Activity界面繪製過程詳解
設置界面首先就是Activity.setContentView()方法：我們先看一下他的源碼：
/**
* 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(int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}getWindow()就是獲取該頁面的窗體Window，該類是一個抽象類，他有一個唯一的子類PhoneWindow.
/**
* Retrieve the current {@link android.view.Window} for the activity.
* This can be used to directly access parts of the Window API that
* are not available through Activity/Screen.
*
* @return Window The current window, or null if the activity is not
* visual.
*/
public Window getWindow() {
return mWindow;
}接下來，我們看一下PhoneWindow.setContentView()方法。(簡單的理解是PhoneWindow把DectorView(FrameLayout的子類)進行包裝，將它作爲窗口的根View)
@Override
public void setContentView(int layoutResID) {
// mContentParent 是當前window顯示內容的父佈局，它只能是mDecor或mDecor的子View,如果mContentParent爲null，說明是第一次調用setContentView方法
// 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) {
// 內部會創建mContentParent, 如果mDecor爲null就創建，然後如果mContentParent爲null，就根據當前要顯示的主題去添加對應的佈局，
// 並把該佈局中id爲content的ViewGroup賦值給mContentParent。
installDecor();
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
// 多次調用setContentView，可能是第二次、第三次，先把之前的頁面內容移除
mContentParent.removeAllViews();
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {
// 把佈局inflate後添加到mContentParent中
mLayoutInflater.inflate(layoutResID, mContentParent);
}
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}上面簡單的說明了installDecor()的作用，這裏我們在源碼中仔細說明一下, 通過這個源碼
我們知道設置主題要在setContentView()之前去調用，如用代碼設置requestWindowFeature()設置主題時要在setContentView()之前設置纔有用.
private void installDecor() {
if (mDecor == null) {
// 內部就是new 一個 DecorView
mDecor = generateDecor();
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
}
if (mContentParent == null) {
// 根據當前主題去選擇對應的佈局文件，然後把佈局中的id=content(一般爲FrameLayout)部分賦值給mContentParent.
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)) {
invalidatePanelMenu(FEATURE_ACTION_BAR);
}
} else {
mTitleView = (TextView)findViewById(R.id.title);
if (mTitleView != null) {
mTitleView.setLayoutDirection(mDecor.getLayoutDirection());
if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
View titleContainer = findViewById(
R.id.title_container);
if (titleContainer != null) {
titleContainer.setVisibility(View.GONE);
} else {
mTitleView.setVisibility(View.GONE);
}
if (mContentParent instanceof FrameLayout) {
((FrameLayout)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);
}
}
}
}我們先看一下generateLayout的源碼：
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
TypedArray a = getWindowStyle();
if (false) {
System.out.println("From style:");
String s = "Attrs:";
for (int i = 0; i < R.styleable.Window.length; i++) {
s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
+ a.getString(i);
}
System.out.println(s);
}
mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
& (~getForcedWindowFlags());
if (mIsFloating) {
setLayout(WRAP_CONTENT, WRAP_CONTENT);
setFlags(0, flagsToUpdate);
} else {
setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
}
if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
requestFeature(FEATURE_NO_TITLE);
} else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
// Don't allow an action bar if there is no title.
requestFeature(FEATURE_ACTION_BAR);
}
if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
requestFeature(FEATURE_ACTION_BAR_OVERLAY);
}
if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
requestFeature(FEATURE_ACTION_MODE_OVERLAY);
}
if (a.getBoolean(R.styleable.Window_windowSwipeToDismiss, false)) {
requestFeature(FEATURE_SWIPE_TO_DISMISS);
}
if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
}
if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,
false)) {
setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
& (~getForcedWindowFlags()));
}
if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
false)) {
setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
& (~getForcedWindowFlags()));
}
if (a.getBoolean(R.styleable.Window_windowOverscan, false)) {
setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));
}
if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {
setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
}
if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,
getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB)) {
setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
}
a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {
if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
a.getValue(R.styleable.Window_windowFixedWidthMajor,
mFixedWidthMajor);
}
if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {
if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
a.getValue(R.styleable.Window_windowFixedWidthMinor,
mFixedWidthMinor);
}
if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {
if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
a.getValue(R.styleable.Window_windowFixedHeightMajor,
mFixedHeightMajor);
}
if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {
if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
a.getValue(R.styleable.Window_windowFixedHeightMinor,
mFixedHeightMinor);
}
if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {
requestFeature(FEATURE_CONTENT_TRANSITIONS);
}
if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) {
requestFeature(FEATURE_ACTIVITY_TRANSITIONS);
}
final WindowManager windowService = (WindowManager) getContext().getSystemService(
Context.WINDOW_SERVICE);
if (windowService != null) {
final Display display = windowService.getDefaultDisplay();
final boolean shouldUseBottomOutset =
display.getDisplayId() == Display.DEFAULT_DISPLAY
|| (getForcedWindowFlags() & FLAG_FULLSCREEN) != 0;
if (shouldUseBottomOutset && a.hasValue(R.styleable.Window_windowOutsetBottom)) {
if (mOutsetBottom == null) mOutsetBottom = new TypedValue();
a.getValue(R.styleable.Window_windowOutsetBottom,
mOutsetBottom);
}
}
final Context context = getContext();
final int targetSdk = context.getApplicationInfo().targetSdkVersion;
final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB;
final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH;
final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP;
final boolean targetHcNeedsOptions = context.getResources().getBoolean(
R.bool.target_honeycomb_needs_options_menu);
final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE);
if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) {
addFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);
} else {
clearFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);
}
// 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 (!mForcedStatusBarColor) {
mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
}
if (!mForcedNavigationBarColor) {
mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
}
if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB) {
if (a.getBoolean(
R.styleable.Window_windowCloseOnTouchOutside,
false)) {
setCloseOnTouchOutsideIfNotSet(true);
}
}
WindowManager.LayoutParams params = getAttributes();
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));
}
}
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);
}
// 上面的那一塊都是對Activity中設置的主題進行判斷。下面就是根據不同的主題，選擇不同的佈局文件。
// 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();
// inflate對應的佈局文件，並添加到mDecor中。
View in = mLayoutInflater.inflate(layoutResource, null);
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
mContentRoot = (ViewGroup) in;
// 找到佈局中android:id="@android:id/content"。的ViewGroup賦值給contentParent,一般是FrameLayout
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;
} 上面看到有很多相應主題的佈局文件，我們就以典型的R.layout.screen_title爲例看一下。
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:fitsSystemWindows="true">
<!-- Popout bar for action modes -->
<ViewStub android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="?attr/actionBarTheme" />
// 標題
<FrameLayout
android:layout_width="match_parent"
android:layout_height="?android:attr/windowTitleSize"
style="?android:attr/windowTitleBackgroundStyle">
<TextView android:id="@android:id/title"
style="?android:attr/windowTitleStyle"
android:background="@null"
android:fadingEdge="horizontal"
android:gravity="center_vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</FrameLayout>
// 頁面內容
<FrameLayout android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>看到這裏基本差不多了，我們就以第一次調用setContentView方法爲例總結一下整體的流程。
- 第一次調用setContentView()方法時會去創建一個DecorView，這就是整個窗口的根佈局。
- 接着回去根據我們設置的對應主題，來加載與之對應的佈局文件並將其添加到DecorView中，然後找到該佈局中id=content的ViewGroup賦值給mContentParent。
- 將我們要設置的Activity對應的佈局添加到mContentParent中。
