Android Q : 安卓源码、水滴屏适配状态栏图标（图标过多时显示一个点）

源码路径：com.android.systemui.statusbar.phone/StatusIconContainer.java
布局文件路径：SystemUI/res/layout/status_bar.xml
下拉后状态栏布局文件路径：SystemUI/res/layout/quick_qs_status_icons.xml
锁屏状态栏文件布局：SystemUI/res/layout/keyguard_status_bar.xml

一、状态栏布局

在没下拉状态栏时，原生android会将状态栏分为两部分（如下图及布局源码）
1、android:id=“@+id/notification_icon_area
2、android:id=”@+id/system_icon_area"
从下面的布局文件可以看到这两块区域的权重都是1，左边放通知图标，右边放系统图标，中间留有一块控件用来放缺口（也就是水滴或刘海的位置），在这里如果没有水滴的话可以修改权重，来放置更多的系统图标或通知图标（有水滴的话改了图标过多时就会遮挡住图标）

<FrameLayoutandroid:layout_height="match_parent"android:layout_width="0dp"android:layout_weight="1"><include layout="@layout/heads_up_status_bar_layout" /><!-- The alpha of the left side is controlled by PhoneStatusBarTransitions, and theindividual views are controlled by StatusBarManager disable flags DISABLE_CLOCK andDISABLE_NOTIFICATION_ICONS, respectively --><LinearLayoutandroid:id="@+id/status_bar_left_side"android:layout_height="match_parent"android:layout_width="match_parent"android:clipChildren="false"><ViewStubandroid:id="@+id/operator_name"android:layout_width="wrap_content"android:layout_height="match_parent"android:layout="@layout/operator_name" /><com.android.systemui.statusbar.phone.StatusIconContainer android:id="@+id/statusIcons_left"android:layout_width="wrap_content"android:layout_height="match_parent"android:paddingEnd="@dimen/signal_cluster_battery_padding"android:gravity="center_vertical"android:orientation="horizontal"/><com.android.systemui.statusbar.AlphaOptimizedFrameLayoutandroid:id="@+id/notification_icon_area"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:orientation="horizontal"android:clipChildren="false"/></LinearLayout></FrameLayout><!-- Space should cover the notch (if it exists) and let other views lay out around it --><android.widget.Spaceandroid:id="@+id/cutout_space_view"android:layout_width="0dp"android:layout_height="match_parent"android:gravity="center_horizontal|center_vertical"/><com.android.systemui.statusbar.AlphaOptimizedFrameLayoutandroid:id="@+id/centered_icon_area"android:layout_width="wrap_content"android:layout_height="match_parent"android:orientation="horizontal"android:clipChildren="false"android:gravity="center_horizontal|center_vertical"/><com.android.keyguard.AlphaOptimizedLinearLayout android:id="@+id/system_icon_area"android:layout_width="0dp"android:layout_height="match_parent"android:layout_weight="1"android:orientation="horizontal"android:gravity="center_vertical|end"><LinearLayoutandroid:id="@+id/system_icons"android:layout_width="match_parent"android:layout_height="match_parent"android:gravity="center_vertical"><com.android.systemui.statusbar.phone.StatusIconContainer android:id="@+id/statusIcons"android:layout_width="0dp"android:layout_weight="1"android:layout_height="match_parent"android:paddingEnd="@dimen/signal_cluster_battery_padding"android:gravity="center_vertical"android:orientation="horizontal"/><com.android.systemui.BatteryMeterView android:id="@+id/battery"android:layout_height="match_parent"android:layout_width="wrap_content"android:clipToPadding="false"android:clipChildren="false"android:textAppearance="@style/TextAppearance.StatusBar.Clock" /><android.widget.Spaceandroid:layout_width="2dp"android:layout_height="match_parent"/><com.android.systemui.statusbar.policy.Clockandroid:id="@+id/clock"android:layout_width="wrap_content"android:layout_height="match_parent"android:textAppearance="@style/TextAppearance.StatusBar.Clock"android:paddingBottom="2dip"android:singleLine="true"android:gravity="center_vertical|end"/></LinearLayout></com.android.keyguard.AlphaOptimizedLinearLayout>

二、状态栏右侧系统图标显示过多时显示一个点

在源码中，控制右侧系统图标显示的有两个限制：
1、图标个数
2、宽度限制
主要方法：onMeasure 和 calculateIconTranslations （下方贴上源代码）
在onMeasure中会测量水滴右边区域能放的下的图标的总宽度（totalWidth）
在calculateIconTranslations中会判断如果图标个数大于限定个数并且剩余宽度不足以绘制一个图标时，就去绘制那个点，达到开始那张图的效果

// Max 8 status icons including batteryprivate static final int MAX_ICONS = 7;

安卓原生定义了最大显示图标个数是8个（包括电池图标）

mUnderflowWidth ：显示的点标框的宽度
mShouldRestrictIcons：是否需要限制图标的一个标志位，原生代码中的下拉后的状态栏是不限制图标的，就是在QuickStatusBarHeaderController.java中控制这个变量为false后就不会去画点

@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {mMeasureViews.clear();int mode = MeasureSpec.getMode(widthMeasureSpec);final int width = MeasureSpec.getSize(widthMeasureSpec);//当前View的宽度final int count = getChildCount();// Collect all of the views which want to be laid outfor (int i = 0; i < count; i++) {StatusIconDisplayable icon = (StatusIconDisplayable) getChildAt(i);if (icon.isIconVisible() && !icon.isIconBlocked()&& !mIgnoredSlots.contains(icon.getSlot())) {mMeasureViews.add((View) icon);}}int visibleCount = mMeasureViews.size();int maxVisible = visibleCount <= MAX_ICONS ? MAX_ICONS : MAX_ICONS - 1;int totalWidth = mPaddingLeft + mPaddingRight;boolean trackWidth = true;// Measure all children so that they report the correct widthint childWidthSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.UNSPECIFIED);mNeedsUnderflow = mShouldRestrictIcons && visibleCount > MAX_ICONS;for (int i = 0; i < mMeasureViews.size(); i++) {// Walking backwardsView child = mMeasureViews.get(visibleCount - i - 1);measureChild(child, childWidthSpec, heightMeasureSpec);// mShouldRestrictIcons：是否限制图标的一个判断，原生代码中的下拉后的状态栏是//不限制图标的，就是在QuickStatusBarHeaderController.java中控制这个变量if (mShouldRestrictIcons) {  if (i < maxVisible && trackWidth) {//把不超过最大个数的所有图标的宽度加起来totalWidth += getViewTotalMeasuredWidth(child);} else if (trackWidth) {// We've hit the icon limit; add space for dots//mUnderflowWidth：最后加上圆点的宽度totalWidth += mUnderflowWidth;trackWidth = false;}} else {totalWidth += getViewTotalMeasuredWidth(child);}}if (mode == MeasureSpec.EXACTLY) {//如果图标个数没有超过最大限制的数量但是图标的总宽度大于View的宽度//此时也是需要显示点的，将mNeedsUnderflow 设置为trueif (!mNeedsUnderflow && totalWidth > width) {mNeedsUnderflow = true;}setMeasuredDimension(width, MeasureSpec.getSize(heightMeasureSpec));} else {if (mode == MeasureSpec.AT_MOST && totalWidth > width) {mNeedsUnderflow = true;totalWidth = width;}setMeasuredDimension(totalWidth, MeasureSpec.getSize(heightMeasureSpec));}}

private void calculateIconTranslations() {mLayoutStates.clear();float width = getWidth();//总宽度减去PaddingEnd，获取不显示图标时最大的X偏移量float translationX = width - getPaddingEnd();float contentStart = getPaddingStart();//获取当前需要显示的图标个数int childCount = getChildCount();// Underflow === don't show content until that indexif (DEBUG) android.util.Log.d(TAG, "calculateIconTranslations: start=" + translationX+ " width=" + width + " underflow=" + mNeedsUnderflow);// Collect all of the states which want to be visiblefor (int i = childCount - 1; i >= 0; i--) {View child = getChildAt(i);StatusIconDisplayable iconView = (StatusIconDisplayable) child;StatusIconState childState = getViewStateFromChild(child);if (!iconView.isIconVisible() || iconView.isIconBlocked()|| mIgnoredSlots.contains(iconView.getSlot())) {//满足以上条件设置图标状态为隐藏childState.visibleState = STATE_HIDDEN;if (DEBUG) Log.d(TAG, "skipping child (" + iconView.getSlot() + ") not visible");continue;}//设置图标状态为显示childState.visibleState = STATE_ICON;//总X偏移量减去图标的宽度，己算当前图标的X轴偏移量，//如果此时计算结果为负数，则说明View中剩余的宽度不足以将此图标显示完全childState.xTranslation = translationX - getViewTotalWidth(child);mLayoutStates.add(0, childState);translationX -= getViewTotalWidth(child);}// Show either 1-MAX_ICONS icons, or (MAX_ICONS - 1) icons + overflowint totalVisible = mLayoutStates.size();int maxVisible = totalVisible <= MAX_ICONS ? MAX_ICONS : MAX_ICONS - 1;mUnderflowStart = 0;int visible = 0;int firstUnderflowIndex = -1;for (int i = totalVisible - 1; i >= 0; i--) {StatusIconState state = mLayoutStates.get(i);// Allow room for underflow if we found we need it in onMeasure//如果需要画点，并且当前图标的X偏移量小于点标框的宽度+padding时，记录当前图标的下标if (mNeedsUnderflow && (state.xTranslation < (contentStart + mUnderflowWidth))||(mShouldRestrictIcons && visible >= maxVisible)) {firstUnderflowIndex = i;break;}mUnderflowStart = (int) Math.max(contentStart, state.xTranslation - mUnderflowWidth);visible++;}if (firstUnderflowIndex != -1) {int totalDots = 0;int dotWidth = mStaticDotDiameter + mDotPadding;int dotOffset = mUnderflowStart + mUnderflowWidth - mIconDotFrameWidth;for (int i = firstUnderflowIndex; i >= 0; i--) {//拿到当前下标的图标状态StatusIconState state = mLayoutStates.get(i);//系统定义的MAX_DOTS=1，也就是说点图标只会显示一个if (totalDots < MAX_DOTS) {state.xTranslation = dotOffset;//设置当前图标状态为点图标state.visibleState = STATE_DOT;dotOffset -= dotWidth;totalDots++;} else {//剩余的图标状态都设置为隐藏state.visibleState = STATE_HIDDEN;}}}// Stole this from NotificationIconContainer. Not optimal but keeps the layout logic cleanif(isLayoutRtl()) {for (int i = 0; i < childCount; i++) {View child = getChildAt(i);StatusIconState state = getViewStateFromChild(child);state.xTranslation = width - state.xTranslation - child.getWidth();}}}