在看了一些vogella的文章之后，发现关于android listview性能优化这一段很有意思，于是实践了一下，经过优化，性能确实提升不少！
先看看优化前和优化后的比较：
优化前的log截图:
优化后的log截图：
并且，在不停滚动ListView的过程中，优化之前会出现ANR现象，在AVD上特别容易复现：
然后，优化后显得很流畅，附上对于的log截图：
下面附上相关代码分析：
ListView中的每一个Item由一个ImageView 和一个TextView组成
Layout:
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<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="horizontal" > <ImageView android:id="@+id/imageView" android:layout_width="wrap_content" android:layout_height="fill_parent" />" <TextView android:id="@+id/textView" android:layout_width="wrap_content" android:layout_height="fill_parent" android:layout_marginLeft="15dp" android:gravity="center_vertical" /> </LinearLayout>
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Activity继承自ListActivity，我故意增加了Item，方便测试，效果更明显：
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public class ListViewDemo extends ListActivity{ private final String[] mItems = new String[] { "Android", "iPhone", "WindowsMobile", "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2" }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ListViewArrayAdapter adapter = new ListViewArrayAdapter(this, mItems); getListView().setAdapter(adapter); } }
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然后custom Adapter，优化之前的adapter:
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@Override public View getView(int position, View convertView, ViewGroup parent) { long start = System.currentTimeMillis(); LayoutInflater inflater = (LayoutInflater) mContext.getLayoutInflater(); View rowView = inflater.inflate(mViewResourceId, parent, false); TextView textView = (TextView) rowView .findViewById(mTextViewResourceId); ImageView imageView = (ImageView) rowView .findViewById(mImageViewResourceId); textView.setText(mNames[position]); String s = mNames[position]; if (s.startsWith("Windows7") || s.startsWith("iPhone")) { imageView.setImageResource(R.drawable.no); } else { imageView.setImageResource(R.drawable.yes); } Log.v("jerikc","cost time = " + (System.currentTimeMillis() - start)); return rowView; }
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优化之后的Adapter：
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public class ListViewArrayAdapter extends ArrayAdapter<String>{ private final Activity mContext; private final String[] mNames; private final static int mViewResourceId = R.layout.text_image_row_layout; private final static int mTextViewResourceId = R.id.textView; private final static int mImageViewResourceId = R.id.imageView; static class ViewHolder { public TextView text; public ImageView image; } public ListViewArrayAdapter(Activity context, String[] names) { super(context, mViewResourceId, names); this.mContext = context; this.mNames = names; } @Override public View getView(int position, View convertView, ViewGroup parent) { long start = System.currentTimeMillis(); View rowView = convertView; if (rowView == null) { LayoutInflater inflater = mContext.getLayoutInflater(); rowView = inflater.inflate(mViewResourceId, null); ViewHolder viewHolder = new ViewHolder(); viewHolder.text = (TextView) rowView.findViewById(mTextViewResourceId); viewHolder.image = (ImageView) rowView.findViewById(mImageViewResourceId); rowView.setTag(viewHolder); } ViewHolder holder = (ViewHolder) rowView.getTag(); String s = mNames[position]; holder.text.setText(s); if (s.startsWith("Windows7") || s.startsWith("iPhone")) { holder.image.setImageResource(R.drawable.no); } else { holder.image.setImageResource(R.drawable.yes); } Log.v("jerikc","cost time = " + (System.currentTimeMillis() - start)); return rowView; } }
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优化的大致思想就是：优化之前，每次加载item的时候，都要加载一下布局文件，然后生成一个新的row View对象，然后通过View找到对应的ImageView和TextView，正如我们所知道的那样，加载布局文件时很耗时的，特别是在操作比较频繁 情况下，这是不可忍受的，所以会导致ANR现象。
因此，我们可以重复利用已不可见的row View对象。Android中，当它决定让row View对象不可见的时候，它允许通过getView方法中的convertView参数来重复利用刚刚不可见的row View对象。
在优化的过程中，第一次加载的时候，我们需要把相关的数据保存起来，而View有一个方法setTag，该方法可用来保存一些数据结构。我们一个row View对象是由ImageView和TextView空间组成的，因此定义一个ViewHolder来保存ImageView和TextView对象。 在重复利用的过程中，只需简单修改它们的值，而不用再次findViewById。