问无法将ImageButton垂直居中

EN

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#0e2a56"
    android:weightSum="100">
    <ImageButton
        android:src="@drawable/add"
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:layout_weight="25"
        android:id="@+id/imageButton1"
        android:gravity="center_vertical|center_horizontal"  />
    <TextView
        android:text="Add project"
        android:textColor="#FFFFFF"
        android:textSize="35dp"
        android:textStyle="bold"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:minWidth="25px"
        android:minHeight="25px"
        android:id="@+id/textView1"
        android:gravity="center_vertical|center_horizontal" />
</LinearLayout>