从源码角度分析Activity#setContentView
我们平时在开发的过程中将一个layout绘制出来是通过Activity#setContentView
先来看看源码执行的流程图
image.png
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1
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 = 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);
}
}
}
}
我们先来看看注释1的地方，mDecor就是DecorView，是顶层布局容器并继承FrameLayout，通过generateDecor(-1)来生成，继续跟进generateDecor(-1)
protected DecorView generateDecor(int featureId) {
// System process doesn't have application context and in that case we need to directly use
// the context we have. Otherwise we want the application context, so we don't cling to the
// activity.
Context context;
if (mUseDecorContext) {
Context applicationContext = getContext().getApplicationContext();
if (applicationContext == null) {
context = getContext();
} else {
context = new DecorContext(applicationContext, getContext());
if (mTheme != -1) {
context.setTheme(mTheme);
}
}
} else {
context = getContext();
}
return new DecorView(context, featureId, this, getAttributes());
}
可以看到在这里创建了上下文Context对象，最终通过DecorView的构造函数创建DecorView对象并返回。
再回到installDecor()方法中，看到注释2的位置，如果mContentParent为null，则调用generateLayout(mDecor)并将返回值赋值给mContentParent，跟进generateLayout(mDecor)，由于代码太多，我们只截取关键代码讲解
protected ViewGroup generateLayout(DecorView decor) {
...
// 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;
setCloseOnSwipeEnabled(true);
} 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);
...
}
这段代码根据应用不同的主题将对应的布局文件id赋值给layoutResource，并将mLayoutInflater和layoutResource传入DecorView#onResourcesLoaded，跟进onResourcesLoaded()
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
if (mBackdropFrameRenderer != null) {
loadBackgroundDrawablesIfNeeded();
mBackdropFrameRenderer.onResourcesLoaded(
this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
getCurrentColor(mNavigationColorViewState));
}
mDecorCaptionView = createDecorCaptionView(inflater);
// 注释3
final View root = inflater.inflate(layoutResource, null);
if (mDecorCaptionView != null) {
if (mDecorCaptionView.getParent() == null) {
addView(mDecorCaptionView,
new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mDecorCaptionView.addView(root,
new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
} else {
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
可以看到注释3，通过解析layoutResource创建一个root对象，最后通过addView()将root对象添加到DecorView中，了解onResourcesLoaded()做的事情后，继续回到PhoneWindow#generateLayout，截取其中部分代码
protected ViewGroup generateLayout(DecorView decor) {
...
mDecor.startChanging();
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
// 注释4
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
...
return contentParent;
}
可以看到注释4出的代码，通过findViewById得到contentParent，ID_ANDROID_CONTENT常量值为com.android.internal.R.id.content，这个id是主容器的id并且是一定存在的，最后返回contentParent，好，总结下generateLayout方法做的事情：根据不同的主题获取了不同的layoutResource，通过onResourcesLoaded方法将layoutResource解析，并将解析得到的View添加到DecorView，最后通过View的id com.android.internal.R.id.content得到contentParent并将其返回
回到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;
}
通过上面的源码分析我们可以发现，installDecor()里面调用generateLayout()给mContentParent赋值，即mContentParent就是id为com.android.internal.R.id.content容器，最后将我们传入setContentView()中的layoutResID渲染出来放到mContentParent容器中
视图结构图如下：
image.png
screen_simple.xml代码如下：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
25 android:layout_width="match_parent"
26 android:layout_height="match_parent"
27 android:fitsSystemWindows="true"
28 android:orientation="vertical">
29 <ViewStub android:id="@+id/action_mode_bar_stub"
30 android:inflatedId="@+id/action_mode_bar"
31 android:layout="@layout/action_mode_bar"
32 android:layout_width="match_parent"
33 android:layout_height="wrap_content"
34 android:theme="?attr/actionBarTheme" />
35 <FrameLayout
36 android:id="@android:id/content"
37 android:layout_width="match_parent"
38 android:layout_height="match_parent"
39 android:foregroundInsidePadding="false"
40 android:foregroundGravity="fill_horizontal|top"
41 android:foreground="?android:attr/windowContentOverlay" />
42</LinearLayout>
网友评论