Android項目：模仿ConvertView原理(ListView的getView方法)對View對象進行回收和複用

時間  2020-01-18
標籤 android 項目 模仿 convertview 原理 listview getview 方法 view 對象 進行 回收 欄目 Android 简体版
原文   原文鏈接

  在項目優化過程當中,經過MAT監控發現存在一處內存泄露,反覆進入某個頁面,內存佔用愈來愈大。後分析找到了泄露緣由,原來是在自定義列表中,將行佈局的layout文件inflate成view對象的時候,每加載一次列表就要new出一組新的view對象。由於沒有對這些佈局一致的view進行復用,又無法及時釋放,致使了列表的行佈局對象越積越多,形成內存泄露。
java

  解決這個oom問題,首先想到了listview加載中對convertview的回收和複用的方法。因而模仿convertview的原理寫了個對view對象進行回收和複用的類,此處類名爲ViewRecycler,使用後有效的解決了view對象的複用,遠離這個棘手的oom問題。因爲項目中須要複用的view對象佈局都是同樣的,此方法只考慮了複用同一佈局的狀況。同時,項目中的列表已有獲取顯示行與隱藏行的相應接口,此方法僅主要從回收與複用的邏輯層面加以實現,並未涉及任何底層代碼部分。數組


1、如下是具體的實現過程:ide


1.首先ViewRecycler類須要兩個容器分別用來保存活動的View對象和回收可複用的View對象。一個map用來保存回收的View(無序添加),一個數組用來記錄當前顯示的行號以及對應的View(有序添加)。佈局

以下:性能

private SparseArray<View> recycleViews;// 廢棄的view
private View[] activeViews = new View[0];//正在使用的view


注:key爲int類型的HashMap用SparseArray代替,會有更好的性能.優化


2.每次列表刷新或變化,就更新一次activeViews的大小。即activeViews的數組長度與當前列表的總行數一致。在刷新列表或者加載更多時,調用getCount()方法更新activeViews數組長度。this

以下:spa

// 加載完畢
private void loadComplete()
{
    //.....
    mViewRecycler.getCount(mDataList.size());
}


ViewRecycler類裏的getCount方法:調試

    /** 獲取活動view的總數 */
    public void getCount(int count)
    {
        final int length = this.activeViews.length;
        if (count > length)
        {
            final View[] activeViews = this.activeViews;
            this.activeViews = Arrays.copyOf(activeViews, count);
                                                                                                                                                                                                                                                                                                                                                                         
//            Log.e("getCount", "activeViews[" + (count - 1) + "]=" + this.activeViews[count-1]);
        }
    }


3.列表每新增顯示一行,就先獲取是否有可複用的View對象。先判斷recycleViews是否已存有該行號對應的View,沒有則獲取最新回收的View。再結合setTag與getTag即可實現對回收View對象的複用了。若是recycleViews沒有可複用的View,則inflate生成新的View。code

以下:

public void convertFromView(final ListJson listJson, final int n)
{
    ViewHolder holder = null;
                                                                                                                                                                                                                                                                                                                 
    // 判斷是否有可重複利用的view
    View resycleView = mViewRecycler.getRecycleView(n);
                                                                                                                                                                                                                                                                                                                 
    if (resycleView == null)
    {
        resycleView = LayoutInflater.from(getActivity()).inflate(R.layout.list_item, null);
                                                                                                                                                                                                                                                                                                                     
        holder = new ViewHolder();
        //.....
        holder.iv_main = (ImageView) resycleView.findViewById(R.id.item_iv_main);
                                                                                                                                                                                                                                                                                                                     
        resycleView.setTag(holder);
    }
    else
    {
        holder = (ViewHolder) resycleView.getTag();
    }
                                                                                                                                                                                                                                                                                                                 
    //保存新增活動的View對象
    mViewRecycler.addActiveView(n, resycleView);
                                                                                                                                                                                                                                                                                                                 
    // 加載行佈局數據
    holder.tv_title.setText(lison.getName());
    holder.tv_price.setText("待定");
    //.....
                                                                                                                                                                                                                                                                                                                 
    // 下載圖片
    ImageLoadingListener listener = new ImageLoadingListener()
    {
        @Override
        public void onLoadingStarted(String arg0, View arg1)
        {
        }
                                                                                                                                                                                                                                                                                                                     
        @Override
        public void onLoadingComplete(String arg0, View arg1, Bitmap bitmap)
        {
            //獲取view對象
            View bitmapView = mViewRecycler.getActiveView(n);
            if (bitmapView != null)
            {
                ViewHolder holder = (ViewHolder) bitmapView.getTag();
                if (holder != null)
                {
                    // 加載圖片
                    holder.iv_main.setImageBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.bg_item));
                }
            }
        }
                                                                                                                                                                                                                                                                                                                     
        @Override
        public void onLoadingFailed(String arg0, View arg1, FailReason arg2)
        {
        }
                                                                                                                                                                                                                                                                                                                     
        @Override
        public void onLoadingCancelled(String arg0, View arg1)
        {
        }
    };
    p_w_picpathLoader.loadImage(listJson.getStatusPic(), listener);
}


ViewRecycler類裏的對應方法:

(1)將行號與對應的View填充到activeViews數組裏保存。添加前對行號與activeViews的長度進行校訂,避免越界。

    /** 添加記錄當前活動的view */
    public void addActiveView(int position, View view)
    {
        final int length = this.activeViews.length;
        if (position > length - 1)
        {
            getCount(position + 1);
        }
        this.activeViews[position] = view;
                                                                                                                                                                                                                                                                                      
//        Log.e("addActiveView", "activeViews.size() = " + Arrays.toString(activeViews));
    }


(2)根據行號獲取對應的View對象。

/** 獲取某個活動view */
public View getActiveView(int position)
{
    final int length = this.activeViews.length;
    if (position > length - 1)
    {
        getCount(position + 1);
    }
    return activeViews[position];
}


(3)獲取已回收的View對象。

/** 獲取回收的view */
View getRecycleView(int position)
{
    return retrieveFromRecycle(recycleViews, position);
}
/** 檢索回收的view */
static View retrieveFromRecycle(SparseArray<View> recycleViews, int position)
{
    int size = recycleViews.size();
    if (size > 0)
    {
        // See if we still have a view for this position.
        for (int i = 0; i < size; i++)
        {
            int fromPosition = recycleViews.keyAt(i);
            View view = recycleViews.get(fromPosition);
            if (fromPosition == position)
            {
                recycleViews.remove(fromPosition);
                return view;
            }
        }
        int index = size - 1;
        View r = recycleViews.valueAt(index);
        recycleViews.remove(recycleViews.keyAt(index));
        return r;
    }
    else
    {
        return null;
    }
}


4.列表每隱藏一行,將消失的行佈局對應的View對象回收,添加到recycleViews容器裏,同時移除activeViews裏的這個View。而後再進行比較並清除recycleViews容器裏的回收對象,保證回收對象總數很少於活動view容器的總長度。

以下:

// 隱藏
@Override
public void onInvalidateItem(int id)
{
    super.onInvalidateItem(id);
    // .....
                                                                                                                                                                                         
                                                                                                                                                                                         
    // 回收view對象
    View recycleView = mViewRecycler.getActiveView(id);
    if (recycleView != null)
    {
        mViewRecycler.addRecycleView(id, recycleView);
    }
                                                                                                                                                                                         
}


ViewRecycler類裏的對應方法:

    /** 添加廢棄的view,無序添加 */
    void addRecycleView(int position, View scrap)
    {
        recycleViews.put(position, scrap);
                                                                                                                                                                                                     
        final int length = this.activeViews.length;
        if (position < length)
        {
            this.activeViews[position] = null;
        }
        pruneRecycleViews();
//        Log.e("Recycle", "Recycle.size() = " +recycleViews.size());
    }


/** 確保廢棄的view總數很少於活動的view容器的長度(此方法可再改進爲很少於當前活動的View對象數量) */
private void pruneRecycleViews()
{
    final int maxViews = activeViews.length;
    int size = recycleViews.size();
    final int extras = size - maxViews;
    size--;
    for (int j = 0; j < extras; j++)
    {
        recycleViews.remove(recycleViews.keyAt(size--));
    }
}


5.退出時,清除全部View對象及其引用。

如下方法則是根據項目需求,將全部的活動view移到recycleViews裏,再整理recycleViews。

以下：

@Override
public void onDestroy()
{
    super.onDestroy();
    //銷燬全部view對象
    mViewRecycler.recycleAllActiveViews();
}


ViewRecycler類裏的對應方法:

/** 將全部剩餘的活動view移到廢棄view裏 */
void recycleAllActiveViews()
{
    final View[] activeViews = this.activeViews;
    SparseArray<View> recycleViews = this.recycleViews;
    final int count = activeViews.length;
    for (int i = count - 1; i >= 0; i--)
    {
        final View victim = activeViews[i];
        if (victim != null)
        {
            activeViews[i] = null;
            recycleViews.put(i, victim);
        }
    }
                                                                                                                                                                         
    pruneRecycleViews();
}



2、調試結果

滑動時,請求加載行數據。每次添加一個行佈局對象，當達到10行後開始執行View對象回收。每次將棧底的View回收並複用到棧頂的行佈局裏。以下圖:

wKioL1MT8iTS8UokAAbh95qOXfU070.jpg

wKiom1MT8kqy3pXUAAIx3_1C-iQ550.jpg



3、最後附上完整的ViewRecycler類

以下:

public class ViewRecycler
{
    private SparseArray<View> recycleViews;// 廢棄的view
    private View[] activeViews = new View[0];//正在使用的view
                                                
    public ViewRecycler()
    {
        recycleViews = new SparseArray<View>();
    }
                                             
    /** 獲取活動view的總數 */
    public void getCount(int count)
    {
        final int length = this.activeViews.length;
        if (count > length)
        {
            final View[] activeViews = this.activeViews;
            this.activeViews = Arrays.copyOf(activeViews, count);
                                                        
//            Log.e("getCount", "activeViews[" + (count - 1) + "]=" + this.activeViews[count-1]);
        }
    }
                                                
    /** 添加記錄當前活動的view */
    public void addActiveView(int position, View view)
    {
        final int length = this.activeViews.length;
        if (position > length - 1)
        {
            getCount(position + 1);
        }
        this.activeViews[position] = view;
                                                    
//        Log.e("addActiveView", "activeViews.size() = " + Arrays.toString(activeViews));
    }
                                                
    /** 獲取某個活動view */
    public View getActiveView(int position)
    {
        final int length = this.activeViews.length;
        if (position > length - 1)
        {
            getCount(position + 1);
        }
        return activeViews[position];
    }
                                                
    /** 獲取廢棄的view */
    View getRecycleView(int position)
    {
        return retrieveFromRecycle(recycleViews, position);
    }
                                                
    /** 檢索廢棄的view */
    static View retrieveFromRecycle(SparseArray<View> recycleViews, int position)
    {
        int size = recycleViews.size();
        if (size > 0)
        {
            // See if we still have a view for this position.
            for (int i = 0; i < size; i++)
            {
                int fromPosition = recycleViews.keyAt(i);
                View view = recycleViews.get(fromPosition);
                if (fromPosition == position)
                {
                    recycleViews.remove(fromPosition);
                    return view;
                }
            }
            int index = size - 1;
            View r = recycleViews.valueAt(index);
            recycleViews.remove(recycleViews.keyAt(index));
            return r;
        }
        else
        {
            return null;
        }
    }
                                                
    /** 添加廢棄的view,無序添加 */
    void addRecycleView(int position, View scrap)
    {
        recycleViews.put(position, scrap);
                                                    
        final int length = this.activeViews.length;
        if (position < length)
        {
            this.activeViews[position] = null;
        }
        pruneRecycleViews();
//        Log.e("Recycle", "Recycle.size() = " +recycleViews.size());
    }
                                                
    /** 將全部剩餘的活動view移到廢棄view裏 */
    void recycleAllActiveViews()
    {
        final View[] activeViews = this.activeViews;
        SparseArray<View> recycleViews = this.recycleViews;
        final int count = activeViews.length;
        for (int i = count - 1; i >= 0; i--)
        {
            final View victim = activeViews[i];
            if (victim != null)
            {
                activeViews[i] = null;
                recycleViews.put(i, victim);
            }
        }
                                                    
        pruneRecycleViews();
    }
                                                
    /** 確保廢棄的view很少於活動的view容器的總數量 */
    private void pruneRecycleViews()
    {
        final int maxViews = activeViews.length;
        int size = recycleViews.size();
        final int extras = size - maxViews;
        size--;
        for (int j = 0; j < extras; j++)
        {
            recycleViews.remove(recycleViews.keyAt(size--));
        }
    }
                                                
}


    方法僅供參考，具體實現過程還需根據項目實際需求進行修改或優化。歡迎各路高手不吝賜教,多多交流！


參考資料:


轉載請註明出處：http://glblong.blog.51cto.com/3058613/1366319

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