Android LayoutInflater.inflate源码分析

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="wrap_content"  android:orientation="vertical">  <TextView    android:id="@+id/id_menu_title_tv"    android:layout_width="match_parent"    android:layout_height="300dp"    android:gravity="center_vertical"    android:textColor="@android:color/black"    android:textSize="16sp"    android:text="@string/menu_item"/></LinearLayout>

convertView = mInflater.inflate(R.layout.menu_item, null);

convertView = mInflater.inflate(R.layout.menu_item, parent, false);

convertView = mInflater.inflate(R.layout.menu_item, parent, true);

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) {  // 获取当前应用的资源集合  final Resources res = getContext().getResources();  // 获取指定资源的xml解析器  final XmlResourceParser parser = res.getLayout(resource);  try {    return inflate(parser, root, attachToRoot);  } finally {    // 返回View之前关闭parser资源    parser.close();  }}

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {  synchronized (mConstructorArgs) {    // 获取上下文对象,即LayoutInflater.from传入的Context.    final Context inflaterContext = mContext;    // 根据parser构建XmlPullAttributes.    final AttributeSet attrs = Xml.asAttributeSet(parser);    // 保存之前的Context对象.    Context lastContext = (Context) mConstructorArgs[0];    // 赋值为传入的Context对象.    mConstructorArgs[0] = inflaterContext;    // 注意,默认返回的是父布局root.    View result = root;    try {      // 查找xml的开始标签.      int type;      while ((type = parser.next()) != XmlPullParser.START_TAG &&          type != XmlPullParser.END_DOCUMENT) {        // Empty      }      // 如果没有找到有效的开始标签,则抛出InflateException异常.      if (type != XmlPullParser.START_TAG) {        throw new InflateException(parser.getPositionDescription()            + ": No start tag found!");      }      // 获取控件名称.      final String name = parser.getName();      // 特殊处理merge标签      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 {        // 实例化我们传入的资源布局的view        final View temp = createViewFromTag(root, name, inflaterContext, attrs);        ViewGroup.LayoutParams params = null;        // 如果传入的parent不为空.        if (root != null) {          if (DEBUG) {            System.out.println("Creating params from root: " +                root);          }          // 创建父类型的LayoutParams参数.          params = root.generateLayoutParams(attrs);          if (!attachToRoot) {            // 如果实例化的View不需要添加到父布局上,则直接将根据父布局生成的params参数设置            // 给它即可.            temp.setLayoutParams(params);          }        }        // 递归的创建当前布局的所有控件        rInflateChildren(parser, temp, attrs, true);        // 如果传入的父布局不为null,且attachToRoot为true,则将实例化的View加入到父布局root中        if (root != null && attachToRoot) {          root.addView(temp, params);        }        // 如果父布局为null或者attachToRoot为false,则将返回值设置成我们实例化的View        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;  }}

/** * 方便调用5个参数的方法,ignoreThemeAttr的值为false. */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");  }  // Apply a theme wrapper, if allowed and one is specified.  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();  }  // 特殊处理“1995”这个标签(ps: 平时我们写xml布局文件时基本没有使用过).  if (name.equals(TAG_1995)) {    // Let's party like it's 1995!    return new BlinkLayout(context, attrs);  }  try {    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) {      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;  }}

public final View createView(String name, String prefix, AttributeSet attrs)  throws ClassNotFoundException, InflateException {  // 以View的name为key, 查询构造函数的缓存map中是否已经存在该View的构造函数.  Constructor<? extends View> constructor = sConstructorMap.get(name);  Class<? extends View> clazz = null;  try {    // 构造函数在缓存中未命中    if (constructor == null) {      // 通过类名去加载控件的字节码      clazz = mContext.getClassLoader().loadClass(prefix != null ? (prefix + name) : name).asSubClass(View.class);      // 如果有自定义的过滤器并且加载到字节码,则通过过滤器判断是否允许加载该View      if (mFilter != null && clazz != null) {        boolean allowed = mFilter.onLoadClass(clazz);        if (!allowed) {          failNotAllowed(name, prefix, attrs);        }      }      // 得到构造函数      constructor = clazz.getConstructor(mConstructorSignature);      constructor.setAccessible(true);      // 缓存构造函数      sConstructorMap.put(name, constructor);    } else {      if (mFilter != null) {        // 过滤的map是否包含了此类名        Boolean allowedState = mFilterMap.get(name);        if (allowedState == null) {          // 重新加载类的字节码          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);        }      }    }    // 实例化类的参数数组(mConstructorArgs[0]为Context, [1]为View的属性)    Object[] args = mConstructorArgs;    args[1] = attrs;    // 通过构造函数实例化View    final View view = constructor.newInstance(args);    if (View instanceof ViewStub) {      final ViewStub viewStub = (ViewStub) view;      viewStub.setLayoutInflater(cloneInContext((Context)args[0]))    }    return view;  } catch (NoSunchMethodException e) {    // ......  } catch (ClassNotFoundException e) {    // ......  } catch (Exception e) {    // ......  } finally {    // ......  }}