在Android AMS(二) App啟動過程之onCreate中我們講了onCreate的呼叫流程，這篇我們接著分析onResume的流程

ActivityThread.java-->handleLaunchActivity()中呼叫performLaunchActivity()走到activity的onCreate，onStart狀態後，會呼叫handleResumeActivity()方法

final void handleResumeActivity(IBinder token,
            boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
        ActivityClientRecord r = mActivities.get(token);
        if (!checkAndUpdateLifecycleSeq(seq, r, "resumeActivity")) {
            return;
        }

        // If we are getting ready to gc after going to the background, well
        // we are back active so skip it.
        unscheduleGcIdler();
        mSomeActivitiesChanged = true;

        // TODO Push resumeArgs into the activity for consideration
        r = performResumeActivity(token, clearHide, reason);

        if (r != null) {
            final Activity a = r.activity;

            if (localLOGV) Slog.v(
                TAG, "Resume " + r + " started activity: " +
                a.mStartedActivity + ", hideForNow: " + r.hideForNow
                + ", finished: " + a.mFinished);

            final int forwardBit = isForward ?
                    WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;

            // If the window hasn't yet been added to the window manager,
            // and this guy didn't finish itself or start another activity,
            // then go ahead and add the window.
            boolean willBeVisible = !a.mStartedActivity;
            if (!willBeVisible) {
                try {
                    willBeVisible = ActivityManager.getService().willActivityBeVisible(
                            a.getActivityToken());
                } catch (RemoteException e) {
                    throw e.rethrowFromSystemServer();
                }
            }
            if (r.window == null && !a.mFinished && willBeVisible) {
                //getWindow就是Activity attach（）中new的PhoneWindow()
                r.window = r.activity.getWindow();
                View decor = r.window.getDecorView();
                decor.setVisibility(View.INVISIBLE);
                ViewManager wm = a.getWindowManager();
                WindowManager.LayoutParams l = r.window.getAttributes();
                a.mDecor = decor;
                l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
                l.softInputMode |= forwardBit;
                if (r.mPreserveWindow) {
                    // SPRD: Bug711794, ensure that the decor view is attached to window.
                    // if the remain decor view is not attached to window, we should make sure
                    // that it will been attached in the following workflow.
                    if(DecorView.isAddedToWindow(decor)) a.mWindowAdded = true;
                    r.mPreserveWindow = false;
                    // Normally the ViewRoot sets up callbacks with the Activity
                    // in addView->ViewRootImpl#setView. If we are instead reusing
                    // the decor view we have to notify the view root that the
                    // callbacks may have changed.
                    ViewRootImpl impl = decor.getViewRootImpl();
                    if (impl != null) {
                        // add systrace tag for bug 661753
                        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "notifyChildRebuilt");
                        impl.notifyChildRebuilt();
                        // add systrace tag for bug 661753
                        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                    }
                }
                if (a.mVisibleFromClient) {
                    if (!a.mWindowAdded) {
                        a.mWindowAdded = true;
                        // add systrace tag for bug 661753
                        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "addView");
                        wm.addView(decor, l);
                        // add systrace tag for bug 661753
                        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                        DecorView.setAddedToWindow(a.mDecor);
                    } else {
                        // The activity will get a callback for this {@link LayoutParams} change
                        // earlier. However, at that time the decor will not be set (this is set
                        // in this method), so no action will be taken. This call ensures the
                        // callback occurs with the decor set.
                        a.onWindowAttributesChanged(l);
                    }
                }

            // If the window has already been added, but during resume
            // we started another activity, then don't yet make the
            // window visible.
            } else if (!willBeVisible) {
                if (localLOGV) Slog.v(
                    TAG, "Launch " + r + " mStartedActivity set");
                r.hideForNow = true;
            }

            // add systrace tag for bug 661753
            Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "cleanUpPendingRemoveWindows");

            // Get rid of anything left hanging around.
            cleanUpPendingRemoveWindows(r, false /* force */);

            // add systrace tag for bug 661753
            Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

            // The window is now visible if it has been added, we are not
            // simply finishing, and we are not starting another activity.
            if (!r.activity.mFinished && willBeVisible
                    && r.activity.mDecor != null && !r.hideForNow) {
                if (r.newConfig != null) {
                    performConfigurationChangedForActivity(r, r.newConfig);
                    if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
                            + r.activityInfo.name + " with newConfig " + r.activity.mCurrentConfig);
                    r.newConfig = null;
                }
                if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
                        + isForward);
                WindowManager.LayoutParams l = r.window.getAttributes();
                if ((l.softInputMode
                        & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
                        != forwardBit) {
                    l.softInputMode = (l.softInputMode
                            & (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
                            | forwardBit;
                    if (r.activity.mVisibleFromClient) {
                        ViewManager wm = a.getWindowManager();
                        View decor = r.window.getDecorView();
                        // add systrace tag for bug 661753
                        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "updateViewLayout");
                        wm.updateViewLayout(decor, l);
                        // add systrace tag for bug 661753
                        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                    }
                }

                r.activity.mVisibleFromServer = true;
                mNumVisibleActivities++;
                if (r.activity.mVisibleFromClient) {
                    r.activity.makeVisible();
                }
            }

            if (!r.onlyLocalRequest) {
                r.nextIdle = mNewActivities;
                mNewActivities = r;
                if (localLOGV) Slog.v(
                    TAG, "Scheduling idle handler for " + r);
                Looper.myQueue().addIdleHandler(new Idler());
            }
            r.onlyLocalRequest = false;

            if (UsimNotifier.isNotifyEnabled(getApplication())) {
               UsimNotifier.getInstance().startNotify(r.activity);
            }

            // Tell the activity manager we have resumed.
            if (reallyResume) {
                try {
                    // add systrace tag for bug 661753
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityResumed");
                    ActivityManager.getService().activityResumed(token);
                } catch (RemoteException ex) {
                    throw ex.rethrowFromSystemServer();
                } finally {
                    // add systrace tag for bug 661753
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                }
            }

        } else {
            // If an exception was thrown when trying to resume, then
            // just end this activity.
            try {
                // add systrace tag for bug 661753
                Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "finishActivity");
                ActivityManager.getService()
                    .finishActivity(token, Activity.RESULT_CANCELED, null,
                            Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            } finally {
                // add systrace tag for bug 661753
                Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
            }
        }
    }
 

主要作用是呼叫performResumeActivity()到activity的onResume狀態，然後獲取DecorView，建立一個關聯的ViewRootImpl物件,用來配合WindowManagerService服務來管理該Activity元件的視窗狀態，最後addView

1.首先看下performResumeActivity()

    public final ActivityClientRecord performResumeActivity(IBinder token,
            boolean clearHide, String reason) {
        ActivityClientRecord r = mActivities.get(token);
        if (localLOGV) Slog.v(TAG, "Performing resume of " + r
                + " finished=" + r.activity.mFinished);
        if (r != null && !r.activity.mFinished) {
            if (clearHide) {
                r.hideForNow = false;
                r.activity.mStartedActivity = false;
            }
            try {
                r.activity.onStateNotSaved();
                r.activity.mFragments.noteStateNotSaved();
                checkAndBlockForNetworkAccess();
                if (r.pendingIntents != null) {
                    deliverNewIntents(r, r.pendingIntents);
                    r.pendingIntents = null;
                }
                if (r.pendingResults != null) {
                    deliverResults(r, r.pendingResults);
                    r.pendingResults = null;
                }
                // add systrace tag for bug 661753
                Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "performResume");
                r.activity.performResume();

                synchronized (mResourcesManager) {
                    // If there is a pending local relaunch that was requested when the activity was
                    // paused, it will put the activity into paused state when it finally happens.
                    // Since the activity resumed before being relaunched, we don't want that to
                    // happen, so we need to clear the request to relaunch paused.
                    for (int i = mRelaunchingActivities.size() - 1; i >= 0; i--) {
                        final ActivityClientRecord relaunching = mRelaunchingActivities.get(i);
                        if (relaunching.token == r.token
                                && relaunching.onlyLocalRequest && relaunching.startsNotResumed) {
                            relaunching.startsNotResumed = false;
                        }
                    }
                }

                EventLog.writeEvent(LOG_AM_ON_RESUME_CALLED, UserHandle.myUserId(),
                        r.activity.getComponentName().getClassName(), reason);

                r.paused = false;
                r.stopped = false;
                r.state = null;
                r.persistentState = null;
            } catch (Exception e) {
                if (!mInstrumentation.onException(r.activity, e)) {
                    throw new RuntimeException(
                        "Unable to resume activity "
                        + r.intent.getComponent().toShortString()
                        + ": " + e.toString(), e);
                }
            } finally {
                // add systrace tag for bug 661753
                Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
            }
        }
        return r;
    }
 

Activity.java-->performResume()

    final void performResume() {
        performRestart();

        mFragments.execPendingActions();

        mLastNonConfigurationInstances = null;

        mCalled = false;
        // mResumed is set by the instrumentation
        mInstrumentation.callActivityOnResume(this);
        if (!mCalled) {
            throw new SuperNotCalledException(
                "Activity " + mComponent.toShortString() +
                " did not call through to super.onResume()");
        }

        // invisible activities must be finished before onResume() completes
        if (!mVisibleFromClient && !mFinished) {
            Log.w(TAG, "An activity without a UI must call finish() before onResume() completes");
            if (getApplicationInfo().targetSdkVersion
                    > android.os.Build.VERSION_CODES.LOLLIPOP_MR1) {
                throw new IllegalStateException(
                        "Activity " + mComponent.toShortString() +
                        " did not call finish() prior to onResume() completing");
            }
        }

        // Now really resume, and install the current status bar and menu.
        mCalled = false;

        mFragments.dispatchResume();
        mFragments.execPendingActions();

        onPostResume();
        if (!mCalled) {
            throw new SuperNotCalledException(
                "Activity " + mComponent.toShortString() +
                " did not call through to super.onPostResume()");
      
 

Instrumentation.java-->callActivityOnResume()

    public void callActivityOnResume(Activity activity) {
        activity.mResumed = true;
        // add systrace tag for bug 661753
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activity.onResume");
        activity.onResume();
        // add systrace tag for bug 661753
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

        if (mActivityMonitors != null) {
            synchronized (mSync) {
                final int N = mActivityMonitors.size();
                for (int i=0; i<N; i++) {
                    final ActivityMonitor am = mActivityMonitors.get(i);
                    am.match(activity, activity, activity.getIntent());
                }
            }
        }
    }

Activity.java-->onResume()

    protected void onResume() {
        if (DEBUG_LIFECYCLE) Slog.v(TAG, "onResume " + this);
        getApplication().dispatchActivityResumed(this);
        mActivityTransitionState.onResume(this, isTopOfTask());
        mCalled = true;
    }

到這裡activity已經到了onResume的狀態，下面我們繼續ViewRootImpl建立的過程

2.ViewRootImpl建立流程

在 Android AMS(二) App啟動過程之onCreate我們知道在activity onCreate後，會呼叫Activity的attach（）方法new PhoneWindow

所以r.window = r.activity.getWindow();得到的就是PhoneWindow的例項

getDecorView()是Window.java的一個抽象方法，PhoneWindow繼承了這個Window

    @Override
    public final View getDecorView() {
        if (mDecor == null || mForceDecorInstall) {
            installDecor();
        }
        return mDecor;
    }

PhoneWindow.java-->installDecor()

    private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);
        ......
    }

PhoneWindow.java-->generateDecor()

    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().getResources());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

創建出DecorView之後，從DecorView中獲取ViewRootImpl

ViewRootImpl impl = decor.getViewRootImpl();

我們看下ViewRootImpl的構造方法

public ViewRootImpl(Context context, Display display) {
        mContext = context;
        mWindowSession = WindowManagerGlobal.getWindowSession();
        mDisplay = display;
        mBasePackageName = context.getBasePackageName();
        mThread = Thread.currentThread();
        mLocation = new WindowLeaked(null);
        mLocation.fillInStackTrace();
        mWidth = -1;
        mHeight = -1;
        mDirty = new Rect();
        mTempRect = new Rect();
        mVisRect = new Rect();
        mWinFrame = new Rect();
        mWindow = new W(this);
        mTargetSdkVersion = context.getApplicationInfo().targetSdkVersion;
        mViewVisibility = View.GONE;
        mTransparentRegion = new Region();
        mPreviousTransparentRegion = new Region();
        mFirst = true; // true for the first time the view is added
        mAdded = false;
        mAttachInfo = new View.AttachInfo(mWindowSession, mWindow, display, this, mHandler, this,
                context);
        mAccessibilityManager = AccessibilityManager.getInstance(context);
        mAccessibilityManager.addAccessibilityStateChangeListener(
                mAccessibilityInteractionConnectionManager, mHandler);
        mHighContrastTextManager = new HighContrastTextManager();
        mAccessibilityManager.addHighTextContrastStateChangeListener(
                mHighContrastTextManager, mHandler);
        mViewConfiguration = ViewConfiguration.get(context);
        mDensity = context.getResources().getDisplayMetrics().densityDpi;
        mNoncompatDensity = context.getResources().getDisplayMetrics().noncompatDensityDpi;
        mFallbackEventHandler = new PhoneFallbackEventHandler(context);
        mChoreographer = Choreographer.getInstance();
        mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);

        if (!sCompatibilityDone) {
            sAlwaysAssignFocus = true;

            sCompatibilityDone = true;
        }

        loadSystemProperties();
    }

在這裡獲取了WindowSession，W物件，這個以後我們在WMS學習中再研究

然後addView -->wm.addView(decor, l); 

這個wm是ViewManager，ViewManager是個介面，而WindowManager繼承了ViewManager，WindowManagerImpl實現了WindowManager

WindowManagerImpl.java-->addView()

    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
    }

WindowManagerGlobal.java-->addView()

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
        if (parentWindow != null) {
            parentWindow.adjustLayoutParamsForSubWindow(wparams);
        } else {
            // If there's no parent, then hardware acceleration for this view is
            // set from the application's hardware acceleration setting.
            final Context context = view.getContext();
            if (context != null
                    && (context.getApplicationInfo().flags
                            & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
                wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
            }
        }

        ViewRootImpl root;
        View panelParentView = null;

        synchronized (mLock) {
            // Start watching for system property changes.
            if (mSystemPropertyUpdater == null) {
                mSystemPropertyUpdater = new Runnable() {
                    @Override public void run() {
                        synchronized (mLock) {
                            for (int i = mRoots.size() - 1; i >= 0; --i) {
                                mRoots.get(i).loadSystemProperties();
                            }
                        }
                    }
                };
                SystemProperties.addChangeCallback(mSystemPropertyUpdater);
            }

            int index = findViewLocked(view, false);
            if (index >= 0) {
                if (mDyingViews.contains(view)) {
                    // Don't wait for MSG_DIE to make it's way through root's queue.
                    mRoots.get(index).doDie();
                } else {
                    throw new IllegalStateException("View " + view
                            + " has already been added to the window manager.");
                }
                // The previous removeView() had not completed executing. Now it has.
            }

            // If this is a panel window, then find the window it is being
            // attached to for future reference.
            if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                    wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
                final int count = mViews.size();
                for (int i = 0; i < count; i++) {
                    if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                        panelParentView = mViews.get(i);
                    }
                }
            }

            root = new SprdViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);

            // do this last because it fires off messages to start doing things
            try {
                root.setView(view, wparams, panelParentView);
            } catch (RuntimeException e) {
                // BadTokenException or InvalidDisplayException, clean up.
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
                throw e;
            }
        }
    }