alertdialog/src/main/java/com/yanzhenjie/alertdialog/AlertDialog.java
public static Builder newBuilder(Context context, int themeResId) {
        if (Build.VERSION.SDK_INT >= 21) {
            return new APi21Builder(context, themeResId);
        }
        return new Api20Builder(context, themeResId);
    }
public static Builder newBuilder(Context context, int themeResId) {
        if (Build.VERSION.SDK_INT >= 21) {
            return new APi21Builder(context, themeResId);
        }
        return new Api20Builder(context, themeResId);
    }
Create new Builder.

@param context    context.
@param themeResId theme res id.
@return {@link Builder}.