Android中级——getSystemService和LayoutInflater
getSystemService和LayoutInflater
- 使用容器管理单例模式
- getSystemService()
- LayoutInflater
使用容器管理单例模式
将单例统一管理，隐藏实现，第一次获取时创建，下次直接从缓存中获取，避免重复创建对象
class SingletonManager {
private static Map sMap = new HashMap<>();
private SingletonManager() {
}
public static void registerService(String key, Object instance) {
if (!sMap.containsKey(key)) {
sMap.put(key, instance);
}
}
public static Object getService(String key) {
return sMap.get(key);
}
}
getSystemService()
上述代码其实就是Context中getSystemService()获取系统服务的简略实现，其是抽象方法，实现类是ContextImpl，如下
@Override
public Object getSystemService(String name) {
......
return SystemServiceRegistry.getSystemService(this, name);
}
调用SystemServiceRegistry的getSystemService()，如下
public static Object getSystemService(ContextImpl ctx, String name) {
if (name == null) {
return null;
}
final ServiceFetcher fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
if (fetcher == null) {
......
return null;
}
final Object ret = fetcher.getService(ctx);
......
return ret;
}
SYSTEM_SERVICE_FETCHERS存储ServiceFetcher，其在static语句块进行注册，如下
private static final Map> SYSTEM_SERVICE_FETCHERS = new ArrayMap>();
private static void registerService(String serviceName, Class serviceClass, ServiceFetcher serviceFetcher) {
......
SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}
static {
......
registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
new CachedServiceFetcher() {
@Override
public LayoutInflater createService(ContextImpl ctx) {
return new PhoneLayoutInflater(ctx.getOuterContext());
}});
......
}
会调用ServiceFetcher的子类的CachedServiceFetcher的getService()，若已经创建则从缓存中获取，否则调用createService()创建并加入缓存
static abstract interface ServiceFetcher {
T getService(ContextImpl ctx);
}
static abstract class CachedServiceFetcher implements ServiceFetcher {
......
@Override
@SuppressWarnings("unchecked")
public final T getService(ContextImpl ctx) {
final Object[] cache = ctx.mServiceCache;
......
T ret = null;
for (;;) {
......
synchronized (cache) {
T service = (T) cache[mCacheIndex];
if (service != null || ......) {
ret = service;
break;
}
......
}
if (doInitialize) {
T service = null;
......
try {
service = createService(ctx);
......
}......
ret = service;
break;
}
......
}
.....
return ret;
}
public abstract T createService(ContextImpl ctx) throws ServiceNotFoundException;
}
LayoutInflater
LayoutInflater是抽象类，分析其inflate()方法，如果有预先编译则设置LayoutParams返回View
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
......
View view = tryInflatePrecompiled(resource, res, root, attachToRoot);
if (view != null) {
return view;
}
XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
否则通过xml解析器解析
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
View result = root;
try {
advanceToRootNode(parser);
final String name = parser.getName(); //找到第一个标签元素
......
if (TAG_MERGE.equals(name)) { //加载merge标签，并依附到root
......
rInflate(parser, root, inflaterContext, attrs, false);
} else {
//解析非merge标签，name即为控件名如LinearLayout
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
ViewGroup.LayoutParams params = null;
if (root != null) {
......
params = root.generateLayoutParams(attrs); //若root不为空根据root生成LayoutParams
if (!attachToRoot) { //若不依附到root则直接为View设置LayoutParams
temp.setLayoutParams(params);
}
}
......
rInflateChildren(parser, temp, attrs, true); //解析子View并依附到temp
......
if (root != null && attachToRoot) { //若依附到root则添加
root.addView(temp, params);
}
......
if (root == null || !attachToRoot) { //若不依附到root则直接返回
result = temp;
}
}
}......
return result;
}
}
调用createViewFromTag()生成View的过程如下
private View createViewFromTag(View parent, String name, Context context, AttributeSet attrs) {
return createViewFromTag(parent, name, context, attrs, false);
}
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
if (!ignoreThemeAttr) { //加载自定义的attr标签
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();
}
try {
View view = tryCreateView(parent, name, context, attrs); //使用自定义的LayoutInflater.Factory加载View
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) { //若不存在.说明是系统控件，调用onCreateView()加上包名
view = onCreateView(context, parent, name, attrs);
} else { //自定义控件自带包名com.xxx.xxx
view = createView(context, name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
}......
}
@Nullable
public View onCreateView(@NonNull Context viewContext, @Nullable View parent,
@NonNull String name, @Nullable AttributeSet attrs)
throws ClassNotFoundException {
return onCreateView(parent, name, attrs);
}
protected View onCreateView(View parent, String name, AttributeSet attrs)
throws ClassNotFoundException {
return onCreateView(name, attrs);
}
接下来会调用到子类PhoneLayoutInflater的onCreateView()，为系统控件添加上包名
public class PhoneLayoutInflater extends LayoutInflater {
private static final String[] sClassPrefixList = {
"android.widget.",
"android.webkit.",
"android.app."
};
@Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
for (String prefix : sClassPrefixList) {
try {
View view = createView(name, prefix, attrs);
if (view != null) {
return view;
}
}......
}
return super.onCreateView(name, attrs);
}
}
再调用回LayoutInflater的onCreateView()、createView()
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Context context = (Context) mConstructorArgs[0];
if (context == null) {
context = mContext;
}
return createView(context, name, prefix, attrs);
}
最终和自定义View一样调用到4个参数的createView()
public final View createView(@NonNull Context viewContext, @NonNull String name, @Nullable String prefix, @Nullable AttributeSet attrs) throws ClassNotFoundException, InflateException {
......
//从缓存中获取构造函数，若不是同一个ClassLoader则置空和删除缓存
Constructor constructor = sConstructorMap.get(name);
if (constructor != null && !verifyClassLoader(constructor)) {
constructor = null;
sConstructorMap.remove(name);
}
Class clazz = null;
try {
......
if (constructor == null) { //若构造函数不在缓存，则根据包名生成构造函数添加到缓存
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
constructor = clazz.getConstructor(mConstructorSignature);
constructor.setAccessible(true);
sConstructorMap.put(name, constructor);
}......
Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = viewContext;
Object[] args = mConstructorArgs;
args[1] = attrs;
try {
final View view = constructor.newInstance(args); //利用反射构造View
if (view instanceof ViewStub) {
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
return view;
}......
}......
}
接下来分析用于解析View树的rInflateChildren()
final void rInflateChildren(XmlPullParser parser, View parent, AttributeSet attrs,
boolean finishInflate) throws XmlPullParserException, IOException {
rInflate(parser, parent, parent.getContext(), attrs, finishInflate);
}
调用rInflate()
void rInflate(XmlPullParser parser, View parent, Context context, AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
final int depth = parser.getDepth(); //深度优先遍历获取树的深度
int type;
boolean pendingRequestFocus = false;
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)) { //解析requestFocus标签
pendingRequestFocus = true;
consumeChildElements(parser);
} else if (TAG_TAG.equals(name)) { //解析tag标签
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) { //解析include标签
if (parser.getDepth() == 0) {
throw new InflateException("