanceof FooterViewGridAdapter ? ((FooterViewGridAdapter) lAdapter).getWrappedAdapter().getCount() : lAdapter
.getCount();
final int count = mItemCount;
if (count > 0) {
View child = getAdapter().getView(count - 1, null, this);
AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams();
if (p == null) {
p = (AbsListView.LayoutParams) generateDefaultLayoutParams();
child.setLayoutParams(p);
}
int childHeightSpec = getChildMeasureSpec(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 0, p.height);
child.measure(0, childHeightSpec);
childHeight = child.getMeasuredHeight();
}
}
return childHeight;
}这里的FooterViewGridAdapter是我们自定义的内部Adapter,它实现了WrapperListAdapter，如果设置了FooterView,我们就用它来包装外面传过来的Adapter.完整代码如下：
import android.content.Context;
import android.database.DataSetObservable;
import android.database.DataSetObserver;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.FrameLayout;
import android.widget.GridView;
import android.widget.ListAdapter;
import android.widget.WrapperListAdapter;
public class FooterGridView extends GridView {
private static final String TAG = "FooterGridView";
/**
* 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> mFooterViewInfos = new ArrayList<FixedViewInfo>();
private void initFooterGridView() {
super.setClipChildren(false);
}
public FooterGridView(Context context) {
super(context);
initFooterGridView();
}
public FooterGridView(Context context, AttributeSet attrs) {
super(context, attrs);
initFooterGridView();
}
public FooterGridView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initFooterGridView();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
ListAdapter adapter = getAdapter();
if (adapter != null && adapter instanceof FooterViewGridAdapter) {
FooterViewGridAdapter fAdapter = (FooterViewGridAdapter) adapter;
fAdapter.setNumColumns(getNumColumns());
fAdapter.setColumnWidth(getColumnWidth());
fAdapter.setRowHeight(getRowHeight());
}
}
@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 addFooterView 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 FooterGridView 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 addFooterView(View v, Object data, boolean isSelectable) {
ListAdapter adapter = getAdapter();
if (adapter != null && !(adapter instanceof FooterViewGridAdapter)) {
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;
mFooterViewInfos.add(info);
if (adapter != null) {
((FooterViewGridAdapter) adapter).notifyDataSetChanged();
}
}
/**
* Add a fixed view to appear at the top of the grid. If addFooterView 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 FooterGridView can
* wrap the supplied cursor with one that will also account for header
* views.
*
* @param v
* The view to add.
*/
public void addFooterView(View v) {
addFooterView(v, null, true);
}
public int getFooterViewCount() {
return mFooterViewInfos.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 removeFooterView(View v) {
if (mFooterViewInfos.size() > 0) {
boolean result = false;
ListAdapter adapter = getAdapter();
if (adapter != null && ((FooterViewGridAdapter) adapter).removeFooter(v)) {
result = true;
}
removeFixedViewInfo(v, mFooterViewInfos);
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;
}
}
}
/**
* 设置Adapter的方法，如果设置了footerView,就用FooterViewGridAdapter来封装。
*/
@Override
public void setAdapter(ListAdapter adapter) {
if (mFooterViewInfos.size() > 0) {
FooterViewGridAdapter hadapter = new FooterViewGridAdapter(mFooterViewInfos, adapter);
int numColumns = getNumColumns();
if (numColumns > 1) {
hadapter.setNumColumns(numColumns);
}
super.setAdapter(hadapter);
} else {
super.setAdapter(adapter);
}
}
// 获取每行高度的方法
private int getRowHeight() {
int childHeight = 0;
ListAdapter lAdapter = getAdapter();
if (lAdapter != null) {
int mItemCount = lAdapter instanceof FooterViewGridAdapter && ((FooterViewGridAdapter) lAdapter).getWrappedAdapter() != null ? ((FooterViewGridAdapter) lAdapter).getWrappedAdapter().getCount() : 0;
final int count = mItemCount;
if (count > 0) {
View child = getAdapter().getView(count - 1, null, this);
AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams();
if (p == null) {
p = (AbsListView.LayoutParams) generateDefaultLayoutParams();
child.setLayoutParams(p);
}
int childHeightSpec = getChildMeasureSpec(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED), 0, p.height);
child.measure(0, childHeightSpec);
childHeight = child.getMeasuredHeight();
}
}
return childHeight;
}
private class FullWidthFixedViewLayout extends FrameLayout {
public FullWidthFixedViewLayout(Context context) {
super(context);
}
// 重写onMeasure 使footerView的宽度占整行GridView的宽度
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int targetWidth = FooterGridView.this.getMeasuredWidth() - FooterGridView.this.getPaddingLeft() - FooterGridView.this.getPaddingRight();
widthMeasureSpec = MeasureSpec.makeMeasureSpec(targetWidth, MeasureSpec.getMode(widthMeasureSpec));
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
}
/**
* ListAdapter used when a FooterGridView 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 FooterViewGridAdapter 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;
private int mRowHeight;
private int mColumnWidth;
// This ArrayList is assumed to NOT be null.
ArrayList<FixedViewInfo> mFooterViewInfos;
boolean mAreAllFixedViewsSelectable;
private final boolean mIsFilterable;
public FooterViewGridAdapter(ArrayList<FixedViewInfo> headerViewInfos, ListAdapter adapter) {
mAdapter = adapter;
mIsFilterable = adapter instanceof Filterable;
if (headerViewInfos == null) {
throw new IllegalArgumentException("headerViewInfos cannot be null");
}
mFooterViewInfos = headerViewInfos;
mAreAllFixedViewsSelectable = areAllListInfosSelectable(mFooterViewInfos);
}
public int getFootersCount() {
return mFooterViewInfos.size();
}
@Override
public boolean isEmpty() {
return (mAdapter == null || mAdapter.isEmpty()) && getFootersCount() == 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();
}
}
public void setColumnWidth(int columnWidth) {
this.mColumnWidth = columnWidth;
}
public void setRowHeight(int rowHeight) {
this.mRowHeight = rowHeight;
}
private boolean areAllListInfosSelectable(ArrayList<FixedViewInfo> infos) {
if (infos != null) {
for (FixedViewInfo info : infos) {
if (!info.isSelectable) {
return false;
}
}
}
return true;
}
public boolean removeFooter(View v) {
for (int i = 0; i < mFooterViewInfos.size(); i++) {
FixedViewInfo info = mFooterViewInfos.get(i);
if (info.view == v) {
mFooterViewInfos.remove(i);
mAreAllFixedViewsSelectable = areAllListInfosSelectable(mFooterViewInfos);
mDataSetObservable.notifyChanged();
return true;
}
}
return false;
}
/**
* 如果设置了footerView而adapter为空的话，则count的数量等于footerView的个数 乘以 GridView每行的列数
* 如果adapter不为空的话，则count的数量等于footerView的个数 乘以 GridView每行的列数 加上
* adapter的count 加上补全View的个数
*/
@Override
public int getCount() {
if (mAdapter != null) {
if (mAdapter.getCount() % mNumColumns == 0) {
return getFootersCount() * mNumColumns + mAdapter.getCount();
} else {
return getFootersCount() * mNumColumns + mAdapter.getCount() + (mNumColumns - mAdapter.getCount() % mNumColumns);
}
} else {
return getFootersCount() * mNumColumns;
}
}
@Override
public boolean areAllItemsEnabled() {
if (mAdapter != null) {
return mAreAllFixedViewsSelectable && mAdapter.areAllItemsEnabled();
} else {
return true;
}
}
@Override
public boolean isEnabled(int position) {
if (mAdapter != null) {
int adapterCount = mAdapter.getCount();
if (position < adapterCount) {
return mAdapter.isEnabled(position);
} else {
if (adapterCount % mNumColumns == 0) {
return mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns).isSelectable;
} else {
return mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns - 1).isSelectable;
}
}
}
return position % mNumColumns == 0 && mFooterViewInfos.get(position / mNumColumns).isSelectable;
}
@Override
public Object getItem(int position) {
if (mAdapter != null) {
int adapterCount = mAdapter.getCount();
if (position < adapterCount) {
return mAdapter.getItem(position);
} else {
if (adapterCount % mNumColumns == 0) {
return mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns).data;
} else {
return mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns - 1).data;
}
}
}
return position % mNumColumns == 0 ? mFooterViewInfos.get(position / mNumColumns).data : null;
}
@Override
public long getItemId(int position) {
if (mAdapter != null) {
return mAdapter.getItemId(position);
}
return -1;
}
@Override
public boolean hasStableIds() {
if (mAdapter != null) {
return mAdapter.hasStableIds();
}
return false;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (mAdapter != null) {
int adapterCount = mAdapter.getCount();
if (position < adapterCount) {// 如果position小于adapterCount则只返回itemView
return mAdapter.getView(position, convertView, parent);
} else if (adapterCount % mNumColumns == 0) {// 如果adapterCount余每行显示的列数等于0的话，则说明itemView正好占满一行，就不需要补全View
View footerViewContainer = mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns).viewContainer;
if (position % mNumColumns == 0) {// 最后一行的第一个应该是footerView
return footerViewContainer;
} else {// 最后一行为FooterView 补全的View
if (convertView == null) {
convertView = new View(parent.getContext());
}
convertView.setVisibility(View.INVISIBLE);
convertView.setMinimumHeight(footerViewContainer.getHeight());
return convertView;
}
} else {// 这是itemView没有占满一行的情况，则需要补全
int vacantCount = mNumColumns - adapterCount % mNumColumns;// 补全View的个数
if (position < (adapterCount + vacantCount)) {
if (convertView == null) {
convertView = new View(parent.getContext());
}
convertView.setVisibility(View.INVISIBLE);
convertView.setMinimumWidth(mColumnWidth);
convertView.setMinimumHeight(mRowHeight);
return convertView;
} else {
View footerViewContainer = mFooterViewInfos.get(position / mNumColumns - adapterCount / mNumColumns - 1).viewContainer;
if (position % mNumColumns == 0) {
return footerViewContainer;
} else {
if (convertView == null) {
convertView = new View(parent.getContext());
}
convertView.setVisibility(View.INVISIBLE);
convertView.setMinimumHeight(footerViewContainer.getHeight());
return convertView;
}
}
}
} else {// 如果外部adapter为空的话，则只返回FooterView和补全的View
View footerViewContainer = mFooterViewInfos.get(position / mNumColumns).viewContainer;
if (position % mNumColumns == 0) {
return footerViewContainer;
} else {
if (convertView == null) {
convertView = new View(parent.getContext());
}
convertView.setVisibility(View.INVISIBLE);
convertView.setMinimumHeight(footerViewContainer.getHeight());
return convertView;
}
}
}
@Override
public int getItemViewType(int position) {
if (mAdapter != null) {
int adapterCount = mAdapter.getCount();
if (position < adapterCount) {
return mAdapter.getItemViewType(position);
} else if (position % mNumColumns == 0) {
return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
} else {
int vacantCount = mNumColumns - adapterCount % mNumColumns;
if (position < (adapterCount + vacantCount)) {
return mAdapter.getViewTypeCount() + 1;
} else {
return mAdapter.getViewTypeCount();
}
}
}
return position % mNumColumns == 0 ? AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER : 1;
}
@Override
public int getViewTypeCount() {
if (mAdapter != null) {
return mAdapter.getViewTypeCount() + 2;
}
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();
}
}
}
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