Android LayoutInflater 源碼分析及個人總結

我們經常用到的布局解析器LayoutInflater，主要在ListView或者RecycleView的Adapter中，用兩個常用方法

第一個方法是 LayoutInflater.from(context).inflate(resource, root);

第二個方法是LayoutInflater.from(context).inflate(resource, root, attachToRoot)；

第一個參數resource是布局，第二個root是父布局，第三個參數是決定是否把執行root.add(resource);

這兩個方法用一下四種用法：

LayoutInflater.from(context).inflate(R.layout.main_activity, null);

LayoutInflater.from(context).inflate(R.layout.main_activity, android.R.id.content);

LayoutInflater.from(context).inflate(R.layout.main_activity, android.R.id.content, false);

LayoutInflater.from(context).inflate(R.layout.main_activity, android.R.id.content, true);
           

先上LayoutInflater的inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)方法源碼

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;
        }
    }
           

由此可見

使用第一種方式是會在infalte中調用View temp = createViewFromTag(root, name, inflaterContext, attrs)，但不會temp.setLayoutParams(params)，是以temp;

的layoutParams為空，這是解析出來的布局的大小會有一些問題，當你在需要解析的布局中的根布局設定android:layout_width，android:layout_height不會生效；

第二種方式和第四種方式相同，會執行root.addView(temp, params)，并傳回root;

第三種方式，也會直接傳回temp,但是會執行temp.setLayoutParams(params)，這時在根布局設定android:layout_width，android:layout_height會生效。