从源码角度分析Activity#setContentView

最新推荐文章于 2022-07-15 16:53:51 发布

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最新推荐文章于 2022-07-15 16:53:51 发布 · 301 阅读

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#setContentView #源码 #Activity #DecorView #layout渲染

本文从源码角度详细分析了Android中Activity#setContentView的执行流程，涉及PhoneWindow、DecorView和layout渲染。通过源码解读，揭示了如何将布局资源解析并添加到DecorView的主容器中，帮助理解Android界面绘制的本质。

我们平时在开发的过程中将一个layout绘制出来是通过Activity#setContentView或者AppCompactActivity#setContentView，本文只分析Activity#setContentView，AppCompactActivity#setContentView可通过我的另外一篇文章了解从源码角度分析AppCompactActivity#setContentView

先来看看源码执行的流程图
在这里插入图片描述

有了上面的流程图我们对就setContentView源码调用有了个大概的框架，再来分析源码就不会小鹿乱撞了，哈哈，现在从setContentView入手来看整个绘制流程源码

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

我们点进去setContentView看看源码

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

这里的getWindow()返回的是Window的唯一实现类PhoneWindow，继续跟进PhoneWindow#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();
        } 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;
    }

这里面先调用installDecor()，然后判断有无转场动画，有转场动画执行专场动画，最终都通过LayoutInflater解析传进来的layoutResID到mContentParent，继续跟进installDecor()

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            // 注释1
            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) {
            // 注释2
            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 ((