Darren Yuen
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LayoutInflater#inflate方法参数的作用

Posted on Edited on

日常开发中很多地方都见到了LayoutInflater.from().inflate()方法去将一个布局文件的内容填充为一个View，特别是inflate()这个方法，这个方法的参数有布局文件id，root和attachToRoot，那么这个root和attachToRoot参数有什么作用呢？

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public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {  
	synchronized (mConstructorArgs) {  

	View result = root;  
	  
	try {  
		advanceToRootNode(parser);  
		final String name = parser.getName();  
		  
		if (TAG_MERGE.equals(name)) {
		// merge标签处理  
			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  
			final View temp = createViewFromTag(root, name, inflaterContext, attrs);  
			  
			ViewGroup.LayoutParams params = null;  
			  
			if (root != null) {  
				// 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);  
				}
			} 
			  
			// Inflate all children under temp against its context.  
			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) {  
				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) {  

	} catch (Exception e) {  

	} finally {  
		// Don't retain static reference on context.  
		
	}  
	  
	return result;  
	}  
}

分析root与attachToRoot的四种组合情况，可以得出以下结论：

root null null not null not null
attachToRoot true false true false
返回创建的不会带params的view，不作为root的子view 创建出来的View没有设置params就使用，所以被创建出来的布局，最外层设置的宽高是无效的，并最终返回了创建出来的View对象 view带param添加到root中，返回root 返回创建的带params的view，不作为root的子view
  • root = null，无论attachToRoot取什么值都是一样的效果