获取屏幕高度的代码

int getScreenHeight(Activity context) {

WindowManager wm = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);

DisplayMetrics metrics = new DisplayMetrics();

wm.getDefaultDisplay().getMetrics(metrics);

return metrics.heightPixels;

}

问题现象

在Android N 7.0(SDK 24)上当，Activity进入过分屏模式再退出后，使用上面的代码去获取屏幕高度，得到的值是真正的屏幕高度减去状态栏的高度。然而在Android 7.1(SDK 25) 上，确没有这个问题，猜测是谷歌的BUG，在7.1上已经得到了修正。同时出问题的时候，传入的context是Activity，但是当我传入的是ApplicationContext时，返回的屏幕高度又是正确的，这就无语了。

问题原因

通过调试Android SDK 24和25的框架代码，发现出现问题的原因是，SDK 24的ActivityThread的performConfigurationChanged方法configuration没有正确地更新，但是SDK25做了修正。下面直接给出导致这个问题的框架代码：

Android 7.0

public final class ActivityThread {

...

private void performConfigurationChanged(...) {

...

boolean shouldChangeConfig = false;

if ((activity == null) || (activity.mCurrentConfig == null)) {

shouldChangeConfig = true;

} else {

// If the new config is the same as the config this Activity

// is already running with then don't bother calling

// onConfigurationChanged

int diff = activity.mCurrentConfig.diff(newConfig);

if (diff != 0) {

shouldChangeConfig = true;

}

}

...

}

Android 7.1

public final class ActivityThread {

...

private void performConfigurationChanged(...) {

...

boolean shouldChangeConfig = false;

if ((activity == null) || (activity.mCurrentConfig == null)) {

shouldChangeConfig = true;

} else {

// If the new config is the same as the config this Activity is already

// running with and the override config also didn't change, then don't

// bother calling onConfigurationChanged.

int diff = activity.mCurrentConfig.diff(newConfig);

if (diff != 0 || !mResourcesManager.isSameResourcesOverrideConfig(activityToken, amOverrideConfig)) {

// Always send the task-level config changes. For system-level configuration, if

// this activity doesn't handle any of the config changes, then don't bother

// calling onConfigurationChanged as we're going to destroy it.

if (!mUpdatingSystemConfig

|| (~activity.mActivityInfo.getRealConfigChanged() & diff) == 0

|| !reportToActivity) {

shouldChangeConfig = true;

}

}

}

...

}

比较这两块代码，可以发现 SDK25增加了!mResourcesManager.isSameResourcesOverrideConfig(activityToken, amOverrideConfig)这个条件来设置shouldChangeConfig的值。如果shouldChangeConfig那么Activity的configuration在退出分屏后会更新为未分屏之前的值。

解决方案

为了解决这个问题，只需要将context更换为ApplicationContext即可。