Android layout Inflate 性能浅析
16lz
2021-01-23
Android layout Inflate 性能浅析
本文从三个测试方法测试 android 的 LayoutInflater.inflate 函数的性能。先上代码;
以下的时间的单位都是ns（纳秒）
package com.chillingvan.samplecode.xml;import android.app.Activity;import android.content.res.XmlResourceParser;import android.os.Bundle;import android.util.Log;import android.view.LayoutInflater;import android.widget.Toast;import com.chillingvan.samplecode.R;public class XmlActivity extends Activity { private static final String TAG = "XmlActivity"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_xml); testInflatePerformance(); testInflateWithXmlParserPerformance(); testFindViewTime(); } private void testInflatePerformance() { long initTime = System.nanoTime(); int times = 50; for (int i = 0; i < times; i++) { long eachInitTime = System.nanoTime(); LayoutInflater.from(this).inflate(R.layout.activity_xml, null); Log.d(TAG, "each parser time cost=" + (System.nanoTime() - eachInitTime )); } long timeCost = System.nanoTime() - initTime; String log = String.format("testInflatePerformance: %d times time cost=%d ns", times, timeCost); Log.d(TAG, log); Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show(); } private void testInflateWithXmlParserPerformance() { long initTime = System.nanoTime(); // can only be setted to 1 because the parser cannot be reused. // But the parser creating does not cost time.. // Because the parse time is the main part of the cost. int times = 1; XmlResourceParser xmlResourceParser = getResources().getLayout(R.layout.activity_xml); for (int i = 0; i < times; i++) { long eachInitTime = System.nanoTime(); LayoutInflater.from(this).inflate(xmlResourceParser, null); Log.d(TAG, String.format("each parser time cost=%d ns",(System.nanoTime() - eachInitTime ))); } long timeCost = System.nanoTime() - initTime; String log = String.format("testInflateWithXmlParserPerformance: %d times time cost=%d ns", times, timeCost); Log.d(TAG, log); Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show(); } private void testFindViewTime() { long initTime = System.nanoTime(); int times = 40; for (int i = 0; i < times; i++) { long eachInitTime = System.nanoTime(); findViewById(R.id.xml_txt); Log.d(TAG, String.format("each parser time cost=%d ns",(System.nanoTime() - eachInitTime ))); } long timeCost = System.nanoTime() - initTime; String log = String.format("testFindViewTime: %d times time cost=%d ns", times, timeCost); Log.d(TAG, log); Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show(); }}来看第一个inflate(int res, ViewGroup)方法的测试性能：
private void testInflatePerformance() { long initTime = System.nanoTime(); int times = 50; for (int i = 0; i < times; i++) { long eachInitTime = System.nanoTime(); LayoutInflater.from(this).inflate(R.layout.activity_xml, null); Log.d(TAG, "each parser time cost=" + (System.nanoTime() - eachInitTime )); } long timeCost = System.nanoTime() - initTime; String log = String.format("testInflatePerformance: %d times time cost=%d ns", times, timeCost); Log.d(TAG, log); Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show(); }连续inflate同一个layout文件50次的结果如下：
可以看到每次inflate所花费的时间大致相同，说明 android 不会对重复 inflate 的数据进行缓存。
第二个方法：
private void testInflateWithXmlParserPerformance() { long initTime = System.nanoTime(); // can only be setted to 1 because the parser cannot be reused. // But the parser creating does not cost time.. // Because the parse time is the main part of the cost. int times = 1; XmlResourceParser xmlResourceParser = getResources().getLayout(R.layout.activity_xml); for (int i = 0; i < times; i++) { long eachInitTime = System.nanoTime(); LayoutInflater.from(this).inflate(xmlResourceParser, null); Log.d(TAG, String.format("each find view time cost=%d ns",(System.nanoTime() - eachInitTime ))); } long timeCost = System.nanoTime() - initTime; String log = String.format("testInflateWithXmlParserPerformance: %d times time cost=%d ns", times, timeCost); Log.d(TAG, log); Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show(); }inflate((XmlPullParser parser, ViewGroup root))这个方法传给inflate的参数是一个 XmlResourceParser。 原本是用来测试性能的，但是实际上测不了，因为获取到的parser只能用来解析一次，再调用一次就会报错。
inflate((XmlPullParser parser, ViewGroup root))其实是inflate (int resource, ViewGroup root)内部使用的方法，可以在源码上找到相应细节。
结果：
可以看到和第一个方法差别不大，也就是说Inflate的消耗时间注意不是由获取parser这一过程消耗的。
第三个方法：
private void testFindViewTime() {
long initTime = System.nanoTime();
int times = 40;
for (int i = 0; i < times; i++) {
long eachInitTime = System.nanoTime();
findViewById(R.id.xml_txt);
Log.d(TAG, String.format("each parser time cost=%d ns",(System.nanoTime() - eachInitTime )));
}
long timeCost = System.nanoTime() - initTime;
String log = String.format("testFindViewTime: %d times time cost=%d ns", times, timeCost);
Log.d(TAG, log);
Toast.makeText(XmlActivity.this, log, Toast.LENGTH_SHORT).show();
}
结果：
这个是测试findView的性能，从结果可以看到findView耗费的时间不多。
那么inflate方法花费的时间主要花在哪一部分？
/** * Recursive method used to descend down the xml hierarchy and instantiate * views, instantiate their children, and then call onFinishInflate(). * * @param inheritContext Whether the root view should be inflated in its * parent's context. This should be true when called inflating * child views recursively, or false otherwise. */ void rInflate(XmlPullParser parser, View parent, final AttributeSet attrs, boolean finishInflate, boolean inheritContext) throws XmlPullParserException, IOException { final int depth = parser.getDepth(); int type; while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) { if (type != XmlPullParser.START_TAG) { continue; } final String name = parser.getName(); if (TAG_REQUEST_FOCUS.equals(name)) { parseRequestFocus(parser, parent); } else if (TAG_TAG.equals(name)) { parseViewTag(parser, parent, attrs); } else if (TAG_INCLUDE.equals(name)) { if (parser.getDepth() == 0) { throw new InflateException("猜测主要花费在rInflate方法这里，是一个递归方法。
最后，总结以下，inflate方法的性能瓶颈不在读磁盘，而在解析上，所以越view 层级复杂的layout越低性能。
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