LinearLayout中将按钮右对齐遇到的问题

今天在做登陆界面时，为了达到以下效果



先将右边按钮设置成

android:layout_gravity="right"

后又做其他设置，右边按钮还是无法右边对齐，后做如下改动后方才实现，

将右边按钮放到另外一个LinearLayout中，并设置该LinearLayout的 android:gravity="right"，

这个布局代码如下

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
<include layout="@layout/title_firstpage"/>
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >

<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@drawable/img_bg_hua"
android:paddingTop="@dimen/margin_30"
android:paddingLeft="@dimen/margin_30"
android:paddingRight="@dimen/margin_30"
android:orientation="vertical"
>
<EditText
android:id="@id/loginname"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textEmailAddress|phone"
android:hint="@string/hint_login_loginname"
android:background="@drawable/img_bg_ring_top_n"
android:drawableLeft="@drawable/img_drawbleleft_mobile"
android:paddingLeft="@dimen/margin_15"
android:drawablePadding="@dimen/margin_15"
/>
<EditText
android:id="@id/password"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="textPassword"
android:hint="@string/hint_login_password"
android:background="@drawable/img_bg_ring_bottom_n"
android:drawableLeft="@drawable/img_drawbleleft_password"
android:paddingLeft="@dimen/margin_15"
android:drawablePadding="@dimen/margin_15"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:paddingTop="@dimen/margin_30"
>
<Button
android:id="@id/forget_password"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="left"
android:gravity="center"
android:background="@drawable/bg_button_login"
android:text="@string/forgetpassword"
android:textColor="@color/gray8F"
android:textSize="@dimen/textsize_7"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="right"
>
<Button
android:id="@id/login"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:background="@drawable/bg_button_login"
android:text="@string/login"
android:textColor="@color/red"
android:textSize="@dimen/textsize_7"
/>
</LinearLayout>

</LinearLayout>
</LinearLayout>
<!-- 标题栏投影 -->
<ImageView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@drawable/img_shadow_title"
tools:ignore="ContentDescription" />
</FrameLayout>
</LinearLayout>

不用LinearLayout，用RelativeLayout布局也可以实现，核心布局如下

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="@dimen/margin_50"
android:paddingRight="@dimen/margin_50"
android:paddingTop="@dimen/margin_30" >

<EditText
android:id="@id/loginname"
style="@style/edittext_login"
android:background="@drawable/img_bg_ring_top_n"
android:drawableLeft="@drawable/img_drawbleleft_mobile"
android:hint="@string/hint_login_loginname" />

<EditText
android:id="@id/password"
style="@style/edittext_login"
android:layout_below="@id/loginname"
android:background="@drawable/img_bg_ring_bottom_n"
android:drawableLeft="@drawable/img_drawbleleft_password"
android:hint="@string/hint_login_password"
android:inputType="textPassword" />

<Button
android:id="@id/forget_password"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/password"
android:layout_marginTop="@dimen/margin_35"
android:background="@drawable/bg_button_login"
android:text="@string/forgetpassword"
android:textColor="@color/gray8F"
android:textSize="@dimen/textsize_7" />

<Button
android:id="@id/login"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_below="@id/password"
android:layout_marginTop="@dimen/margin_35"
android:background="@drawable/bg_button_login"
android:text="@string/login"
android:textColor="@color/red"
android:textSize="@dimen/textsize_7" />

</RelativeLayout>