Android设置theme中可能遇到的坑

<style name="AppTheme.NoActionBar">
  <item name="android:windowActionBar">false</item>
  <item name="android:windowNoTitle">true</item>
  <item name="android:windowDrawsSystemBarBackgrounds">true</item>
  <item name="android:statusBarColor">@android:color/transparent</item>
 </style>

<style name="AppTheme.NoActionBar">
  <item name="windowActionBar">false</item>
  <item name="windowNoTitle">true</item>
  <item name="android:windowDrawsSystemBarBackgrounds">true</item>
  <item name="android:statusBarColor">@android:color/transparent</item>
 </style>

<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>

public void setSupportActionBar(@Nullable Toolbar toolbar) {
  getDelegate().setSupportActionBar(toolbar);
 }

public void setSupportActionBar(Toolbar toolbar) {
  if (!(mOriginalWindowCallback instanceof Activity)) {
   // Only Activities support custom Action Bars
   return;
  }
  //这里会去判有没有actionbar存在，如果有直接抛异常
  final ActionBar ab = getSupportActionBar();
  if (ab instanceof WindowDecorActionBar) {
   throw new IllegalStateException("This Activity already has an action bar supplied " +
     "by the window decor. Do not request Window.FEATURE_SUPPORT_ACTION_BAR and set " +
     "windowActionBar to false in your theme to use a Toolbar instead.");
  }

  // If we reach here then we're setting a new action bar
  // First clear out the MenuInflater to make sure that it is valid for the new Action Bar
  mMenuInflater = null;

  // If we have an action bar currently, destroy it
  if (ab != null) {
   ab.onDestroy();
  }

  if (toolbar != null) {
   final ToolbarActionBar tbab = new ToolbarActionBar(toolbar,
     ((Activity) mContext).getTitle(), mAppCompatWindowCallback);
   mActionBar = tbab;
   mWindow.setCallback(tbab.getWrappedWindowCallback());
  } else {
   mActionBar = null;
   // Re-set the original window callback since we may have already set a Toolbar wrapper
   mWindow.setCallback(mAppCompatWindowCallback);
  }
  invalidateOptionsMenu();
 }

//这里会去判有没有actionbar存在，如果有直接抛异常
final ActionBar ab = getSupportActionBar();
  if (ab instanceof WindowDecorActionBar) {
   throw new IllegalStateException("This Activity already has an action bar supplied " +
     "by the window decor. Do not request Window.FEATURE_SUPPORT_ACTION_BAR and set " +
     "windowActionBar to false in your theme to use a Toolbar instead.");
  }