LayoutInflater中inflate過程全解析
LayoutInflater類中的inflate方法是咱們經常使用的一個工具,無論是自定義view仍是ListView這類adapter類中，inflate方法都能幫助咱們生成咱們須要的view。那麼inflate的原理是什麼呢？下面就來分析下源碼。java
inflate方法有幾個重載的方法，可是最後都是調用到了其中的一個方法，也就是View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) ，那麼咱們就從這個方法開始往下看。node
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
//1. 保留上一次的context對象
Context lastContext = (Context) mConstructorArgs[0];
//2.存儲當前inflate的context對象
mConstructorArgs[0] = inflaterContext;
View result = root;
try {
// Look for the root node.
int type;
//3.找到第一個START_TAG
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
final String name = parser.getName();
...
//4.處理merge標籤
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, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
//5.建立xml中的view對象
final View temp = createViewFromTag(root, name, inflaterContext, 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
//6.獲取root中默認的layoutParams
params = root.generateLayoutParams(attrs);
//7.若是不須要add到root中
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
...
// Inflate all children under temp against its context.
//8.處理其餘的子view
rInflateChildren(parser, temp, attrs, true);
...
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
//9.addview到rootview中去
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 (Exception 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;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}
在代碼1處，用到了一個成員變量mConstructorArgs，這是一個大小爲2的數組，用來存儲view構造中須要用到兩個對象：context和attributeSet.在代碼3處，經過一個while循環處理，找到xml中的第一個start_tag,也就是咱們定義的root view。在代碼4處，這裏主要用來處理xml定義的<merge>標籤，這裏不做贅述。在代碼5處，經過createViewFromTag方法建立了view，也就是咱們剛剛處理的start_tag中的view，因此真正的建立是在這個方法中，咱們來看下這個方法。android
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
//1.處理view標籤
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
// Apply a theme wrapper, if allowed and one is specified.
//2.若是指定了Theme屬性，用ContextThemeWrapper包裝一下
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();
}
//3.處理blink標籤
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}
try {
//4.mFactory，mFactory2提供了一種便捷操做讓咱們能夠本身定製view
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}
if (view == null) {
//5.若是沒有指定上面的factory信息，那麼久調用下面的機制建立view
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
//6.系統view
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
//7.自定義的view
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;
}
}
代碼1處，用來處理咱們在xml中定義的<view class="">標籤，獲取view的類名。在代碼2處，若是xml中有定義theme，須要用定義的Theme來wrapper一下context,生成一個新的ContextThemeWrapper。代碼3處用來處理<Blink>標籤，它是一種閃爍的佈局處理，不細究。在代碼4處，有多個Factory，這個幾個Factory的做用是LayoutInflater爲咱們提供了一些工廠方法，讓咱們本身去createView，默認都是沒有這些Factory方法。從代碼5處開始就是LayoutInflate的內部建立view的過程。首先保存一下context，而後判斷咱們的view的name中是否有.,也就是判斷是不是自定義的view仍是系統中的view，咱們只看系統view的建立方法，也就是從代碼6處開始往下看，調用onCreateView方法.數組
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 {
//1.檢查map緩存中是否有緩存的構造器
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
//2.獲取name表示的Class對象
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
//3.filter過濾class對象
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
}
//4.獲取構造器
constructor = clazz.getConstructor(mConstructorSignature);
constructor.setAccessible(true);
//5.緩存構造器
sConstructorMap.put(name, constructor);
} else {
// If we have a filter, apply it to cached constructor
if (mFilter != null) {
// Have we seen this name before?
Boolean allowedState = mFilterMap.get(name);
if (allowedState == null) {
// New class -- remember whether it is allowed
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, attrs);
}
}
}
//6.args實參，第一個參數是context
Object[] args = mConstructorArgs;
args[1] = attrs;
//7.反射獲取view，調用的就是new View(Context,AttributeSet)
final View view = constructor.newInstance(args);
if (view instanceof ViewStub) {
// Use the same context when inflating ViewStub later.
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
return view;
} catch (NoSuchMethodException e) {
InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class "
+ (prefix != null ? (prefix + name) : name));
ie.initCause(e);
throw ie;
}
...
}
代碼1處檢查sConstructorMap中是否有當前view的緩存的構造器，第一次處理的時候都沒有，往下繼續看。代碼2處，使用反射，直接獲得了一個view的Class對象，而後使用mFilter檢查這個class對象是不是咱們容許建立的Class對象，默認這個filter是不做過濾的。代碼4處，經過這個class對象建立一個Constructor構造器對象，從mConstructorSignature這個對象上能夠看出，使用的是public View(Context, AttributeSet)這個構造器。代碼5處用來緩存這個構造器對象。代碼6處用來傳參，第一個參數是context已經在以前的方法中設置過，args[1]傳遞attributeSet對象。代碼7處使用反射直接生成了View,這樣最後就生成了咱們須要View對象了。緩存
回到inflate方法中，createViewFromTag已經建立了咱們指定的view，接着往下看。代碼六、7中，若是提供了inflate方法中第二個參數ViewGroup的話，會獲取這個ViewGroup中的layoutParams,而且將它設置給剛剛生成出來的View上。處理完這些以後也就是晶晶處理了最開始的rootView，其餘的子節點的view尚未處理。因此在代碼8處，就是處理接下來的子view。咱們大體看一下代碼.app
final void rInflateChildren(XmlPullParser parser, View parent, AttributeSet attrs,
boolean finishInflate) throws XmlPullParserException, IOException {
rInflate(parser, parent, parent.getContext(), attrs, finishInflate);
}
void rInflate(XmlPullParser parser, View parent, Context context,
AttributeSet attrs, boolean finishInflate) 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("<include /> cannot be the root element");
}
parseInclude(parser, context, parent, attrs);
} else if (TAG_MERGE.equals(name)) {
throw new InflateException("<merge /> must be the root element");
} else {
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
rInflateChildren(parser, view, attrs, true);
viewGroup.addView(view, params);
}
}
if (finishInflate) {
parent.onFinishInflate();
}
}
大體看一下，仍是同樣的配方，使用createViewFromTag建立接下來的每一個子View，因此不細究了。ide
最後在inflate方法中還須要判斷是否須要將當前建立的view 加到第二個參數提供的ViewGroup中，這個判斷就是第三個參數提供的。大體的流程也就是這樣吧~~工具
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