序言
17年上半年主要做车机项目SystemUI的工作，一般的来说可以选择在源码的基础上定制，也可以重新编写。具体选择哪种方案，也要根据自身项目的需求和工作量来考虑，但是不管选择哪种，都需要对SystemUI源码有一定的了解。本文主要先从大体上了解整个SystemUI的运行机制，然后再从状态栏的图标如何显示，下拉菜单是如何的实现，来剖析这个模块的运行原理，最后用一个需求来深入的了解SystemUI模块。希望能够帮助有这方面需求的同学，当然了，本文都是笔者自己对代码的理解，如果有不正确的地方，欢迎留言指出！
整体架构
相信很多没有了解过SystemUI的同学都觉得它很神秘，因为这个Application很特殊，它和系统的联系很紧密，而且需要在源码的环境下编译，所以这也是和应用开发者关系比较疏远的原因之一。下图是SystemUI的整体架构图，我看过Android 4.4和6.0的代码，虽然代码变化很大，但是原理和核心代码都是差不多的。
SystemUI的启动是由SystemServer进程来操作的，在整个系统资源，服务加载完成差不多的时候，调用了startSystemUI() 来启动一个服务SystemUIService ，此时就进入了SystemUI的应用程序世界了。
static final void startSystemUi(Context context) {
Intent intent = new Intent();
intent.setComponent(new ComponentName("com.android.systemui",
"com.android.systemui.SystemUIService"));
//Slog.d(TAG, "Starting service: " + intent);
context.startServiceAsUser(intent, UserHandle.OWNER);
}首先来说下一个aidl文件，叫做IStatusBar.aidl，它的路径在frameworks/base/core/java/com/android/internal/statusbar 下。它是framework和SystemUI的通信接口，包括我们的StatusBarManagerService封装的也是这个接口。我们的SystemUI主要是显示系统状态的改变，一般的由内部和外部导致，比如系统电量的改变，SystemUI会接收系统广播来修改，这种一般不会暴露给外部使用，不然就导致显示异常，还有种是外部导致SystemUI显示的变化，像其他应用发来通知，隐藏状态栏等，这个就需要我们的IStatusBar.aidl来承担之间的通信规则了。当我们的SystemSever进程来启动我们的SystemUIService，我们SystemUIService会启动很多的类，而这些类都是继承SystemUI接口的，并且都是有自己的职责所在。
/**
* Makes sure that all the SystemUI services are running. If they are already running, this is a
* no-op. This is needed to conditinally start all the services, as we only need to have it in
* the main process.
*
* <p>This method must only be called from the main thread.</p>
*/
public void startServicesIfNeeded() {
if (mServicesStarted) {
return;
}
if (!mBootCompleted) {
// check to see if maybe it was already completed long before we began
// see ActivityManagerService.finishBooting()
if ("1".equals(SystemProperties.get("sys.boot_completed"))) {
mBootCompleted = true;
if (DEBUG) Log.v(TAG, "BOOT_COMPLETED was already sent");
}
}
Log.v(TAG, "Starting SystemUI services.");
final int N = SERVICES.length;
for (int i=0; i<N; i++) {
Class<?> cl = SERVICES[i];
if (DEBUG) Log.d(TAG, "loading: " + cl);
try {
mServices[i] = (SystemUI)cl.newInstance();
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InstantiationException ex) {
throw new RuntimeException(ex);
}
mServices[i].mContext = this;
mServices[i].mComponents = mComponents;
if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
mServices[i].start();
if (mBootCompleted) {
mServices[i].onBootCompleted();
}
}
mServicesStarted = true;
}
下面是启动的所有接口，
/**
* The classes of the stuff to start.
*/
private final Class<?>[] SERVICES = new Class[] {
com.android.systemui.tuner.TunerService.class,
com.android.systemui.keyguard.KeyguardViewMediator.class,
com.android.systemui.recents.Recents.class,
com.android.systemui.volume.VolumeUI.class,
com.android.systemui.statusbar.SystemBars.class,
com.android.systemui.usb.StorageNotification.class,
com.android.systemui.power.PowerUI.class,
com.android.systemui.media.RingtonePlayer.class,
com.android.systemui.keyboard.KeyboardUI.class,
};
我们这里只研究下主要试图的部分，也就是我们的SystemBars，这个类主要的工作就是通过类加载器生成我们的PhoneStatusBar，然后调用它的start()方法，我们切换到PhoneStatusBar这个类来，PhoneStatusBar这个类承担了最主要的添加，移除，更新视图的重任，它负责解析状态栏，导航栏的布局文件，然后通过WindowManagerService来生成Ｗindow对象，它实现了IStatusBar的所有接口，负责接收外界所有的关于SystemUI视图更新的消息。
视图
视图这块主要有三个模块分别是状态栏，导航栏，还有下拉模块。状态栏主要显示系统的状态，导航栏一般提供了快捷Home，最近打开的应用，和回到上一层，下拉菜单提供了一些快捷操作，通知的显示，这里就不讲导航栏了，感兴趣可以自行了解。来看看状态栏吧，小小的一个区域，Google却把它封装成一层又一层的，整个statusbar布局可以说是非常复杂，不花点精力真的不知道哪对哪。
statusbar的整体结构可以简化如上图所示，statusbar的图标显示在PhoneStatusBarView 那一层，其中又包裹着moreIcons和notificationIcons，下面是6.0的布局文件。
<com.android.systemui.statusbar.phone.PhoneStatusBarView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:systemui="http://schemas.android.com/apk/res/com.android.systemui"
android:id="@+id/status_bar"
android:background="@drawable/system_bar_background"
android:orientation="vertical"
android:focusable="false"
android:descendantFocusability="afterDescendants"
>
<ImageView
android:id="@+id/notification_lights_out"
android:layout_width="@dimen/status_bar_icon_size"
android:layout_height="match_parent"
android:paddingStart="6dip"
android:paddingBottom="2dip"
android:src="@drawable/ic_sysbar_lights_out_dot_small"
android:scaleType="center"
android:visibility="gone"
/>
<LinearLayout android:id="@+id/status_bar_contents"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingStart="6dp"
android:paddingEnd="8dp"
android:orientation="horizontal"
>
<com.android.systemui.statusbar.AlphaOptimizedFrameLayout
android:id="@+id/notification_icon_area"
android:layout_width="0dip"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal"
>
<!-- The alpha of this area is both controlled from PhoneStatusBarTransitions and
PhoneStatusBar (DISABLE_NOTIFICATION_ICONS), so we need two views here. -->
<com.android.keyguard.AlphaOptimizedLinearLayout
android:id="@+id/notification_icon_area_inner"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<com.android.systemui.statusbar.StatusBarIconView android:id="@+id/moreIcon"
android:layout_width="@dimen/status_bar_icon_size"
android:layout_height="match_parent"
android:src="@drawable/stat_notify_more"
android:visibility="gone"
/>
<com.android.systemui.statusbar.phone.IconMerger android:id="@+id/notificationIcons"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentStart="true"
android:gravity="center_vertical"
android:orientation="horizontal"/>
</com.android.keyguard.AlphaOptimizedLinearLayout>
</com.android.systemui.statusbar.AlphaOptimizedFrameLayout>
<com.android.keyguard.AlphaOptimizedLinearLayout android:id="@+id/system_icon_area"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:orientation="horizontal"
>
<include layout="@layout/system_icons" />
<com.android.systemui.statusbar.policy.Clock
android:id="@+id/clock"
android:textAppearance="@style/TextAppearance.StatusBar.Clock"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:singleLine="true"
android:paddingStart="7dp"
android:gravity="center_vertical|start"
/>
</com.android.keyguard.AlphaOptimizedLinearLayout>
</LinearLayout>
</com.android.systemui.statusbar.phone.PhoneStatusBarView>我们一般动态显示的图标在标签下system_icons布局中，
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/system_icons"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center_vertical">
<com.android.keyguard.AlphaOptimizedLinearLayout android:id="@+id/statusIcons"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:gravity="center_vertical"
android:orientation="horizontal"/>
<include layout="@layout/signal_cluster_view"
android:id="@+id/signal_cluster"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="2.5dp"/>
<!-- battery must be padded below to match assets -->
<com.android.systemui.BatteryMeterView android:id="@+id/battery"
android:layout_height="14.5dp"
android:layout_width="9.5dp"
android:layout_marginBottom="@dimen/battery_margin_bottom"/>
</LinearLayout>可以看到电池电量和信号是专门的控件去处理的，因为这块是一直显示在我们的状态栏上的，并且由系统去修改的，上面也提到了，这个是不提供外界修改的接口。其他的图标的更新是在id叫statusIcons的一个线性布局中，代码控制模块是通过CommandQueue将回调传递给PhoneStatusBar，然后PhoneStatusBar又交给StatusBarIconController中，以下是部分代码
public void addSystemIcon(String slot, int index, int viewIndex, StatusBarIcon icon) {
boolean blocked = mIconBlacklist.contains(slot);
StatusBarIconView view = new StatusBarIconView(mContext, slot, null, blocked);
view.set(icon);
mStatusIcons.addView(view, viewIndex, new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, mIconSize));
view = new StatusBarIconView(mContext, slot, null, blocked);
view.set(icon);
mStatusIconsKeyguard.addView(view, viewIndex, new LinearLayout.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT, mIconSize));
applyIconTint();
}
public void updateSystemIcon(String slot, int index, int viewIndex,
StatusBarIcon old, StatusBarIcon icon) {
StatusBarIconView view = (StatusBarIconView) mStatusIcons.getChildAt(viewIndex);
view.set(icon);
view = (StatusBarIconView) mStatusIconsKeyguard.getChildAt(viewIndex);
view.set(icon);
applyIconTint();
}
public void removeSystemIcon(String slot, int index, int viewIndex) {
mStatusIcons.removeViewAt(viewIndex);
mStatusIconsKeyguard.removeViewAt(viewIndex);
}mStatusIcons对应的就是前面介绍的id为statusIcons的布局。我们再来分析下下拉菜单的原理机制，当我们触摸手机的状态栏的位置，下拉菜单会随着我们手势做相应的处理。还记得我们状态栏最外层布局节点是PhoneStatusBarView,
@Override
public boolean onTouchEvent(MotionEvent event) {
boolean barConsumedEvent = mBar.interceptTouchEvent(event);
if (DEBUG_GESTURES) {
if (event.getActionMasked() != MotionEvent.ACTION_MOVE) {
EventLog.writeEvent(EventLogTags.SYSUI_PANELBAR_TOUCH,
event.getActionMasked(), (int) event.getX(), (int) event.getY(),
barConsumedEvent ? 1 : 0);
}
}
return barConsumedEvent || super.onTouchEvent(event);
}首先先看看mBar是否要拦截这个事件，如果没有拦截则调用父类的onTouchEvent()方法，这里的mBar其实就是PhoneStatusBar这个类，这个类相当于一个控制器的作用，再看看PhoneStatusBar什么时候会拦截这个事件，
public boolean interceptTouchEvent(MotionEvent event) {
if (DEBUG_GESTURES) {
if (event.getActionMasked() != MotionEvent.ACTION_MOVE) {
EventLog.writeEvent(EventLogTags.SYSUI_STATUSBAR_TOUCH,
event.getActionMasked(), (int) event.getX(), (int) event.getY(),
mDisabled1, mDisabled2);
}
}
if (SPEW) {
Log.d(TAG, "Touch: rawY=" + event.getRawY() + " event=" + event + " mDisabled1="
+ mDisabled1 + " mDisabled2=" + mDisabled2 + " mTracking=" + mTracking);
} else if (CHATTY) {
if (event.getAction() != MotionEvent.ACTION_MOVE) {
Log.d(TAG, String.format(
"panel: %s at (%f, %f) mDisabled1=0x%08x mDisabled2=0x%08x",
MotionEvent.actionToString(event.getAction()),
event.getRawX(), event.getRawY(), mDisabled1, mDisabled2));
}
}
if (DEBUG_GESTURES) {
mGestureRec.add(event);
}
if (mStatusBarWindowState == WINDOW_STATE_SHOWING) {
final boolean upOrCancel =
event.getAction() == MotionEvent.ACTION_UP ||
event.getAction() == MotionEvent.ACTION_CANCEL;
if (upOrCancel && !mExpandedVisible) {
setInteracting(StatusBarManager.WINDOW_STATUS_BAR, false);
} else {
setInteracting(StatusBarManager.WINDOW_STATUS_BAR, true);
}
}
return false;
}从这里可以看出，最后return的是false，而其中执行的一个比较重要的方法是setInteracting()，它的作用隐藏和显示状态栏拓展出来的部分就是下拉菜单这块，不是很难理解，我们在着重分析下panelBar的onTouchEvent()方法，
@Override
public boolean onTouchEvent(MotionEvent event) {
// Allow subclasses to implement enable/disable semantics
if (!panelsEnabled()) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
Log.v(TAG, String.format("onTouch: all panels disabled, ignoring touch at (%d,%d)",
(int) event.getX(), (int) event.getY()));
}
return false;
}
// figure out which panel needs to be talked to here
if (event.getAction() == MotionEvent.ACTION_DOWN) {
final PanelView panel = selectPanelForTouch(event);
if (panel == null) {
// panel is not there, so we'll eat the gesture
Log.v(TAG, String.format("onTouch: no panel for touch at (%d,%d)",
(int) event.getX(), (int) event.getY()));
mTouchingPanel = null;
return true;
}
boolean enabled = panel.isEnabled();
if (DEBUG) LOG("PanelBar.onTouch: state=%d ACTION_DOWN: panel %s %s", mState, panel,
(enabled ? "" : " (disabled)"));
if (!enabled) {
// panel is disabled, so we'll eat the gesture
Log.v(TAG, String.format(
"onTouch: panel (%s) is disabled, ignoring touch at (%d,%d)",
panel, (int) event.getX(), (int) event.getY()));
mTouchingPanel = null;
return true;
}
startOpeningPanel(panel);
}
final boolean result = mTouchingPanel != null
? mTouchingPanel.onTouchEvent(event)
: true;
return result;
}一般的下拉菜单有两种，一种是SettingPanelView还有种 NotificationPanelView， panelBar的onTouchEvent主要寻找哪块PanelView消费了这个MotionEvent，所以，我们继续跟踪PanelView的onTouchEvent，
@Override
public boolean onTouchEvent(MotionEvent event) {
if (mInstantExpanding || mTouchDisabled
|| (mMotionAborted && event.getActionMasked() != MotionEvent.ACTION_DOWN)) {
return false;
}
/*
* We capture touch events here and update the expand height here in case according to
* the users fingers. This also handles multi-touch.
*
* If the user just clicks shortly, we give him a quick peek of the shade.
*
* Flinging is also enabled in order to open or close the shade.
*/
int pointerIndex = event.findPointerIndex(mTrackingPointer);
if (pointerIndex < 0) {
pointerIndex = 0;
mTrackingPointer = event.getPointerId(pointerIndex);
}
final float x = event.getX(pointerIndex);
final float y = event.getY(pointerIndex);
if (event.getActionMasked() == MotionEvent.ACTION_DOWN) {
mGestureWaitForTouchSlop = isFullyCollapsed() || hasConflictingGestures();
mIgnoreXTouchSlop = isFullyCollapsed() || shouldGestureIgnoreXTouchSlop(x, y);
}
switch (event.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
startExpandMotion(x, y, false /* startTracking */, mExpandedHeight);
mJustPeeked = false;
mPanelClosedOnDown = isFullyCollapsed();
mHasLayoutedSinceDown = false;
mUpdateFlingOnLayout = false;
mMotionAborted = false;
mPeekTouching = mPanelClosedOnDown;
mTouchAboveFalsingThreshold = false;
mCollapsedAndHeadsUpOnDown = isFullyCollapsed()
&& mHeadsUpManager.hasPinnedHeadsUp();
if (mVelocityTracker == null) {
initVelocityTracker();
}
trackMovement(event);
if (!mGestureWaitForTouchSlop || (mHeightAnimator != null && !mHintAnimationRunning) ||
mPeekPending || mPeekAnimator != null) {
cancelHeightAnimator();
cancelPeek();
mTouchSlopExceeded = (mHeightAnimator != null && !mHintAnimationRunning)
|| mPeekPending || mPeekAnimator != null;
onTrackingStarted();
}
if (isFullyCollapsed() && !mHeadsUpManager.hasPinnedHeadsUp()) {
schedulePeek();
}
break;
case MotionEvent.ACTION_POINTER_UP:
final int upPointer = event.getPointerId(event.getActionIndex());
if (mTrackingPointer == upPointer) {
// gesture is ongoing, find a new pointer to track
final int newIndex = event.getPointerId(0) != upPointer ? 0 : 1;
final float newY = event.getY(newIndex);
final float newX = event.getX(newIndex);
mTrackingPointer = event.getPointerId(newIndex);
startExpandMotion(newX, newY, true /* startTracking */, mExpandedHeight);
}
break;
case MotionEvent.ACTION_POINTER_DOWN:
if (mStatusBar.getBarState() == StatusBarState.KEYGUARD) {
mMotionAborted = true;
endMotionEvent(event, x, y, true /* forceCancel */);
return false;
}
break;
case MotionEvent.ACTION_MOVE:
float h = y - mInitialTouchY;
// If the panel was collapsed when touching, we only need to check for the
// y-component of the gesture, as we have no conflicting horizontal gesture.
if (Math.abs(h) > mTouchSlop
&& (Math.abs(h) > Math.abs(x - mInitialTouchX)
|| mIgnoreXTouchSlop)) {
mTouchSlopExceeded = true;
if (mGestureWaitForTouchSlop && !mTracking && !mCollapsedAndHeadsUpOnDown) {
if (!mJustPeeked && mInitialOffsetOnTouch != 0f) {
startExpandMotion(x, y, false /* startTracking */, mExpandedHeight);
h = 0;
}
cancelHeightAnimator();
removeCallbacks(mPeekRunnable);
mPeekPending = false;
onTrackingStarted();
}
}
final float newHeight = Math.max(0, h + mInitialOffsetOnTouch);
if (newHeight > mPeekHeight) {
if (mPeekAnimator != null) {
mPeekAnimator.cancel();
}
mJustPeeked = false;
}
if (-h >= getFalsingThreshold()) {
mTouchAboveFalsingThreshold = true;
mUpwardsWhenTresholdReached = isDirectionUpwards(x, y);
}
if (!mJustPeeked && (!mGestureWaitForTouchSlop || mTracking) && !isTrackingBlocked()) {
setExpandedHeightInternal(newHeight);
}
trackMovement(event);
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
trackMovement(event);
endMotionEvent(event, x, y, false /* forceCancel */);
break;
}
return !mGestureWaitForTouchSlop || mTracking;
}PanelView的onTouchEvent()方法主要对手势的处理逻辑比较多，但是也是很常规的对自定义View的处理，和下拉刷新控件逻辑和用到的技术都差不多的东西，手一直下拉过程中，不断的刷新，重绘控件，如果在中途放手，那么会根据你放手的位置来决定到底是关闭or打开panelView。
动态更改状态栏高度
像一般的定制SystemUI，静态的修改状态栏高度是经常都会碰到的，我们会去修改frameworks/base/core/res/res/values/dimens.xml中的值，
<dimen name="toast_y_offset">64dip</dimen>
<!-- Height of the status bar -->
<dimen name="status_bar_height">24dp</dimen>
<!-- Height of the bottom navigation / system bar. -->
<dimen name="navigation_bar_height">48dp</dimen>然后将framework-res.jar push到/system/framework/底下重启机器就可以生效了，但是如何动态的修改状态的高度呢，我们知道在Android源码中，Window这个类非常的抽象，它会在Activity启动的时候附着在Activity中，然后承担着试图显示的职责，而PhoneWindow是Window的唯一实现类，PhoneWindowManager可以说是一个策略类，它实现了WindowManagerPolicy，从名字也可以看出，主要是处理一些和视图相关的逻辑部分，当然了整个Android的任何一个模块都是相当的复杂，我们这里并不去深究，我们知道PhoneWindowManager这个类做了很多初始化工作，包括从framework/res中获取状态栏的高度值
mStatusBarHeight =
res.getDimensionPixelSize(com.android.internal.R.dimen.status_bar_height);然后PhoneWindowManager还要确定绘制的各个区域，然后进行测量，绘制的工作，所以我们只要动态的设置PhoneWindowManager中的mStatusBarHeight，然后在重新绘制系统的视图即可。具体的，我们该如何动态修改mStatusBarHeight的值，我们的好好的分析PhoneWindowManager这个类了，可以看到
...
IStatusBarService mStatusBarService;
...在PhoneWindowManager这个类中有mStatusBarService这个属性，这就意味着我们可以在这里直接操作SystemUI，StatusBarManagerService同样也实现了这个接口，而StatusBarManagerService内部有IStatusBar这个代理类，同样，SystemUI中CommandQueue也实现了IStatusBar（上文提到，这里SystemUI相当于服务端），这样在PhoneWindowManager就可以直接控制SystemUI的行为，那么我们怎么样能够修改PhoneWindowManager中的状态栏高度值呢，我们看到PhoneWindowManager实现了WindowPolicy接口，而在WindowManagerService是持有WindowPolicy这个引用的。
...
final WindowManagerPolicy mPolicy = new PhoneWindowManager();
...这样，我们只需要能够调用WindowManagerService里面的方法，就能直接控制PhoneWindowManager，从而控制SystemUI了，再看看我们的WindowManagerService是继承了IWindowManager.Stub这个通信借口，所以，所有问题都解决了，我们只需要在IWindowManager.aidl文件中，添加updateStatusBarHeight()方法，然后在之前我们提到的所有地方都添加方法实现，最终就会调用到PhoneWindowManager，修改状态栏的高度值，当SystemUI接受到回调之后，调用WindowManager的updateLayoutView()方法，就会重新绘制我们的系统UI。
上图是整个调用流程，这样就可以动态的修改我们的状态栏高度了。