Android 使用LayoutInflater.Factory2建立布局
一,解析LayoutInflater运行原理
从建立一个LayoutInflater的方式咱们能够知道，LayoutInflater是系统提供的单例对象android
LayoutInflater layoutInflater = getLayoutInflater(); ↓ LayoutInflater layoutInflater = LayoutInflater.from(context); ↓ LayoutInflater LayoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
boolean equals = getLayoutInflater().equals(LayoutInflater.from(this));
Log.e("equals", "value="+equals);
#输出value=true #说明LayoutInflater具备全局属性
关于Inflate方法,主要分为2组，但前2组最终也是经过调用后2组中的某一个方法来实现的缓存
inflate(int resource, ViewGroup root) inflate(int resource, ViewGroup root, boolean attachToRoot) ------------------------------------------------------------------------- inflate(XmlPullParser parser, ViewGroup root) inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)
inflate方法最终会调用以下方法，固然这是必然的，由于咱们须要解析这个布局文件app
inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)
关于XmlPullParser parser解析器的获取，Android内部采用了XmlpullParser解析xml，这种解析相似与SAX Parser技术，效率高，由于它以IO流的方式进行解析和读取ide
咱们来看一下XmlPullParser获取的这个实现方式布局
public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
if (DEBUG) System.out.println("INFLATING from resource: " + resource);
XmlResourceParser parser = getContext().getResources().getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
在Android内部XmlResourceParser继承自XmlPullParserthis
public interface XmlResourceParser extends XmlPullParser, AttributeSet {
/**
* Close this interface to the resource. Calls on the interface are no
* longer value after this call.
*/
public void close();
}
实际咱们经过Resource获取到的是XmlResourceParserspa
XmlResourceParser xml = getResources().getXml(R.xml.gateway); XmlResourceParser layout = getResources().getLayout(R.layout.fragment_main);
这里注意，其实获取资源的时候，都会经过XmlResourceParser，只是内部进行了必要的封装而已，有兴趣的 猿猿同窗 能够查看Resource的实现代码code
再来看看inflate的实现xml
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context)mConstructorArgs[0];
mConstructorArgs[0] = mContext;
View result = root;
try {
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
//从文档头文档开始解析，这里忽略文档头
}
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
if (TAG_MERGE.equals(name)) {
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
rInflate(parser, root, attrs, false);
} else {
// Temp is the root view that was found in the xml
View temp;
if (TAG_1995.equals(name)) {
temp = new BlinkLayout(mContext, attrs);
} else {
temp = createViewFromTag(root, name, attrs);
}
ViewGroup.LayoutParams params = null;
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
if (DEBUG) {
System.out.println("-----> start inflating children");
}
// Inflate all children under temp
rInflate(parser, temp, attrs, true);
if (DEBUG) {
System.out.println("-----> done inflating children");
}
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
root.addView(temp, params);
}
// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
result = temp;
}
}
} catch (XmlPullParserException e) {
InflateException ex = new InflateException(e.getMessage());
ex.initCause(e);
throw ex;
} catch (IOException e) {
InflateException ex = new InflateException(
parser.getPositionDescription()
+ ": " + e.getMessage());
ex.initCause(e);
throw ex;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
return result;
}
}
基本上就是解析xml的过程，xml解析原本过慢，所以在开发中应该减小使用inflate，采用ViewHolder和SparseArray缓存View是一个不错的选择对象
对于属性的读取，咱们看到
XmlResourceParser parser = getResources().getLayout(resid); final AttributeSet attrs = Xml.asAttributeSet(parser);
咱们看到，使用了android.util.Xml类
public static AttributeSet asAttributeSet(XmlPullParser parser) {
return (parser instanceof AttributeSet)
? (AttributeSet) parser
: new XmlPullAttributes(parser);
}
AttributeSet 会最终被返回给View的Context
二.使用LayoutInflater.Factory2控件工厂
Android自定义控件的思想，获取自定义属性通常会在构造方法中，经过TypeArray和obtainStyledAttributes(resid, attrs)方法，但obtainStyledAttributes(resid, attrs)是没有公开的方法，对于这一点要特别之处，在外部没法得到自定属性，除非从新使用XmlPullParser解析，从而获得相应的数据值。
特别是对于Android MVVM开发而言，如何访问绑定字段，对于这一问而言，咱们须要构建本身的LayoutInflater或者经过XmlPullParser解析以后与对应的view自动匹配，不事后者简单，但效率会有所损失。
综上，obtainStyledAttributes(resid, attrs)具备局限性，咱们能够利用LayoutInflater.Factory2来实现属性的获取和View的重建。
先看看LayoutInflater类中的createViewFromTag源码：
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}
if (name.equals(TAG_1995)) {
return new BlinkLayout(context, attrs); //内部Layout，不用理会
}
try {
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs); //在这里调用了Factory2的接口
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);//在这里调用了Factory的接口，Factory2也继承了Factory
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs); //私有实现的Factory2
}
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
} catch (InflateException e) {
throw e;
} catch (ClassNotFoundException e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;
}
}
咱们实现Factory2工厂便可，返回值能够为null,也能够自行实现建立View，咱们这里选择实现建立View
public class ViewCreateFactory implements Factory2 ,LayoutInflater.Filter{
private static ViewCreateFactory instance;
private Context mContext;
private OnInflaterListener onInflaterlistener;
private LayoutInflater mInflater;
private LayoutInflater.Filter mFilter;
private final static String DEFAULT_VIEW_PREFIX = "android.view.";
private final static String DEFAULT_WIDGET_PREFIX = "android.widget.";
public void setOnInflaterListener(OnInflaterListener listener) {
this.onInflaterlistener = listener;
}
public static ViewCreateFactory create(Context ctx,LayoutInflater inflater) //在onCreate中调用
{
if(instance ==null)
{
synchronized (ViewCreateFactory.class)
{
if(instance ==null)
{
instance = new ViewCreateFactory(ctx);
}
}
}
instance.setOnInflaterListener(null);
instance.setFilter(null);
instance.setLayoutInflater(inflater);
return instance;
}
public void setLayoutInflater(LayoutInflater inflater) {
this.mInflater = inflater;
this.mInflater.setFactory2(this); //建工厂设置到LayoutInflater中
this.mFilter = this.mInflater.getFilter();
this.mInflater.setFilter(this);
}
private ViewCreateFactory(Context context)
{
this.mContext = context;
}
public void setFilter(LayoutInflater.Filter filter) {
this.mFilter = filter;
}
@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
return onCreateView(name, context, attrs);
}
@Override
public View onCreateView(String name, Context context, AttributeSet attrs) {
try{
View view = null;
if (-1 == name.indexOf('.'))
{
Class<?> clazz = ReflectUtils.loadClass(mContext, DEFAULT_VIEW_PREFIX.concat(name));
if(clazz!=null)
{
view = mInflater.createView(name, DEFAULT_VIEW_PREFIX, attrs); //这里咱们调用LayoutInflater建立View的方法，固然也能够自定义
}
else
{
view = mInflater.createView(name,DEFAULT_WIDGET_PREFIX, attrs);
}
} else {
view = mInflater.createView(name, null, attrs);
}
if(onInflaterlistener !=null)
{
onInflaterlistener.onCreateView(view,attrs);
}
return view;
}
catch (Exception e)
{
Log.e("InflaterERROR",e.getLocalizedMessage());
e.printStackTrace();
}
return null;
}
@Override
public boolean onLoadClass(Class clazz)
{
onInflaterlistener.onLoadClass(clazz);
if(this.mFilter!=null)
{
return mFilter.onLoadClass(clazz);
}
return true;
}
//在onDestory中调用,由于LayoutInflater是全局的，所以，为了让Activity回收正常，结束时必须调用此方法
public void release()
{
this.mInflater.setFactory2(null);
this.mInflater.setFilter(null);
this.mInflater = null;
}
public interface OnInflaterListener
{
//用于向外部提供属性和View，咱们能够从类外部获取到属性了
public void onCreateView(view,attrs);
}
}
//这里咱们调用LayoutInflater建立View的方法，固然也能够自定义实现本身建立方法 view = mInflater.createView(name, prefix, attrs);
public interface OnInflaterListener
{
//用于向外部提供属性和View，咱们能够从类外部获取到属性了
public void onCreateView(View view,AttributeSet attrs);
}
使用方式
LayoutInflater inflater = LayoutInflater.from(context);
ViewCreateFactory factory = ViewCreateFactory.create(context,inflater);
factory.setOnInflaterListener(new ViewCreateFactory.OnInflaterListener{
public void onCreateView(View view,AttributeSet attrs)
{
//从这里获取attrs,里面包含自定义属性
}
});
三.LayoutInflater可替代方式
TextView myView = (TextView)View.inflate(context, resource, root);
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