动态加载布局LayoutInflater.inflate()源代码解析

绝地灬酷狼 2022-06-14 06:37 201阅读 0赞

# 如何获取LayoutInflater #

获得 LayoutInflater 实例的三种方式

1.LayoutInflater inflater = getLayoutInflater(); //调用Activity的getLayoutInflater()

2.LayoutInflater localinflater =(LayoutInflater)context.getSystemService

(Context.LAYOUT_INFLATER_SERVICE);

1.  LayoutInflater inflater = LayoutInflater.from(context);

本质上都是调用方式二。

# LayoutInflater.inflate()源代码分析 #

## 1.两个参数的inflate方法。 ##

第一个参数是加载的xml布局资源，第二个是父布局。里面会调用三个参数的方法。

## 2.看一下三个参数的方法 ##

/** * Inflate a new view hierarchy from the specified xml resource. Throws * {@link InflateException} if there is an error. * * @param resource ID for an XML layout resource to load (e.g., * <code>R.layout.main_page</code>) * @param root Optional view to be the parent of the generated hierarchy (if * <em>attachToRoot</em> is true), or else simply an object that * provides a set of LayoutParams values for root of the returned * hierarchy (if <em>attachToRoot</em> is false.) * @param attachToRoot Whether the inflated hierarchy should be attached to * the root parameter? If false, root is only used to create the * correct subclass of LayoutParams for the root view in the XML. * @return The root View of the inflated hierarchy. If root was supplied and * attachToRoot is true, this is root; otherwise it is the root of * the inflated XML file. */ 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(); } }

最终会调用，inflate(parser, root, attachToRoot);方法。  
第三个参数attachToRoot是true的时候，会自动加载到第二个参数提到的父布局。

## 3.inflate(parser, root, attachToRoot);方法分析 ##

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;
                View result = root;
    
                try {
                    // Look for the root node.
                    int type;
                    while ((type = parser.next()) != XmlPullParser.START_TAG &&
                            type != XmlPullParser.END_DOCUMENT) {
                        // Empty
                    }
    
                    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, 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) {
                            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 against its context.
                        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.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 (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;
            }
        }

## 4.总结分析 ##

<1当调用两个参数的时候inflate（）

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

如果父布局不为空，那么会默认inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)第三个参数也是true。

第三个参数的作用如下；

if (root != null && attachToRoot) {
                            root.addView(temp, params);
                        }

第三个参数是空的时候，会自动添加到第二个参数的父布局中。

<2 第二个参数的作用

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);
                            }
                        }

当只有第二个参数不为空时候，view的layoutparam才有意义，否则是就是空，那么在xml在设置的高宽，margin就没有意义了，会使用默认的layoutparam,默认的layoutparam的的layout;width和layout：height都是wrap\_content。

## 5.inflate的重载方式 ##

如下四种：

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);
        }
    
    
    inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) 
    
    
    inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)

最终都会调用 inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)方法。