源碼分析-setContentView都做了些什么
一直以來(lái)只是盲目的寫(xiě)代碼,然后教程上入門(mén)時(shí)候也是告訴你這么做就OK了,有很多東西都不知道為什么,最近正好搞了份6.0的源碼,所以就試著來(lái)分析下之前感覺(jué)迷茫的點(diǎn),本次要探究我們?cè)贏ctivity的Oncreate方法里面調(diào)用setContentView都做了些什么
- 開(kāi)始之前先說(shuō)下本次用到的工具以及源碼獲取方式,本次主要用到的工具Source Insight
- 源碼獲取方式:
1、自己搞個(gè)Linux虛擬機(jī)然后下載,這個(gè)自己可以去搜索相關(guān)教程
2、福利(需要翻墻),當(dāng)然我下載了是Android6.0的FrameWork層的代碼,如果你要燒錄的話,請(qǐng)參考1
Activity
Activity.java的位置framework\base\core\java\android\app
這里左邊欄搜索setContentView方法可以看到有三個(gè)重載的方法,如下圖
1496208214112.png
這個(gè)三個(gè)方法的代碼結(jié)構(gòu)是這樣子的,相對(duì)源碼略有修改
public void setContentView(params params...) {
//調(diào)用Window的方法
getWindow().setContentView(params);
//初始化ActionBar
initWindowDecorActionBar();
}
PhoneWindow
追查發(fā)現(xiàn)Activity內(nèi)部持有的是一個(gè)private Window mWindow;所以我們接下來(lái)要搜索這個(gè)Window(位置framework\base\core\java\android\view)追查進(jìn)去發(fā)現(xiàn)這個(gè)Window是個(gè)抽象類(lèi),那么我們久要找他的實(shí)現(xiàn)類(lèi)PhoneWindow,接下來(lái)我們就可以查看這個(gè)PhoneWindow的setContentView的方法
public void setContentView(int layoutResID) {
...
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
...
} else {
//這里填充布局
mLayoutInflater.inflate(layoutResID, mContentParent);
}
...
}
mContentParent
這里可以查看mContentParent的聲明
// This is the view in which the window contents are placed. It is either
// mDecor itself, or a child of mDecor where the contents go.
private ViewGroup mContentParent;
意思大概是這個(gè)ViewGroup就是頂層的Decor或者他包含的要加載的子View(英文比較爛,英文好的童鞋可以自行理解)
LayoutInflater
這段代碼做了一些列的判斷然后調(diào)用了LayoutInflater的inflate方法,繼續(xù)追查L(zhǎng)ayoutInflater.java位于 framework\base\core\java\android\view目錄下,查看inflate方法
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
//首先獲取Xml布局中書(shū)寫(xiě)的資源
final XmlResourceParser parser = res.getLayout(resource);
try {
//這里做了填充
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
上面這段代碼可以看到主要是兩個(gè)方法
- res.getlayout用于獲取我們?cè)趚ml中聲明的標(biāo)簽
-
inflate(parser,root,attchToRoot)用于填充布局
首先我們先看res.getLayout(resource)這個(gè)方法主要用于加載清單文件中的一系列標(biāo)簽體,有興趣可以另行查看,inflate的代碼如下，一下代碼我盡量保留英文注釋方便英文水平比較好的同學(xué)查看
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
...
View result = root;
try {
// Look for the root node.找尋根節(jié)點(diǎn)
...
final String name = parser.；();
...
if (TAG_MERGE.equals(name)) {
//如果是merge標(biāo)簽走這里
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
//temp就是xml文件中的根節(jié)點(diǎn)
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
ViewGroup.LayoutParams params = null;
if (root != null) {
// Create layout params that match root, if supplied
//找到根節(jié)點(diǎn)的layoutparams
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
//講layoutparams交給根節(jié)點(diǎn)的View
temp.setLayoutParams(params);
}
}
// Inflate all children under temp against its context.
//遍歷跟節(jié)點(diǎn)temp所包涵的子View添加到temp中
rInflateChildren(parser, temp, attrs, true);
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
// root不為空，直接將根節(jié)點(diǎn)View添加到root中
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.
// root等于null,直接返回根節(jié)點(diǎn)temp
if (root == null || !attachToRoot) {
result = temp;
}
}
} catch (Exception e) {
...
} finally {
// Don't retain static reference on context.
//釋放資源
...
}
return result;
}
}
上面這段代碼主要有兩個(gè)方法需要注意
- rInflateChildren(parser, temp, attrs, true)
-
createViewFromTag(root, name, inflaterContext, attrs)
先看createViewFromTag的代碼
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) {
...
try {
View view;
...
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
return view;
}catch (Exception e) {
...
}
}
LayoutInflater#createView()
protected View onCreateView(View parent, String name, AttributeSet attrs)
throws ClassNotFoundException {
return onCreateView(name, attrs);
}
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
private static final HashMap<String, Constructor<? extends View>> sConstructorMap =
new HashMap<String, Constructor<? extends View>>();
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
//緩存過(guò)的View的構(gòu)造方法
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
//如果沒(méi)有緩存該View的構(gòu)造方法
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
...
constructor = clazz.getConstructor(mConstructorSignature);
constructor.setAccessible(true);
sConstructorMap.put(name, constructor);
} else {
// If we have a filter, apply it to cached constructor
//如果有緩存的構(gòu)造方法那就使用緩存的
...
}
//實(shí)例化出View
final View view = constructor.newInstance(args);
//ViewStub的懶加載...
...
return view;
}catch (Exception e) {
...
}
}
上面可以看到無(wú)論走那個(gè)分支最終都是會(huì)執(zhí)行createView的,那么這里面用一個(gè)HashMap來(lái)存儲(chǔ)已經(jīng)解析過(guò)的View,如果沒(méi)有解析過(guò)這個(gè)View,那么就直接反射獲取該View的構(gòu)造方法new出來(lái)一個(gè)實(shí)例,這里也可以看出為什么要避免頻繁的inflate操作
LayoutInflater#rInflateChildren
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 {
//獲取節(jié)點(diǎn)的深度
final int depth = parser.getDepth();
int type;
//循環(huán)遍歷節(jié)點(diǎn)
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
//跟標(biāo)簽跳過(guò)
if (type != XmlPullParser.START_TAG) {
continue;
}
final String name = parser.getName();
if (TAG_REQUEST_FOCUS.equals(name)) {
} else if (TAG_TAG.equals(name)) {
} else if (TAG_INCLUDE.equals(name)) {
} else if (TAG_MERGE.equals(name)) {
} 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();
}
}
上面代碼可以看出,循環(huán)遍歷每個(gè)節(jié)點(diǎn)的tag,如果是特殊節(jié)點(diǎn)如include、merge那就不去解析View,如果是ImageView、LinearLayout等View的子類(lèi)那么我就去調(diào)用createViewFromTag實(shí)例化這個(gè)View然后添加到根節(jié)點(diǎn)去,之后再遞歸調(diào)用rInflateChildren去填充下一層級(jí)的ViewGroup,如此反復(fù)直至所有的View都已經(jīng)實(shí)例化并且添加完畢到這里我們就分析完setContentView到底做了些什么,第一次寫(xiě)源代碼分析有些生疏,大家見(jiàn)諒
