獲取屏幕高度的代碼

int getScreenHeight(Activity context) {
    WindowManager wm = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
    DisplayMetrics metrics = new DisplayMetrics();
    wm.getDefaultDisplay().getMetrics(metrics);
    return metrics.heightPixels;
} 

問題現(xiàn)象

在Android N 7.0（SDK 24）上當(dāng)，Activity進(jìn)入過分屏模式再退出后，使用上面的代碼去獲取屏幕高度，得到的值是真正的屏幕高度減去狀態(tài)欄的高度。然而在Android 7.1（SDK 25） 上，確沒有這個(gè)問題，猜測是谷歌的BUG，在7.1上已經(jīng)得到了修正。同時(shí)出問題的時(shí)候，傳入的context是Activity，但是當(dāng)我傳入的是ApplicationContext時(shí)，返回的屏幕高度又是正確的，這就無語了。

問題原因

通過調(diào)試Android SDK 24和25的框架代碼，發(fā)現(xiàn)出現(xiàn)問題的原因是，SDK 24的ActivityThread的performConfigurationChanged方法configuration沒有正確地更新，但是SDK25做了修正。下面直接給出導(dǎo)致這個(gè)問題的框架代碼：
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;
                }
            }
        }
        ...
}

比較這兩塊代碼，可以發(fā)現(xiàn) SDK25增加了!mResourcesManager.isSameResourcesOverrideConfig(activityToken, amOverrideConfig)這個(gè)條件來設(shè)置shouldChangeConfig的值。如果shouldChangeConfig那么Activity的configuration在退出分屏后會(huì)更新為未分屏之前的值。

解決方案

為了解決這個(gè)問題，只需要將context更換為ApplicationContext即可。