今天就跟大家聊聊有关怎么浅析Activity的渲染过程，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。

我们提供的服务有：网站建设、成都网站设计、微信公众号开发、网站优化、网站认证、黄骅ssl等。为成百上千家企事业单位解决了网站和推广的问题。提供周到的售前咨询和贴心的售后服务，是有科学管理、有技术的黄骅网站制作公司

####以下代码基于API25

1.Activity是如何展现在我们眼前的？

我大概知道UI方面是和Window相关的，而activity的attach方法会传入一个window对象，所以就从activity的attach方法入手：

•  attach方法里会创建一个PhoneWindow

         

• activity在执行onCreate方法的时候都会执行一个方法performCreateCommon

  

•              点击setEnterActivityOptions方法：

            

          注意window.getDecorView()这个方法

/**
 * Retrieve the top-level window decor view (containing the standard
 * window frame/decorations and the client's content inside of that), which
 * can be added as a window to the window manager.
 *
 *

Note that calling this function for the first time "locks in"
 * various window characteristics as described in
 * {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}.


 *
 * @return Returns the top-level window decor view.
 */
public abstract View getDecorView();

 官方的解释是说这个方法是获取了顶层window的decorview。

 这里的window很明显是PhoneWindow,看它对getDecorView的实现。

         mDecor其实在PhoneWindow的构造方法里就已经生成了

preservedWindow向上追溯其来源：

从onCreate里其实根本就找不到activity显示相关的源码，于是只能看看其他人怎么分析的。

https://www.aliyun.com/jiaocheng/6995.html                        （道中重点）

https://www.cnblogs.com/snow-flower/p/6111599.html

https://blog.csdn.net/monkey646812329/article/details/52885835

if (r.window == null && !a.mFinished && willBeVisible) {
    r.window = r.activity.getWindow();
    View decor = r.window.getDecorView();
    decor.setVisibility(View.INVISIBLE);
    ViewManager wm = a.getWindowManager();
    WindowManager.LayoutParams l = r.window.getAttributes();
    a.mDecor = decor;
    l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
    l.softInputMode |= forwardBit;
    if (r.mPreserveWindow) {
        a.mWindowAdded = true;
        r.mPreserveWindow = false;
        // Normally the ViewRoot sets up callbacks with the Activity
        // in addView->ViewRootImpl#setView. If we are instead reusing
        // the decor view we have to notify the view root that the
        // callbacks may have changed.
        ViewRootImpl impl = decor.getViewRootImpl();
        if (impl != null) {
            impl.notifyChildRebuilt();
        }
    }
    if (a.mVisibleFromClient && !a.mWindowAdded) {
        a.mWindowAdded = true;
        wm.addView(decor, l);
    }

// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
    if (localLOGV) Slog.v(
        TAG, "Launch " + r + " mStartedActivity set");
    r.hideForNow = true;
}

看上面的源码

得到PhoneWindow对象

   r.window = r.activity.getWindow();
   
   View decor = r.window.getDecorView();

 从PhoneWindow获取DecorView并赋值给activity

    a.mDecor = decor;

通过WindowManager添加decor

wm.addView(decor, l);

这样activity就展示在我们眼前了。关于WindowManager更加底层的源码后探讨。

2.Activity的setContentView方法

/**
 * Set the activity content from a layout resource.  The resource will be
 * inflated, adding all top-level views to the activity.
 *
 * @param layoutResID Resource ID to be inflated.
 *
 * @see #setContentView(android.view.View)
 * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
 */
public void setContentView(@LayoutRes int layoutResID) {
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}

/**
 * Set the activity content to an explicit view.  This view is placed
 * directly into the activity's view hierarchy.  It can itself be a complex
 * view hierarchy.  When calling this method, the layout parameters of the
 * specified view are ignored.  Both the width and the height of the view are
 * set by default to {@link ViewGroup.LayoutParams#MATCH_PARENT}. To use
 * your own layout parameters, invoke
 * {@link #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)}
 * instead.
 *
 * @param view The desired content to display.
 *
 * @see #setContentView(int)
 * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
 */
public void setContentView(View view) {
    getWindow().setContentView(view);
    initWindowDecorActionBar();
}

/**
 * Set the activity content to an explicit view.  This view is placed
 * directly into the activity's view hierarchy.  It can itself be a complex
 * view hierarchy.
 *
 * @param view The desired content to display.
 * @param params Layout parameters for the view.
 *
 * @see #setContentView(android.view.View)
 * @see #setContentView(int)
 */
public void setContentView(View view, ViewGroup.LayoutParams params) {
    getWindow().setContentView(view, params);
    initWindowDecorActionBar();
}

/**
 * Add an additional content view to the activity.  Added after any existing
 * ones in the activity -- existing views are NOT removed.
 *
 * @param view The desired content to display.
 * @param params Layout parameters for the view.
 */
public void addContentView(View view, ViewGroup.LayoutParams params) {
    getWindow().addContentView(view, params);
    initWindowDecorActionBar();
}

 关于填充view,activity有4种方法。下面先讨论最常用的方法

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

第一步调用PhoneWindow的对应的方法（注意观察源码会发现，activity的绝大多数的方法都是在操作PhoneWindow）

第二步初始化ActionBar

先看看PhoneWindow的源码

@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();
    } 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);
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null && !isDestroyed()) {
        cb.onContentChanged();
    }
    mContentParentExplicitlySet = true;
}

最开始程序应该是走了installDecor方法

这个方法比较长，它负责的业务主要有以下几项。

• 如果decor为null，创建PhoneWindow的decor，已经存在decor则与PhoneWindow绑定。

• 如果mContentParent为null，通过decor创建mContentParent。

• 转场动画的处理

private void installDecor() {
    mForceDecorInstall = false;
    if (mDecor == null) {
        mDecor = generateDecor(-1);
        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);

        // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
        mDecor.makeOptionalFitsSystemWindows();

        final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                R.id.decor_content_parent);

        if (decorContentParent != null) {
            mDecorContentParent = decorContentParent;
            mDecorContentParent.setWindowCallback(getCallback());
            if (mDecorContentParent.getTitle() == null) {
                mDecorContentParent.setWindowTitle(mTitle);
            }

            final int localFeatures = getLocalFeatures();
            for (int i = 0; i < FEATURE_MAX; i++) {
                if ((localFeatures & (1 << i)) != 0) {
                    mDecorContentParent.initFeature(i);
                }
            }

            mDecorContentParent.setUiOptions(mUiOptions);

            if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||
                    (mIconRes != 0 && !mDecorContentParent.hasIcon())) {
                mDecorContentParent.setIcon(mIconRes);
            } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&
                    mIconRes == 0 && !mDecorContentParent.hasIcon()) {
                mDecorContentParent.setIcon(
                        getContext().getPackageManager().getDefaultActivityIcon());
                mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
            }
            if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||
                    (mLogoRes != 0 && !mDecorContentParent.hasLogo())) {
                mDecorContentParent.setLogo(mLogoRes);
            }

            // Invalidate if the panel menu hasn't been created before this.
            // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu
            // being called in the middle of onCreate or similar.
            // A pending invalidation will typically be resolved before the posted message
            // would run normally in order to satisfy instance state restoration.
            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
            if (!isDestroyed() && (st == null || st.menu == null) && !mIsStartingWindow) {
                invalidatePanelMenu(FEATURE_ACTION_BAR);
            }
        } else {
            mTitleView = (TextView) findViewById(R.id.title);
            if (mTitleView != null) {
                if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
                    final View titleContainer = findViewById(R.id.title_container);
                    if (titleContainer != null) {
                        titleContainer.setVisibility(View.GONE);
                    } else {
                        mTitleView.setVisibility(View.GONE);
                    }
                    mContentParent.setForeground(null);
                } else {
                    mTitleView.setText(mTitle);
                }
            }
        }

        if (mDecor.getBackground() == null && mBackgroundFallbackResource != 0) {
            mDecor.setBackgroundFallback(mBackgroundFallbackResource);
        }

        // Only inflate or create a new TransitionManager if the caller hasn't
        // already set a custom one.
        if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
            if (mTransitionManager == null) {
                final int transitionRes = getWindowStyle().getResourceId(
                        R.styleable.Window_windowContentTransitionManager,
                        0);
                if (transitionRes != 0) {
                    final TransitionInflater inflater = TransitionInflater.from(getContext());
                    mTransitionManager = inflater.inflateTransitionManager(transitionRes,
                            mContentParent);
                } else {
                    mTransitionManager = new TransitionManager();
                }
            }

            mEnterTransition = getTransition(mEnterTransition, null,
                    R.styleable.Window_windowEnterTransition);
            mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReturnTransition);
            mExitTransition = getTransition(mExitTransition, null,
                    R.styleable.Window_windowExitTransition);
            mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReenterTransition);
            mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null,
                    R.styleable.Window_windowSharedElementEnterTransition);
            mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReturnTransition);
            mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null,
                    R.styleable.Window_windowSharedElementExitTransition);
            mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReenterTransition);
            if (mAllowEnterTransitionOverlap == null) {
                mAllowEnterTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowEnterTransitionOverlap, true);
            }
            if (mAllowReturnTransitionOverlap == null) {
                mAllowReturnTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowReturnTransitionOverlap, true);
            }
            if (mBackgroundFadeDurationMillis < 0) {
                mBackgroundFadeDurationMillis = getWindowStyle().getInteger(
                        R.styleable.Window_windowTransitionBackgroundFadeDuration,
                        DEFAULT_BACKGROUND_FADE_DURATION_MS);
            }
            if (mSharedElementsUseOverlay == null) {
                mSharedElementsUseOverlay = getWindowStyle().getBoolean(
                        R.styleable.Window_windowSharedElementsUseOverlay, true);
            }
        }
    }
}

对上面的方法主要节点剖析

•  mContentParent = generateLayout(mDecor);

    推荐结合这篇博客Andriod中Style/Theme原理以及Activity界面文件选取过程浅析来看这个方法的源码

protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.

    TypedArray a = getWindowStyle();

    ...//根据window style设置window的属性

    WindowManager.LayoutParams params = getAttributes();

    // Non-floating windows on high end devices must put up decor beneath the system bars and
    // therefore must know about visibility changes of those.
    if (!mIsFloating && ActivityManager.isHighEndGfx()) {
        if (!targetPreL && a.getBoolean(
                R.styleable.Window_windowDrawsSystemBarBackgrounds,
                false)) {
            setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                    FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
        }
        if (mDecor.mForceWindowDrawsStatusBarBackground) {
            params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_STATUS_BAR_BACKGROUND;
        }
    }
    if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) {
        decor.setSystemUiVisibility(
                decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
    }

    if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
            >= android.os.Build.VERSION_CODES.HONEYCOMB) {
        if (a.getBoolean(
                R.styleable.Window_windowCloseOnTouchOutside,
                false)) {
            setCloseOnTouchOutsideIfNotSet(true);
        }
    }

    if (!hasSoftInputMode()) {
        params.softInputMode = a.getInt(
                R.styleable.Window_windowSoftInputMode,
                params.softInputMode);
    }

    if (a.getBoolean(R.styleable.Window_backgroundDimEnabled,
            mIsFloating)) {
        /* All dialogs should have the window dimmed */
        if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
            params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
        }
        if (!haveDimAmount()) {
            params.dimAmount = a.getFloat(
                    android.R.styleable.Window_backgroundDimAmount, 0.5f);
        }
    }

    if (params.windowAnimations == 0) {
        params.windowAnimations = a.getResourceId(
                R.styleable.Window_windowAnimationStyle, 0);
    }

    // The rest are only done if this window is not embedded; otherwise,
    // the values are inherited from our container.
    if (getContainer() == null) {
        if (mBackgroundDrawable == null) {
            if (mBackgroundResource == 0) {
                mBackgroundResource = a.getResourceId(
                        R.styleable.Window_windowBackground, 0);
            }
            if (mFrameResource == 0) {
                mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
            }
            mBackgroundFallbackResource = a.getResourceId(
                    R.styleable.Window_windowBackgroundFallback, 0);
            if (false) {
                System.out.println("Background: "
                        + Integer.toHexString(mBackgroundResource) + " Frame: "
                        + Integer.toHexString(mFrameResource));
            }
        }
        if (mLoadElevation) {
            mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
        }
        mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
        mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
    }

    // Inflate the window decor.

    int layoutResource;
    int features = getLocalFeatures();
    // System.out.println("Features: 0x" + Integer.toHexString(features));
    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        layoutResource = R.layout.screen_swipe_dismiss;
    } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleIconsDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_title_icons;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
        // System.out.println("Title Icons!");
    } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
            && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
        // Special case for a window with only a progress bar (and title).
        // XXX Need to have a no-title version of embedded windows.
        layoutResource = R.layout.screen_progress;
        // System.out.println("Progress!");
    } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
        // Special case for a window with a custom title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogCustomTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_custom_title;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
    } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
        // If no other features and not embedded, only need a title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
            layoutResource = a.getResourceId(
                    R.styleable.Window_windowActionBarFullscreenDecorLayout,
                    R.layout.screen_action_bar);
        } else {
            layoutResource = R.layout.screen_title;
        }
        // System.out.println("Title!");
    } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
        layoutResource = R.layout.screen_simple_overlay_action_mode;
    } else {
        // Embedded, so no decoration is needed.
        layoutResource = R.layout.screen_simple;
        // System.out.println("Simple!");
    }

    mDecor.startChanging();
    mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    if (contentParent == null) {
        throw new RuntimeException("Window couldn't find content container view");
    }

    if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
        ProgressBar progress = getCircularProgressBar(false);
        if (progress != null) {
            progress.setIndeterminate(true);
        }
    }

    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        registerSwipeCallbacks();
    }

    // Remaining setup -- of background and title -- that only applies
    // to top-level windows.
    if (getContainer() == null) {
        final Drawable background;
        if (mBackgroundResource != 0) {
            background = getContext().getDrawable(mBackgroundResource);
        } else {
            background = mBackgroundDrawable;
        }
        mDecor.setWindowBackground(background);

        final Drawable frame;
        if (mFrameResource != 0) {
            frame = getContext().getDrawable(mFrameResource);
        } else {
            frame = null;
        }
        mDecor.setWindowFrame(frame);

        mDecor.setElevation(mElevation);
        mDecor.setClipToOutline(mClipToOutline);

        if (mTitle != null) {
            setTitle(mTitle);
        }

        if (mTitleColor == 0) {
            mTitleColor = mTextColor;
        }
        setTitleColor(mTitleColor);
    }

    mDecor.finishChanging();

    return contentParent;
}

  下面看看PhoneWindow的setContentView中的installDecor之后的方法

//有转场动画，则做一个动画特效。
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
    final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
            getContext());
    transitionTo(newScene);
} else {
    //没有动画直接将布局inflate到mConentParent容器里
    mLayoutInflater.inflate(layoutResID, mContentParent);
}
mContentParent.requestApplyInsets();
//这个CallBack其实是在Activity里实现的
final Callback cb = getCallback();

//将布局改变以的事件回调给activity
if (cb != null && !isDestroyed()) {
    cb.onContentChanged();
}

所以由以上的源码分析我们可知，activity的setContentView会将布局inflate到PhoneWindow的decorView里，WindowManager再将decorview添加显示出来 。

看完上述内容，你们对怎么浅析Activity的渲染过程有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注创新互联行业资讯频道，感谢大家的支持。