可以折叠Gridview

本文主要是介绍可以折叠Gridview，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

可以折叠Gridview

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实现原理

1、折叠实现

重写gridview的setAdapter方法

    @Override
public void setAdapter(ListAdapter adapter) {if (foldNm > 0) {//进行折叠adapter = new FoldViewGridAdapter(adapter, foldNm);}super.setAdapter(adapter);}

FoldViewGridAdapter是一个包装类，用来实现对当前的adapter包装，主要是重写getCount方法如下:

private class FoldViewGridAdapter implements WrapperListAdapter {...@Overridepublic int getCount() {//fn如果小于1，不进行折叠,根据是否折叠来判断,默认是折叠状态if (fn < 0) {return adapter.getCount();} else {//如果fn大于0，进行折叠处理if (expend) {return adapter.getCount();} else {return Math.min(adapter.getCount(), fn * getNumColumns());}}}@Overridepublic ListAdapter getWrappedAdapter() {return this;}...
}

先判断fn,也就是折叠后显示的行数，fn初始值为-1，也就是不折叠，当设置了fn值大于0，那么就需要进行折叠判断，如果需要折叠，则返回

 return Math.min(adapter.getCount(), fn * getNumColumns());

两者中的最小值。fn * getNumColumns()是折叠时显示的行数和显示的列数的积，也就是显示的个数。

2、如何添加ExpendControlView

同样在重写setAdapter方法，对adapter进行再次封装。

HeaderViewGridAdapter headerViewGridAdapter = new HeaderViewGridAdapter(mHeaderViewInfos, mFooterViewInfos, adapter);

添加ExpendControlView的逻辑主要在HeaderViewGridAdapter中，HeaderViewGrideAdapter要实现一下几点：

1、怎么使添加的ExpendControlView，独占一行。

    public void addExpendControlView(View v, Object data, boolean isSelectable, boolean isExpendControlView) {ViewGroup.LayoutParams lyp = v.getLayoutParams();FixedViewInfo info = new FixedViewInfo();FrameLayout fl = new FullWidthFixedViewLayout(getContext());if (lyp != null) {v.setLayoutParams(new FrameLayout.LayoutParams(lyp.width, lyp.height));fl.setLayoutParams(new LayoutParams(lyp.width, lyp.height));}fl.addView(v);info.view = v;info.viewContainer = fl;info.data = data;info.isSelectable = isSelectable;//控制是否可以折叠info.isExpendControlView = isExpendControlView;mFooterViewInfos.add(info);if (mAdapter != null) {((HeaderViewGridAdapter) mAdapter).notifyDataSetChanged();}}

在addExpendControlView方法中，会先创建一个fl的viewGroup,然后再把controlview添加到fl中，FullWidthFixedViewLayout的代码如下：

    private class FullWidthFixedViewLayout extends FrameLayout {public FullWidthFixedViewLayout(Context context) {super(context);}@Overrideprotected void onLayout(boolean changed, int left, int top, int right, int bottom) {int realLeft = GridViewEnableFooter.this.getPaddingLeft() + getPaddingLeft();// Try to make where it should be, from left, full widthif (realLeft != left) {offsetLeftAndRight(realLeft - left);}super.onLayout(changed, left, top, right, bottom);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {int targetWidth = GridViewEnableFooter.this.getMeasuredWidth()- GridViewEnableFooter.this.getPaddingLeft()- GridViewEnableFooter.this.getPaddingRight();widthMeasureSpec = MeasureSpec.makeMeasureSpec(targetWidth,MeasureSpec.getMode(widthMeasureSpec));super.onMeasure(widthMeasureSpec, heightMeasureSpec);}}

在onLayout和onMeasure的时候设置宽度和gridview的宽度一致，来设置fl的宽度和gridview的宽度一致，这样可以独占一行。

2、添加ExpendControlView后count的计算。

添加ExpendControlView需要重新计算adapter的getcount返回值，getCount方法如下：

        public int getCount() {return getExpendControlViewsCount() * mNumColumns + getAdapterAndPlaceHolderCount();}

因为一个ExpendControlView会占一行，所以需要乘以列数，getAdapterAndPlaceHolderCount方法实现如下：

        private int getAdapterAndPlaceHolderCount() {return (int) (Math.ceil(1f * mAdapter.getCount() / mNumColumns) * mNumColumns);}

getAdapterAndPlaceHolderCount用来补充数量，使得count个数为整数列的倍数。如果不是整数列，那么添加的ExpendControlView不会占用单独的行，显示有问题。

3、重写getView方法。

添加的ExpendControlView需要在getView中进行返回，所以还需要重写getView方法。

public View getView(int position, View convertView, ViewGroup parent) {// Adapterfinal int adjPosition = position - numHeadersAndPlaceholders;int adapterCount = 0;if (mAdapter != null) {adapterCount = getAdapterAndPlaceHolderCount();if (adjPosition < adapterCount) {if (adjPosition < mAdapter.getCount()) {return mAdapter.getView(adjPosition, convertView, parent);} else {if (convertView == null) {convertView = new View(parent.getContext());}convertView.setVisibility(View.INVISIBLE);convertView.setMinimumHeight(mRowHeight);return convertView;}}}// ExpendControlViewfinal int footerPosition = adjPosition - adapterCount;if (footerPosition < getCount()) {View footViewContainer = mFooterViewInfos.get(footerPosition / mNumColumns).viewContainer;if (position % mNumColumns == 0) {return footViewContainer;} 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(footViewContainer.getHeight());return convertView;}}throw new ArrayIndexOutOfBoundsException(position);}

方法

1、添加底部控制view

public void addExpendControlView(View view)

2、设置折叠时展示的行数

setFoldNum(int foldNm)

用于设置折叠时显示的行数

使用方法

//折叠控制view
gridView.addFooterView(LoadMoreView(this))//设置折叠行数
gridView.setFoldNum(2)gridView.adapter = object : BaseAdapter() {...}

上面的loadMoreView就是底部的折叠控制view，添加自己的控制view时，继承下面接口

interface IExpendControl {/*** 展开*/fun expend()/*** 折叠*/fun fold()
}

重写expend和fold方法，也就是展开和折叠，完成控制。

class LoadMoreView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null
) : ConstraintLayout(context, attrs), IExpendControl {private var viewBinding: LoadMoreViewBinding =LoadMoreViewBinding.inflate(LayoutInflater.from(context), this)override fun expend() {//展开时操作viewBinding.loadMore.text = "收起"viewBinding.arrow.setImageResource(R.drawable.up_arrow)}override fun fold() {//折叠时操作viewBinding.loadMore.text = "展开全部"viewBinding.arrow.setImageResource(R.drawable.down_arrow)}
}