Android View 原始碼解析(二) - LayoutInflater

摘要： 繼 Android View 原始碼解析(一) - setContentView 之後接著說 之前我們分析了setContentView方法的相關程式碼 接下來說說LayoutInflater的方法 LayoutInflater原始碼分析 與setContentView...

繼 Android View 原始碼解析(一) - setContentView 之後接著說

之前我們分析了setContentView方法的相關程式碼 接下來說說LayoutInflater的方法

LayoutInflater原始碼分析

1. 與setContentView相關

在PhoneWindow的generateLayout中呼叫了

View in = mLayoutInflater.inflate(layoutResource, null);

2. LayoutInflater中獲取例項化方法

/**
* Obtains the LayoutInflater from the given context.
*/
public static LayoutInflater from(Context context) {
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (LayoutInflater == null) {
throw new AssertionError("LayoutInflater not found.");
}
return LayoutInflater;
}

3. inflate方法相關

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}

public View inflate(XmlPullParser parser, @Nullable ViewGroup root) {
return inflate(parser, root, root != null);
}

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
if (DEBUG) {
Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
+ Integer.toHexString(resource) + ")");
}

final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}

最後發現都需要呼叫

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);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
//定義返回值 初始化傳入形參 root
View result = root;

try {
// 找到根節點
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
}

//驗證type是否為Start_Tag保證xml檔案正確
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}

//type為 root node
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)) {
//處理 merge相關
//root需要非空 且attachToRoot為空
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
//遞迴inflate 方法呼叫
rInflate(parser, root, inflaterContext, attrs, false);
} else {
//根據tag節點建立view物件
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);
}
//根據root生成LayoutParams
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
//如果attachToRoot為flase 則呼叫setLayoutParams
temp.setLayoutParams(params);
}
}

if (DEBUG) {
System.out.println("-----> start inflating children");
}
//遞迴inflate剩下的children
rInflateChildren(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非空且attachToRoot=true則將xml檔案的root view加到形參提供的root裡
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) {
//返回xml裡解析的root view
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);
//返回引數root或xml檔案裡的root view
return result;
}
}

相關inflate引數的結果

4. 相關方法解析

   在Inflate中多次被呼叫的rInflate

void rInflate(XmlPullParser parser, View parent, Context context,
AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {

final int depth = parser.getDepth();
int type;
//XmlPullParser解析器的標準解析模式
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
//找到start_tag節點
if (type != XmlPullParser.START_TAG) {
continue;
}
//獲取Name標記
final String name = parser.getName();

//private static final String TAG_REQUEST_FOCUS = "requestFocus";
//處理requestFocus
if (TAG_REQUEST_FOCUS.equals(name)) {
parseRequestFocus(parser, parent);
// private static final String TAG_TAG = "tag";
//處理tag
} else if (TAG_TAG.equals(name)) {
parseViewTag(parser, parent, attrs);
//private static final String TAG_INCLUDE = "include";
//處理include
} else if (TAG_INCLUDE.equals(name)) {
//如果是根節點則丟擲異常
if (parser.getDepth() == 0) {
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, context, parent, attrs);
//private static final String TAG_MERGE = "merge";
//處理merge merge需要是xml中的根節點
} 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);
}
}

//parent的所有子節點都處理完畢的時候回onFinishInflate方法
if (finishInflate) {
parent.onFinishInflate();
}
}
//可以新增自定義邏輯
protected void onFinishInflate() {
}

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