[Android]ListView性能优化之视图缓存-移动端开发-火龙果软件工程

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[Android]ListView性能优化之视图缓存

作者：农民伯伯来源：博客园发布于 2015-6-10

2312 次浏览

前言

ListView是Android中最常用的控件，通过适配器来进行数据适配然后显示出来，而其性能是个很值得研究的话题。本文与你一起探讨Google I/O提供的优化Adapter方案，欢迎大家交流。

正文

一、准备

1.1了解关于Google IO大会关于Adapter的优化，参考以下文章：

Android开发之ListView 适配器（Adapter）优化

Android开发——09Google I/O之让Android UI性能更高效(1)

PDF下载：Google IO.pdf

1.2准备测试代码：

Activity

private TestAdapter mAdapter;

    private String[] mArrData;
    private TextView mTV;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mTV = (TextView) findViewById(R.id.tvShow);

        mArrData = new String[1000];
        for (int i = 0; i < 1000; i++) {
            mArrData[i] = "Google IO Adapter" + i;
        }
        mAdapter = new TestAdapter(this, mArrData);
        ((ListView) findViewById(android.R.id.list)).setAdapter(mAdapter);
    }

代码说明：模拟一千条数据，TestAdapter继承自BaseAdapter，main.xml见文章末尾下载。

二、测试

测试方法：手动滑动ListView至position至50然后往回滑动，充分利用convertView不等于null的代码段。

2.1方案一

按照Google I/O介绍的第二种方案，把item子元素分别改为4个和10个，这样效果更佳明显。

2.1.1测试代码

private int count = 0;
        private long sum = 0L;
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            //开始计时
            long startTime = System.nanoTime();
            
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_icon_text,
                        null);
            }
            ((ImageView) convertView.findViewById(R.id.icon1)).setImageResource(R.drawable.icon);
            ((TextView) convertView.findViewById(R.id.text1)).setText(mData[position]);
            ((ImageView) convertView.findViewById(R.id.icon2)).setImageResource(R.drawable.icon);
            ((TextView) convertView.findViewById(R.id.text2)).setText(mData[position]);
            
            //停止计时
            long endTime = System.nanoTime();
            //计算耗时
            long val = (endTime - startTime) / 1000L;
            Log.e("Test", "Position:" + position + ":" + val);
            if (count < 100) {
                if (val < 1000L) {
                    sum += val;
                    count++;
                }
            } else
                mTV.setText(String.valueOf(sum / 100L));//显示统计结果
            return convertView;
        }

2.1.2　　测试结果（微秒除以1000，见代码）

2.2方案二

按照Google I/O介绍的第三种方案，是把item子元素分别改为4个和10个。

2.2.1测试代码

private int count = 0;
        private long sum = 0L;

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // 开始计时
            long startTime = System.nanoTime();

            ViewHolder holder;
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_icon_text,
                        null);
                holder = new ViewHolder();
                holder.icon1 = (ImageView) convertView.findViewById(R.id.icon1);
                holder.text1 = (TextView) convertView.findViewById(R.id.text1);
                holder.icon2 = (ImageView) convertView.findViewById(R.id.icon2);
                holder.text2 = (TextView) convertView.findViewById(R.id.text2);
                convertView.setTag(holder);
            }
            else{
                holder = (ViewHolder)convertView.getTag();
            }
            holder.icon1.setImageResource(R.drawable.icon);
            holder.text1.setText(mData[position]);
            holder.icon2 .setImageResource(R.drawable.icon);
            holder.text2.setText(mData[position]);

            // 停止计时
            long endTime = System.nanoTime();
            // 计算耗时
            long val = (endTime - startTime) / 1000L;
            Log.e("Test", "Position:" + position + ":" + val);
            if (count < 100) {
                if (val < 1000L) {
                    sum += val;
                    count++;
                }
            } else
                mTV.setText(String.valueOf(sum / 100L));// 显示统计结果
            return convertView;
        }
    }

    static class ViewHolder {
        TextView text1;
        ImageView icon1;
        TextView text2;
        ImageView icon2;
    }

2.2.2　　测试结果（微秒除以1000，见代码）

2.3方案三

此方案为“Henry Hu”提示，API Level 4以上提供，这里顺带测试了一下不使用静态内部类情况下性能。

2.3.1测试代码

@Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // 开始计时
            long startTime = System.nanoTime();

            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
                convertView.setTag(R.id.icon1, convertView.findViewById(R.id.icon1));
                convertView.setTag(R.id.text1, convertView.findViewById(R.id.text1));
                convertView.setTag(R.id.icon2, convertView.findViewById(R.id.icon2));
                convertView.setTag(R.id.text2, convertView.findViewById(R.id.text2));
            }
            ((ImageView) convertView.getTag(R.id.icon1)).setImageResource(R.drawable.icon);
            ((ImageView) convertView.getTag(R.id.icon2)).setImageResource(R.drawable.icon);
            ((TextView) convertView.getTag(R.id.text1)).setText(mData[position]);
            ((TextView) convertView.getTag(R.id.text2)).setText(mData[position]);

            // 停止计时
            long endTime = System.nanoTime();
            // 计算耗时
            long val = (endTime - startTime) / 1000L;
            Log.e("Test", "Position:" + position + ":" + val);
            if (count < 100) {
                if (val < 1000L) {
                    sum += val;
                    count++;
                }
            } else
                mTV.setText(String.valueOf(sum / 100L) + ":" + nullcount);// 显示统计结果
            return convertView;
        }

2.3.2测试结果（微秒除以1000，见代码）

第一次：450

第二次：467

第三次：472

第四次：451

第五次：441

四、总结

4.1首先有一个认识是错误的，我们先来看截图：

可以发现，只有第一屏（可视范围）调用getView所消耗的时间远远多于后面的，通过对convertView == null内代码监控也是同样的结果。也就是说ListView仅仅缓存了可视范围内的View，随后的滚动都是对这些View进行数据更新。不管你有多少数据，他都只用ArrayList缓存可视范围内的View，这样保证了性能，也造成了我以为ListView只缓存View结构不缓存数据的假相（不会只有我一人这么认为吧- - #）。这也能解释为什么GOOGLE优化方案一比二高很多的原因。那么剩下的也就只有findViewById比较耗时了。据此大家可以看看AbsListView的源代码，看看
obtainView这个方法内的代码及RecycleBin这个类的实现，欢迎分享。

此外了解这个原理了，那么以下代码不运行你可能猜到结果了：

if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
                ((ImageView) convertView.findViewById(R.id.icon1)).setImageResource(R.drawable.icon);
                ((TextView) convertView.findViewById(R.id.text1)).setText(mData[position]);
                ((ImageView) convertView.findViewById(R.id.icon2)).setImageResource(R.drawable.icon);
                ((TextView) convertView.findViewById(R.id.text2)).setText(mData[position]);
            }
            else
                return convertView;

没错，你会发现滚动时会重复显示第一屏的数据！

子控件里的事件因为是同一个控件，也可以直接放到convertView == null 代码块内部，如果需要交互数据比如position，可以通过tag方式来设置并获取当前数据。

4.2本文方案一与方案二对比

这里推荐如果只是一般的应用（一般指子控件不多），无需都是用静态内部类来优化，使用第二种方案即可；反之，对性能要求较高时可采用。此外需要提醒的是这里也是用空间换时间的做法，View本身因为setTag而会占用更多的内存，还会增加代码量；而findViewById会临时消耗更多的内存，所以不可盲目使用，依实际情况而定。

4.3方案三

此方案为“Henry Hu”提示，API Level 4以上支持，原理和方案三一致，减少findViewById次数，但是从测试结果来看效果并不理想，这里不再做进一步的测试。

结束

对于Google I/O大会这个优化方案一直抱迟疑态度，此番测试总算是有了更进一步的了解，欢迎大家先测试后交流，看看还有什么办法能够再优化一点。

一、新浪微博

1.1截图

1.2反编译后相关代码

HomeListActivity

public View getView(int paramInt, View paramView, ViewGroup paramViewGroup)
    {
      int i = --paramInt;
      int j = -1;
      if (i == j);
      for (Object localObject1 = HomeListActivity.this.getReloadView(); ;
 localObject1 = HomeListActivity.this.getLoadMoreView())
      {
        label26: return localObject1;
        int k = HomeListActivity.this.mList.size();
        int l = paramInt;
        int i1 = k;
        if (l != i1)
          break;
      }
      boolean bool1 = true;
      boolean bool2 = null;
      String str1;
      label110: Object localObject2;
      if (StaticInfo.mUser == null)
      {
        List localList1 = HomeListActivity.this.mList;
        int i2 = paramInt;
        str1 = ((MBlog)localList1.get(i2)).uid;
        List localList2 = HomeListActivity.this.mList;
        int i3 = paramInt;
        String str2 = ((MBlog)localList2.get(i3)).uid;
        String str3 = str1;
        if (!str2.equals(str3))
          break label271;
        int i4 = 1;
        label156: if (paramView != null)
          break label277;
        HomeListActivity localHomeListActivity1 = HomeListActivity.this;
        ListView localListView1 = HomeListActivity.this.mLvHome;
        List localList3 = HomeListActivity.this.mList;
        int i5 = paramInt;
        MBlog localMBlog1 = (MBlog)localList3.get(i5);
        HomeListActivity localHomeListActivity2 = HomeListActivity.this;
        int i6 = paramInt;
        boolean bool4 = localHomeListActivity2.isNewCommer(i6);
        int i7 = HomeListActivity.this.mReadMode;
        localObject2 = new MBlogListItemView(localHomeListActivity1, 
localListView1, localMBlog1, bool1, bool2, i4, bool4, i7);
      }
      while (true)
      {
        localObject1 = localObject2;
        break label26:
        str1 = StaticInfo.mUser.uid;
        break label110:
        label271: boolean bool3 = null;
        break label156:
        label277: localObject2 = paramView;
        try
        {
          MainListItemView localMainListItemView = (MainListItemView)localObject2;
          List localList4 = HomeListActivity.this.mList;
          int i8 = paramInt;
          Object localObject3 = localList4.get(i8);
          HomeListActivity localHomeListActivity3 = HomeListActivity.this;
          int i9 = paramInt;
          boolean bool5 = localHomeListActivity3.isNewCommer(i9);
          int i10 = HomeListActivity.this.mReadMode;
          boolean bool6 = bool1;
          boolean bool7 = bool2;
          localMainListItemView.update(localObject3, bool6, bool7, bool5, i10);
        }
        catch (Exception localException)
        {
          HomeListActivity localHomeListActivity4 = HomeListActivity.this;
          ListView localListView2 = HomeListActivity.this.mLvHome;
          List localList5 = HomeListActivity.this.mList;
          int i11 = paramInt;
          MBlog localMBlog2 = (MBlog)localList5.get(i11);
          HomeListActivity localHomeListActivity5 = HomeListActivity.this;
          int i12 = paramInt;
          boolean bool8 = localHomeListActivity5.isNewCommer(i12);
          int i13 = HomeListActivity.this.mReadMode;
          localObject2 = new MBlogListItemView(localHomeListActivity4,
 localListView2, localMBlog2, bool1, bool2, bool3, bool8, i13);
        }
      }
    }

代码说明：

代码流程已经比较混乱，但是这里能看到并没有直接的inflate，而是自定义了继承自LinearLayout的MBlogListItemView。

MBlogListItemView

public MBlogListItemView(Context paramContext, ListView paramListView,
 MBlog paramMBlog, boolean paramBoolean1, boolean paramBoolean2, 
boolean paramBoolean3, boolean paramBoolean4, int paramInt)
  {
    super(paramContext);
    this.context = paramContext;
    this.parent = paramListView;
    this.mBlog = paramMBlog;
    String str1 = paramContext.getCacheDir().getAbsolutePath();
    this.mCacheDir = str1;
    String str2 = paramContext.getFilesDir().getAbsolutePath();
    this.mFileDir = str2;
    ((LayoutInflater)paramContext.getSystemService("layout_inflater")).inflate(2130903061, this);
    TextView localTextView1 = (TextView)findViewById(2131624016);
    this.mName = localTextView1;
    TextView localTextView2 = (TextView)findViewById(2131624041);
    this.mDate = localTextView2;
    TextView localTextView3 = (TextView)findViewById(2131624018);
    this.mContent = localTextView3;
    TextView localTextView4 = (TextView)findViewById(2131624046);
    this.mSubContent = localTextView4;
    ImageView localImageView1 = (ImageView)findViewById(2131624040);
    this.mIconV = localImageView1;
    ImageView localImageView2 = (ImageView)findViewById(2131624042);
    this.mIconPic = localImageView2;
    ImageView localImageView3 = (ImageView)findViewById(2131624044);
    this.mUploadPic1 = localImageView3;
    ImageView localImageView4 = (ImageView)findViewById(2131623979);
    this.mUploadPic2 = localImageView4;
    TextView localTextView5 = (TextView)findViewById(2131624047);
    this.tvForm = localTextView5;
    TextView localTextView6 = (TextView)findViewById(2131623989);
    this.tvComment = localTextView6;
    this.tvComment.setOnClickListener(this);
    TextView localTextView7 = (TextView)findViewById(2131623988);
    this.tvRedirect = localTextView7;
    this.tvRedirect.setOnClickListener(this);
    ImageView localImageView5 = (ImageView)findViewById(2131624049);
    this.imComment = localImageView5;
    this.imComment.setOnClickListener(this);
    ImageView localImageView6 = (ImageView)findViewById(2131624048);
    this.imRedirect = localImageView6;
    this.imRedirect.setOnClickListener(this);
    ImageView localImageView7 = (ImageView)findViewById(2131624043);
    this.imGpsIcon = localImageView7;
    ImageView localImageView8 = (ImageView)findViewById(2131624013);
    this.mPortrait = localImageView8;
    LinearLayout localLinearLayout = (LinearLayout)findViewById(2131624045);
    this.mSubLayout = localLinearLayout;
    this.mReadMode = paramInt;
    MBlogListItemView localMBlogListItemView = this;
    MBlog localMBlog = paramMBlog;
    boolean bool1 = paramBoolean1;
    boolean bool2 = paramBoolean2;
    boolean bool3 = paramBoolean4;
    int i = paramInt;
    localMBlogListItemView.update(localMBlog, bool1, bool2, bool3, i);
    this.mUploadPic1.setOnClickListener(this);
    this.mUploadPic2.setOnClickListener(this);
  }

复制代码

代码说明：

a).MBlogListItemView extends LinearLayout implements MainListItemView

b).inflate(2130903061,this)这个数字代表R.layout.itemview。

二、测试方案（方案五）

按照新浪微博类似的做法进行测试。

2.1测试代码

@Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // 开始计时
            long startTime = System.nanoTime();

TestItemLayout item;
if (convertView == null) {
item = new TestItemLayout(BaseAdapterActivity.this);
} else
item = (TestItemLayout) convertView;
item.icon1.setImageResource(R.drawable.icon);
item.text1.setText(mData[position]);
item.icon2.setImageResource(R.drawable.icon);
item.text2.setText(mData[position]);

// 停止计时
long endTime = System.nanoTime();
// 计算耗时
long val = (endTime - startTime) / 1000L;
Log.e("Test", "Position:" + position + ":" + val);
if (count < 100) {
if (val < 2000L) {
sum += val;
count++;
}
} else
mTV.setText(String.valueOf(sum / 100L) + ":" + nullcount);// 显示统计结果
return item;
}

TestItemLayout

public class TestItemLayout extends LinearLayout {

public TextView text1;
public ImageView icon1;
public TextView text2;
public ImageView icon2;

public TestItemLayout(Context context) {
super(context);
((LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(
R.layout.list_item_icon_text, this);
icon1 = (ImageView) findViewById(R.id.icon1);
text1 = (TextView) findViewById(R.id.text1);
icon2 = (ImageView) findViewById(R.id.icon2);
text2 = (TextView) findViewById(R.id.text2);
}
}

2.2测试结果

三、总结

从测试结果来看与ViewHolder性能非常接近，不会出现tag图片变小的问题(关于图片变小的问题，有朋友说是TAG中的元素对大小和位置有记忆)，也能有效的减少findViewById的执行次数，这里建议完全可以取代ViewHolder。

2312 次浏览