Android6.0 旋轉屏幕（四）應用強制設置方向

有時候我們也可以強制應用橫頻，這又是如何做到的？

就是調用了AMS的setRequestedOrientation接口，這個接口先是調用WMS的setAppOrientation函數設置這個Activity在WMS中的方向。然後在調用WMS的updateOrientationFromAppTokens函數旋轉屏幕，最後在調用updateConfigurationLocked這個函數之前博客分析過就是是否讓Activity重新Launch等。

    @Override
    public void setRequestedOrientation(IBinder token, int requestedOrientation) {
        synchronized (this) {
            ActivityRecord r = ActivityRecord.isInStackLocked(token);
            if (r == null) {
                return;
            }
            if (r.task != null && r.task.mResizeable) {
                // Fixed screen orientation isn't supported with resizeable activities.
                return;
            }
            final long origId = Binder.clearCallingIdentity();
            mWindowManager.setAppOrientation(r.appToken, requestedOrientation);
            Configuration config = mWindowManager.updateOrientationFromAppTokens(
                    mConfiguration, r.mayFreezeScreenLocked(r.app) ? r.appToken : null);
            if (config != null) {
                r.frozenBeforeDestroy = true;
                if (!updateConfigurationLocked(config, r, false, false)) {
                    mStackSupervisor.resumeTopActivitiesLocked();
                }
            }
            Binder.restoreCallingIdentity(origId);
        }
    }

我們先看下WMS的setAppOrientation函數，很簡單就是找到這個apptoken的APPWindowToken，然後將其requestedOrientation值賦值。

    @Override
    public void setAppOrientation(IApplicationToken token, int requestedOrientation) {
        if (!checkCallingPermission(android.Manifest.permission.MANAGE_APP_TOKENS,
                "setAppOrientation()")) {
            throw new SecurityException("Requires MANAGE_APP_TOKENS permission");
        }
 
        synchronized(mWindowMap) {
            AppWindowToken atoken = findAppWindowToken(token.asBinder());
            if (atoken == null) {
                Slog.w(TAG, "Attempted to set orientation of non-existing app token: " + token);
                return;
            }
 
            atoken.requestedOrientation = requestedOrientation;
        }
    }

然後我們再來看WMS的updateOrientationFromAppTokens函數，這個函數主要調用了updateOrientationFromAppTokensLocked函數，這個函數先調用另一個updateOrientationFromAppTokensLocked函數，根據這個函數的返回值，返回true代表要旋轉，就調用computeNewConfigurationLocked計算Configuration返回。

    private Configuration updateOrientationFromAppTokensLocked(
            Configuration currentConfig, IBinder freezeThisOneIfNeeded) {
        if (!mDisplayReady) {
            return null;
        }
        Configuration config = null;
 
        if (updateOrientationFromAppTokensLocked(false)) {
            if (freezeThisOneIfNeeded != null) {
                AppWindowToken atoken = findAppWindowToken(freezeThisOneIfNeeded);
                if (atoken != null) {
                    startAppFreezingScreenLocked(atoken);
                }
            }
            config = computeNewConfigurationLocked();
 
        } else if (currentConfig != null) {
            // No obvious action we need to take, but if our current
            // state mismatches the activity manager's, update it,
            // disregarding font scale, which should remain set to
            // the value of the previous configuration.
            mTempConfiguration.setToDefaults();
            mTempConfiguration.fontScale = currentConfig.fontScale;
            computeScreenConfigurationLocked(mTempConfiguration);
            if (currentConfig.diff(mTempConfiguration) != 0) {
                mWaitingForConfig = true;
                final DisplayContent displayContent = getDefaultDisplayContentLocked();
                displayContent.layoutNeeded = true;
                int anim[] = new int[2];
                if (displayContent.isDimming()) {
                    anim[0] = anim[1] = 0;
                } else {
                    mPolicy.selectRotationAnimationLw(anim);
                }
                startFreezingDisplayLocked(false, anim[0], anim[1]);
                config = new Configuration(mTempConfiguration);
            }
        }
 
        return config;
    }

我們來看下updateOrientationFromAppTokensLocked函數，我們先調用了getOrientationLocked函數獲取上次強制設置的方向，如果不同就調用updateRotationUncheckedLocked函數，這個函數之前博客分析過了，流程就一樣了。最後就到DisplayManagerService中設置設備的方向。

    boolean updateOrientationFromAppTokensLocked(boolean inTransaction) {
        long ident = Binder.clearCallingIdentity();
        try {
            int req = getOrientationLocked();
            if (req != mForcedAppOrientation) {
                mForcedAppOrientation = req;
                //send a message to Policy indicating orientation change to take
                //action like disabling/enabling sensors etc.,
                mPolicy.setCurrentOrientationLw(req);
                if (updateRotationUncheckedLocked(inTransaction)) {
                    // changed
                    return true;
                }
            }
 
            return false;
        } finally {
            Binder.restoreCallingIdentity(ident);
        }
    }

最後我們回到AMS的setRequestedOrientation函數，我們調用updateConfigurationLocked函數，當返回false，就是現在的狀態要改變（比如重啓Activity），然後就調用ActivityStackSupervisor的resumeTopActivitiesLocked函數來啓動最上面的Activity。

    public void setRequestedOrientation(IBinder token, int requestedOrientation) {
        synchronized (this) {
            ActivityRecord r = ActivityRecord.isInStackLocked(token);
            if (r == null) {
                return;
            }
            if (r.task != null && r.task.mResizeable) {
                // Fixed screen orientation isn't supported with resizeable activities.
                return;
            }
            final long origId = Binder.clearCallingIdentity();
            mWindowManager.setAppOrientation(r.appToken, requestedOrientation);
            Configuration config = mWindowManager.updateOrientationFromAppTokens(
                    mConfiguration, r.mayFreezeScreenLocked(r.app) ? r.appToken : null);
            if (config != null) {
                r.frozenBeforeDestroy = true;
                if (!updateConfigurationLocked(config, r, false, false)) {
                    mStackSupervisor.resumeTopActivitiesLocked();
                }
            }
            Binder.restoreCallingIdentity(origId);
        }
    }