linearlayout问题

<?xml version="1.0" encoding="utf-8"?><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="match_parent"    android:background="@drawable/shape__present_tickets__container"    android:paddingBottom="@dimen/padding">    <TextView        android:id="@+id/title_text_view"        android:layout_width="match_parent"        android:layout_height="@dimen/title_bar__height"        android:background="@drawable/shape__dailylesson__title_bar"        android:gravity="center"        android:text="@string/present_tickets__title"        android:textColor="@color/txt_white"        android:textSize="@dimen/txt_h2"        android:textStyle="bold" />    <ImageView        android:id="@+id/teacher_image_view"        android:layout_width="80dp"        android:layout_height="80dp"        android:layout_below="@+id/title_text_view"        android:layout_centerHorizontal="true"        android:layout_marginTop="@dimen/margin"        tools:src="@drawable/ico_lesson_speaking" />    <TextView        android:id="@+id/ticket_info_text_view"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@+id/teacher_image_view"        android:gravity="center"        android:paddingLeft="@dimen/padding"        android:paddingRight="@dimen/padding"        android:paddingTop="@dimen/padding"        android:text="@string/present_tickets__ticket_info"        android:textColor="@color/txt_main"        android:textSize="@dimen/txt_medium"        android:textStyle="bold" />    <TextView        android:id="@+id/ticket_info_explanation_text_view"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@+id/ticket_info_text_view"        android:gravity="center"        android:paddingLeft="@dimen/padding"        android:paddingRight="@dimen/padding"        android:paddingTop="@dimen/padding"        android:text="@string/present_tickets__ticket_info_explanation"        android:textColor="@color/txt_main"        android:textSize="@dimen/txt_small" />    <Button        android:id="@+id/close_button"        style="@style/PrimaryButton"        android:layout_width="wrap_content"        android:layout_below="@+id/ticket_info_explanation_text_view"        android:layout_centerHorizontal="true"        android:layout_marginTop="@dimen/margin"        android:text="@string/present_tickets__close" /></RelativeLayout>

上面一段如果利用linearLayout改写就会挤在中间显示，而换成relativelayout就没有关系。

dialog的代码：

public Dialog onCreateDialog(Bundle savedInstanceState) {        final Dialog dialog = super.onCreateDialog(savedInstanceState);        dialog.getWindow().requestFeature(Window.FEATURE_NO_TITLE);        dialog.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN);        dialog.setContentView(R.layout.dialog_present_tickets);        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));        dialog.getWindow().getAttributes().windowAnimations = R.style.DialogAnimation;        teacherImageView = (ImageView) dialog.findViewById(R.id.teacher_image_view);        dialog.findViewById(R.id.close_button).findViewById(R.id.close_button).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                presenter.onClickClose();                dialog.dismiss();            }        });        presenter.onCreateDialog();        return dialog;    }