1.activity的setcontent流程

 public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
        initWindowDecorActionBar();
    }

这里面是phonewindow调用setcontentview

@Override
    public void setContentView(int layoutResID) {
        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
        // decor, when theme attributes and the like are crystalized. Do not check the feature
        // before this happens.
        if (mContentParent == null) {
            installDecor();//1.创建 DecorView 拿到 mContentParent
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);2.将自己的xml布局加载进mContentParent里面
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }



 private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);//生成Decorview
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);返回contentParent，一些activity的系统主题在里面设置比如screen_custom_title ，R.layout.screen_simple

            // Set up decor part of UI to ignore fitsSystemWindows if appropriate.

2.AppCompatActivity的setcontentview流程

getDelegate().setContentView(layoutResID);

@Override
    public void setContentView(View v) {
        ensureSubDecor();
        ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v);
        mAppCompatWindowCallback.getWrapped().onContentChanged();
    }


 mSubDecor = createSubDecor();


createSubDecor()方法里面主要看
 // Now let's make sure that the Window has installed its decor by retrieving it
        ensureWindow();//拿到phonewindow
        mWindow.getDecorView();//也就是调用installDecor


final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
        if (windowContentView != null) {
            // There might be Views already added to the Window's content view so we need to
            // migrate them to our content view
            while (windowContentView.getChildCount() > 0) {
                final View child = windowContentView.getChildAt(0);
                windowContentView.removeViewAt(0);
                contentView.addView(child);
            }

            // Change our content FrameLayout to use the android.R.id.content id.
            // Useful for fragments.
            windowContentView.setId(View.NO_ID);
//修改contentview的id变成android.R.id.content            contentView.setId(android.R.id.content);

            // The decorContent may have a foreground drawable set (windowContentOverlay).
            // Remove this as we handle it ourselves
            if (windowContentView instanceof FrameLayout) {
                ((FrameLayout) windowContentView).setForeground(null);
            }
        }

        // Now set the Window's content view with the decor
        mWindow.setContentView(subDecor);

总结

1.activity中setcontentview流程

1.installDecor()->mDecor = generateDecor(-1)生成DecorView->mContentParent =generateLayout(mDecor);加载系统布局到Decorview，mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
--> ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);里面的@android：id/content赋值给mContentParent

2.mLayoutInflater.inflate(layoutResID, mContentParent);

2.AppCompatActivity的setcontentview流程

1.AppCompatDelegate.setContentView ->ensureSubDecor()->createSubDecor里面调用ensureWindow(); // 从Activity 那PhoneWindow，mWindow.getDecorView()里面调用installDecor()
-> final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
-> windowContentView.setId(View.NO_ID); // 将原始的 content id 置为 NO_ID
-> contentView.setId(android.R.id.content); // subDecerView R.id.action_bar_activity_content -> 置为 content
-> mWindow.setContentView(subDecor); //
-> ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);

接下来分析mLayoutInflater.inflate(layoutResID, mContentParent);

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 {
                advanceToRootNode(parser);
                final String name = parser.getName();

                if (DEBUG) {
                    System.out.println("**************************");
                    System.out.println("Creating root view: "
                            + name);
                    System.out.println("**************************");
                }
               //如果标签是MERGE到这段代码里
                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
              //主要看这句话
                    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.创建子布局，然后再调用createViewFromTag
                    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) {
                final InflateException ie = new InflateException(e.getMessage(), e);
                ie.setStackTrace(EMPTY_STACK_TRACE);
                throw ie;
            } catch (Exception e) {
                final InflateException ie = new InflateException(
                        getParserStateDescription(inflaterContext, attrs)
                        + ": " + e.getMessage(), e);
                ie.setStackTrace(EMPTY_STACK_TRACE);
                throw ie;
            } finally {
                // Don't retain static reference on context.
                mConstructorArgs[0] = lastContext;
                mConstructorArgs[1] = null;

                Trace.traceEnd(Trace.TRACE_TAG_VIEW);
            }

            return result;
        }
    }


查看主要看


 if (view == null) {
                final Object lastContext = mConstructorArgs[0];
                mConstructorArgs[0] = context;
                try {
                    if (-1 == name.indexOf('.')) {
                        //如果是线性相对等没有.的布局走这个
                        view = onCreateView(context, parent, name, attrs);
                    } else {
                       //比如androidx.constraintlayout.widget.ConstraintLayout
                        view = createView(context, name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

点击进去最后都会调用到LayoutInflater的createView方法

clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
constructor = clazz.getConstructor(mConstructorSignature);
final View view = constructor.newInstance(args);
通过反射生成view

丢两张布局图

image.png

image.png

inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) 解释
第一个是加载的资源文件
第二个父控件view
第三个是否attachToRoot里面带有addview功能，就是是否想让其处于某一个容器中

如果父控件设置为null就会使加载的子控件的父控件设置的长宽失效，子控件的大小由子控件里面的子view决定

ViewStub跟include差不多，懒加载隐藏布局，他就是一个宽高都为0的view，这里需要注意的一点是，当ViewStub被inflate到parent时，ViewStub就被remove掉了，即当前view hierarchy中不再存在ViewStub,而是使用对应的layout视图代替。