Android 使用LayoutInflater.Factory2建立佈局
一,解析LayoutInflater運行原理
從建立一個LayoutInflater的方式咱們能夠知道，LayoutInflater是系統提供的單例對象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);
#輸出value=true #說明LayoutInflater具備全局屬性
關於Inflate方法,主要分爲2組，但前2組最終也是經過調用後2組中的某一個方法來實現的緩存
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方法最終會調用以下方法，固然這是必然的，由於咱們須要解析這個佈局文件app
inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)
關於XmlPullParser parser解析器的獲取，Android內部採用了XmlpullParser解析xml，這種解析相似與SAX Parser技術，效率高，由於它以IO流的方式進行解析和讀取ide
咱們來看一下XmlPullParser獲取的這個實現方式佈局
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內部XmlResourceParser繼承自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();
}
實際咱們經過Resource獲取到的是XmlResourceParserspa
XmlResourceParser xml = getResources().getXml(R.xml.gateway); XmlResourceParser layout = getResources().getLayout(R.layout.fragment_main);
這裏注意，其實獲取資源的時候，都會經過XmlResourceParser，只是內部進行了必要的封裝而已，有興趣的 猿猿同窗 能夠查看Resource的實現代碼code
再來看看inflate的實現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) {
//從文檔頭文檔開始解析，這裏忽略文檔頭
}
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的過程，xml解析原本過慢，所以在開發中應該減小使用inflate，採用ViewHolder和SparseArray緩存View是一個不錯的選擇對象
對於屬性的讀取，咱們看到
XmlResourceParser parser = getResources().getLayout(resid); final AttributeSet attrs = Xml.asAttributeSet(parser);
咱們看到，使用了android.util.Xml類
public static AttributeSet asAttributeSet(XmlPullParser parser) {
return (parser instanceof AttributeSet)
? (AttributeSet) parser
: new XmlPullAttributes(parser);
}
AttributeSet 會最終被返回給View的Context
二.使用LayoutInflater.Factory2控件工廠
Android自定義控件的思想，獲取自定義屬性通常會在構造方法中，經過TypeArray和obtainStyledAttributes(resid, attrs)方法，但obtainStyledAttributes(resid, attrs)是沒有公開的方法，對於這一點要特別之處，在外部沒法得到自定屬性，除非從新使用XmlPullParser解析，從而獲得相應的數據值。
特別是對於Android MVVM開發而言，如何訪問綁定字段，對於這一問而言，咱們須要構建本身的LayoutInflater或者經過XmlPullParser解析以後與對應的view自動匹配，不事後者簡單，但效率會有所損失。
綜上，obtainStyledAttributes(resid, attrs)具備侷限性，咱們能夠利用LayoutInflater.Factory2來實現屬性的獲取和View的重建。
先看看LayoutInflater類中的createViewFromTag源碼：
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); //內部Layout，不用理會
}
try {
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs); //在這裏調用了Factory2的接口
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);//在這裏調用了Factory的接口，Factory2也繼承了Factory
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs); //私有實現的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;
}
}
咱們實現Factory2工廠便可，返回值能夠爲null,也能夠自行實現建立View，咱們這裏選擇實現建立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中調用
{
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); //建工廠設置到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); //這裏咱們調用LayoutInflater建立View的方法，固然也能夠自定義
}
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中調用,由於LayoutInflater是全局的，所以，爲了讓Activity回收正常，結束時必須調用此方法
public void release()
{
this.mInflater.setFactory2(null);
this.mInflater.setFilter(null);
this.mInflater = null;
}
public interface OnInflaterListener
{
//用於向外部提供屬性和View，咱們能夠從類外部獲取到屬性了
public void onCreateView(view,attrs);
}
}
//這裏咱們調用LayoutInflater建立View的方法，固然也能夠自定義實現本身建立方法 view = mInflater.createView(name, prefix, attrs);
public interface OnInflaterListener
{
//用於向外部提供屬性和View，咱們能夠從類外部獲取到屬性了
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)
{
//從這裏獲取attrs,裏面包含自定義屬性
}
});
三.LayoutInflater可替代方式
TextView myView = (TextView)View.inflate(context, resource, root);
相關文章
- 1. Android動態建立佈局經常使用方法
- 2. element建立佈局
- 3. Android UI開發（佈局的建立）
- 4. Android Window佈局建立流程分析
- 5. Android 經常使用佈局
- 6. SharePoint 建立頁面佈局
- 7. 使用android studio建立Activity
- 8. 淺析inline-block--使用inline-block建立佈局
- 9. 使用佈局
- 10. jQuery EasyUI 佈局 - 爲網頁建立邊框佈局
- 更多相關文章...
- • ASP.NET Web Pages - 頁面佈局 - ASP.NET 教程
- • ASP.NET MVC - 樣式和佈局 - ASP.NET 教程
- • Composer 安裝與使用
- • 適用於PHP初學者的學習線路和建議
相關標籤/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
最新文章
歡迎關注本站公眾號,獲取更多信息
