问题
I am trying to implement a android activity where I have sections of items (for example car brands and their models).
I want to be able to display the items in a grid (e.g. fixed to 3 columns) and each of the grids can be collapsed. Actually I want exactly what the ExpandableList view does for ListViews but with a GridView.
Unfortunately if I return a GridView in the ExpandableListAdapter, the items inside this GridView won't be recycled as they are moving off the screen during scrolling. And we have a lot of items to display which would lead to serious memory issues.
How would I achieve something like that ?
Regards Ben
回答1:
Here's my reinvented wheel (A lot of code is copy-pasted from AOSP's GridView).
package ua.snuk182.expandablegrid;
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.database.DataSetObserver;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Gravity;
import android.view.View;
import android.view.ViewDebug;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.LinearLayout;
public class ExpandableGridView extends ExpandableListView {
/**
* Disables stretching.
*
* @see #setStretchMode(int)
*/
public static final int NO_STRETCH = 0;
/**
* Stretches the spacing between columns.
*
* @see #setStretchMode(int)
*/
public static final int STRETCH_SPACING = 1;
/**
* Stretches columns.
*
* @see #setStretchMode(int)
*/
public static final int STRETCH_COLUMN_WIDTH = 2;
/**
* Stretches the spacing between columns. The spacing is uniform.
*
* @see #setStretchMode(int)
*/
public static final int STRETCH_SPACING_UNIFORM = 3;
/**
* Creates as many columns as can fit on screen.
*
* @see #setNumColumns(int)
*/
public static final int AUTO_FIT = -1;
private int mNumColumns = AUTO_FIT;
private int mHorizontalSpacing = 0;
private int mRequestedHorizontalSpacing;
private int mVerticalSpacing = 0;
private int mStretchMode = STRETCH_COLUMN_WIDTH;
private int mColumnWidth;
private int mRequestedColumnWidth;
private int mRequestedNumColumns;
public ExpandableGridView(Context context) {
this(context, null);
}
public ExpandableGridView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public ExpandableGridView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
TypedArray a = context.obtainStyledAttributes(attrs,
R.styleable.ExpandableGridView, defStyle, 0);
int hSpacing = a.getDimensionPixelOffset(
R.styleable.ExpandableGridView_horizontalSpacing, 0);
setHorizontalSpacing(hSpacing);
int vSpacing = a.getDimensionPixelOffset(
R.styleable.ExpandableGridView_verticalSpacing, 0);
setVerticalSpacing(vSpacing);
int index = a.getInt(R.styleable.ExpandableGridView_stretchMode, STRETCH_COLUMN_WIDTH);
if (index >= 0) {
setStretchMode(index);
}
int columnWidth = a.getDimensionPixelOffset(R.styleable.ExpandableGridView_columnWidth, -1);
if (columnWidth > 0) {
setColumnWidth(columnWidth);
}
int numColumns = a.getInt(R.styleable.ExpandableGridView_numColumns, 1);
setNumColumns(numColumns);
//I haven't dealt with gravity yet, so this is commented for now...
/*index = a.getInt(R.styleable.ExpandableGridView_gravity, -1);
if (index >= 0) {
setGravity(index);
}*/
a.recycle();
}
@Override
public void setAdapter(ExpandableListAdapter adapter) {
super.setAdapter(new ExpandableGridInnerAdapter(adapter));
}
/**
* Set the amount of horizontal (x) spacing to place between each item
* in the grid.
*
* @param horizontalSpacing The amount of horizontal space between items,
* in pixels.
*
* @attr ref android.R.styleable#GridView_horizontalSpacing
*/
public void setHorizontalSpacing(int horizontalSpacing) {
if (horizontalSpacing != mRequestedHorizontalSpacing) {
mRequestedHorizontalSpacing = horizontalSpacing;
requestLayout();
}
}
/**
* Returns the amount of horizontal spacing currently used between each item in the grid.
*
* <p>This is only accurate for the current layout. If {@link #setHorizontalSpacing(int)}
* has been called but layout is not yet complete, this method may return a stale value.
* To get the horizontal spacing that was explicitly requested use
* {@link #getRequestedHorizontalSpacing()}.</p>
*
* @return Current horizontal spacing between each item in pixels
*
* @see #setHorizontalSpacing(int)
* @see #getRequestedHorizontalSpacing()
*
* @attr ref android.R.styleable#GridView_horizontalSpacing
*/
public int getHorizontalSpacing() {
return mHorizontalSpacing;
}
/**
* Returns the requested amount of horizontal spacing between each item in the grid.
*
* <p>The value returned may have been supplied during inflation as part of a style,
* the default GridView style, or by a call to {@link #setHorizontalSpacing(int)}.
* If layout is not yet complete or if GridView calculated a different horizontal spacing
* from what was requested, this may return a different value from
* {@link #getHorizontalSpacing()}.</p>
*
* @return The currently requested horizontal spacing between items, in pixels
*
* @see #setHorizontalSpacing(int)
* @see #getHorizontalSpacing()
*
* @attr ref android.R.styleable#GridView_horizontalSpacing
*/
public int getRequestedHorizontalSpacing() {
return mRequestedHorizontalSpacing;
}
/**
* Set the amount of vertical (y) spacing to place between each item
* in the grid.
*
* @param verticalSpacing The amount of vertical space between items,
* in pixels.
*
* @see #getVerticalSpacing()
*
* @attr ref android.R.styleable#GridView_verticalSpacing
*/
public void setVerticalSpacing(int verticalSpacing) {
if (verticalSpacing != mVerticalSpacing) {
mVerticalSpacing = verticalSpacing;
requestLayout();
}
}
/**
* Returns the amount of vertical spacing between each item in the grid.
*
* @return The vertical spacing between items in pixels
*
* @see #setVerticalSpacing(int)
*
* @attr ref android.R.styleable#GridView_verticalSpacing
*/
public int getVerticalSpacing() {
return mVerticalSpacing;
}
/**
* Control how items are stretched to fill their space.
*
* @param stretchMode Either {@link #NO_STRETCH},
* {@link #STRETCH_SPACING}, {@link #STRETCH_SPACING_UNIFORM}, or {@link #STRETCH_COLUMN_WIDTH}.
*
* @attr ref android.R.styleable#GridView_stretchMode
*/
public void setStretchMode(int stretchMode) {
if (stretchMode != mStretchMode) {
mStretchMode = stretchMode;
requestLayout();
}
}
public int getStretchMode() {
return mStretchMode;
}
/**
* Set the width of columns in the grid.
*
* @param columnWidth The column width, in pixels.
*
* @attr ref android.R.styleable#GridView_columnWidth
*/
public void setColumnWidth(int columnWidth) {
if (columnWidth != mRequestedColumnWidth) {
mRequestedColumnWidth = columnWidth;
requestLayout();
}
}
/**
* Return the width of a column in the grid.
*
* <p>This may not be valid yet if a layout is pending.</p>
*
* @return The column width in pixels
*
* @see #setColumnWidth(int)
* @see #getRequestedColumnWidth()
*
* @attr ref android.R.styleable#GridView_columnWidth
*/
public int getColumnWidth() {
return mColumnWidth;
}
/**
* Return the requested width of a column in the grid.
*
* <p>This may not be the actual column width used. Use {@link #getColumnWidth()}
* to retrieve the current real width of a column.</p>
*
* @return The requested column width in pixels
*
* @see #setColumnWidth(int)
* @see #getColumnWidth()
*
* @attr ref android.R.styleable#GridView_columnWidth
*/
public int getRequestedColumnWidth() {
return mRequestedColumnWidth;
}
/**
* Set the number of columns in the grid
*
* @param numColumns The desired number of columns.
*
* @attr ref android.R.styleable#GridView_numColumns
*/
public void setNumColumns(int numColumns) {
if (numColumns != mRequestedNumColumns) {
mRequestedNumColumns = numColumns;
requestLayout();
}
}
/**
* Get the number of columns in the grid.
* Returns {@link #AUTO_FIT} if the Grid has never been laid out.
*
* @attr ref android.R.styleable#GridView_numColumns
*
* @see #setNumColumns(int)
*/
@ViewDebug.ExportedProperty
public int getNumColumns() {
return mNumColumns;
}
public ExpandableListAdapter getInnerAdapter() {
return ((ExpandableGridInnerAdapter)getExpandableListAdapter()).mInnerAdapter;
}
private boolean determineColumns(int availableSpace) {
final int requestedHorizontalSpacing = mRequestedHorizontalSpacing;
final int stretchMode = mStretchMode;
final int requestedColumnWidth = mRequestedColumnWidth;
boolean didNotInitiallyFit = false;
if (mRequestedNumColumns == AUTO_FIT) {
if (requestedColumnWidth > 0) {
// Client told us to pick the number of columns
mNumColumns = (availableSpace + requestedHorizontalSpacing) /
(requestedColumnWidth + requestedHorizontalSpacing);
} else {
// Just make up a number if we don't have enough info
mNumColumns = 2;
}
} else {
// We picked the columns
mNumColumns = mRequestedNumColumns;
}
if (mNumColumns <= 0) {
mNumColumns = 1;
}
switch (stretchMode) {
case NO_STRETCH:
// Nobody stretches
mColumnWidth = requestedColumnWidth;
mHorizontalSpacing = requestedHorizontalSpacing;
break;
default:
int spaceLeftOver = availableSpace - (mNumColumns * requestedColumnWidth) -
((mNumColumns - 1) * requestedHorizontalSpacing);
if (spaceLeftOver < 0) {
didNotInitiallyFit = true;
}
switch (stretchMode) {
case STRETCH_COLUMN_WIDTH:
// Stretch the columns
mColumnWidth = requestedColumnWidth + spaceLeftOver / mNumColumns;
mHorizontalSpacing = requestedHorizontalSpacing;
break;
case STRETCH_SPACING:
// Stretch the spacing between columns
mColumnWidth = requestedColumnWidth;
if (mNumColumns > 1) {
mHorizontalSpacing = requestedHorizontalSpacing +
spaceLeftOver / (mNumColumns - 1);
} else {
mHorizontalSpacing = requestedHorizontalSpacing + spaceLeftOver;
}
break;
case STRETCH_SPACING_UNIFORM:
// Stretch the spacing between columns
mColumnWidth = requestedColumnWidth;
if (mNumColumns > 1) {
mHorizontalSpacing = requestedHorizontalSpacing +
spaceLeftOver / (mNumColumns + 1);
} else {
mHorizontalSpacing = requestedHorizontalSpacing + spaceLeftOver;
}
break;
}
break;
}
return didNotInitiallyFit;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
if (widthMode == MeasureSpec.UNSPECIFIED) {
if (mColumnWidth > 0) {
widthSize = mColumnWidth + getPaddingLeft() + getPaddingRight();
} else {
widthSize = getPaddingLeft() + getPaddingRight();
}
widthSize += getVerticalScrollbarWidth();
}
int childWidth = widthSize - getPaddingLeft() - getPaddingRight();
determineColumns(childWidth);
}
private class ExpandableGridInnerAdapter implements ExpandableListAdapter {
private final ExpandableListAdapter mInnerAdapter;
private ExpandableGridInnerAdapter(ExpandableListAdapter adapter) {
this.mInnerAdapter = adapter;
}
@Override
public int getGroupCount() {
return mInnerAdapter.getGroupCount();
}
@Override
public int getChildrenCount(int groupPosition) {
int realCount = mInnerAdapter.getChildrenCount(groupPosition);
int count;
if (mNumColumns != AUTO_FIT) {
count = realCount > 0 ? (realCount + mNumColumns - 1) / mNumColumns : 0;
} else {
count = realCount;
}
return count;
}
@Override
public Object getGroup(int groupPosition) {
return mInnerAdapter.getGroup(groupPosition);
}
@Override
public Object getChild(int groupPosition, int childPosition) {
return mInnerAdapter.getChild(groupPosition, childPosition);
}
@Override
public long getGroupId(int groupPosition) {
return mInnerAdapter.getGroupId(groupPosition);
}
@Override
public long getChildId(int groupPosition, int childPosition) {
return 0;
}
@Override
public boolean hasStableIds() {
return false;
}
@Override
public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
return mInnerAdapter.getGroupView(groupPosition, isExpanded, convertView, parent);
}
@SuppressLint("InlinedApi")
@Override
public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
LinearLayout row = (LinearLayout) (convertView != null ? convertView : new LinearLayout(getContext()));
if (row.getLayoutParams() == null) {
row.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT, AbsListView.ITEM_VIEW_TYPE_IGNORE));
row.setPadding(0, mVerticalSpacing / 2, 0, mVerticalSpacing / 2);
row.setGravity(Gravity.CENTER_HORIZONTAL);
}
int groupChildrenCount = mInnerAdapter.getChildrenCount(groupPosition);
int index = 0;
for (int i=mNumColumns * childPosition; i<(mNumColumns * (childPosition + 1)); i++, index++) {
View child;
View cachedChild = index < row.getChildCount() ? row.getChildAt(index) : null;
if (i<groupChildrenCount) {
if (cachedChild != null && cachedChild.getTag() == null) {
((ViewGroup)cachedChild.getParent()).removeView(cachedChild);
cachedChild = null;
}
child = mInnerAdapter.getChildView(groupPosition, i, i == (groupChildrenCount - 1), cachedChild, parent);
child.setTag(mInnerAdapter.getChild(groupPosition, i));
} else {
if (cachedChild != null && cachedChild.getTag() != null) {
((ViewGroup)cachedChild.getParent()).removeView(cachedChild);
cachedChild = null;
}
child = new View(getContext());
child.setTag(null);
}
if (!(child.getLayoutParams() instanceof LinearLayout.LayoutParams)) {
LinearLayout.LayoutParams params;
if (child.getLayoutParams() == null) {
params = new LinearLayout.LayoutParams(mColumnWidth, LayoutParams.WRAP_CONTENT, 1);
} else {
params = new LinearLayout.LayoutParams(mColumnWidth, child.getLayoutParams().height, 1);
}
child.setLayoutParams(params);
}
child.setPadding(mHorizontalSpacing / 2, 0, mHorizontalSpacing / 2, 0);
if (index == row.getChildCount()) {
row.addView(child, index);
} else {
child.invalidate();
}
}
return row;
}
@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
return false;
}
@Override
public void registerDataSetObserver(DataSetObserver observer) {
mInnerAdapter.registerDataSetObserver(observer);
}
@Override
public void unregisterDataSetObserver(DataSetObserver observer) {
mInnerAdapter.unregisterDataSetObserver(observer);
}
@Override
public boolean areAllItemsEnabled() {
return mInnerAdapter.areAllItemsEnabled();
}
@Override
public boolean isEmpty() {
return mInnerAdapter.isEmpty();
}
@Override
public void onGroupExpanded(int groupPosition) {
mInnerAdapter.onGroupExpanded(groupPosition);
}
@Override
public void onGroupCollapsed(int groupPosition) {
mInnerAdapter.onGroupCollapsed(groupPosition);
}
/*@Override
public long getCombinedChildId(long groupId, long childId) {
return mInnerAdapter.getCombinedChildId(groupId, childId);
}
@Override
public long getCombinedGroupId(long groupId) {
return mInnerAdapter.getCombinedGroupId(groupId);
}*/
public long getCombinedChildId(long groupId, long childId) {
return 0x8000000000000000L | ((groupId & 0x7FFFFFFF) << 32) | (childId & 0xFFFFFFFF);
}
public long getCombinedGroupId(long groupId) {
return (groupId & 0x7FFFFFFF) << 32;
}
}
}
Corresponding attrs.xml.
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="ExpandableGridView">
<attr name="horizontalSpacing" format="dimension" />
<attr name="verticalSpacing" format="dimension" />
<attr name="stretchMode">
<enum name="none" value="0"/>
<enum name="spacingWidth" value="1" />
<enum name="columnWidth" value="2" />
<enum name="spacingWidthUniform" value="3" />
</attr>
<attr name="columnWidth" format="dimension" />
<attr name="numColumns" format="integer" min="0">
<enum name="auto_fit" value="-1" />
</attr>
</declare-styleable>
</resources>
回答2:
instead of using multiple expandable gridviews you could use this library https://github.com/TonicArtos/StickyGridHeaders, in which you can put one adapter with one gridView (the custom StickyGridHeadersView), and manage the different headers with specific view handlers for each kind of header/grid-element
回答3:
You can use this example of Expandable RecyclerView . It provides an Expandable RecyclerView with group items that can be individually expanded to show its children in a two-dimensional scrolling grid. Each grid item can be selected.
来源：https://stackoverflow.com/questions/19875903/expandable-gridview-with-view-recycling-in-android