Android GridLayout: layout_rowWeight not dividing item width equally

I'm using GridLayout for my items, I have 4 * 2 items in total.
I use layout_rowWeight="1" and layout_columnWeight="1" for each item.
However, the item are not divided equally. The first three item are large while the last item is small like this:

Here is my layout xml:

<GridLayout
    android:rowCount="2"
    android:columnCount="4"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:id="@+id/qrcode_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="21dp"
            android:layout_height="21dp"
            android:src="@drawable/ic_qrcode" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="12dp"
            android:text="@string/qrcode_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/grade_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="20dp"
            android:layout_height="23dp"
            android:src="@drawable/ic_grade" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="11dp"
            android:text="@string/grade_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/study_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="19dp"
            android:layout_height="24dp"
            android:src="@drawable/ic_study" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="11dp"
            android:text="@string/study_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/map_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="20dp"
            android:layout_height="20dp"
            android:src="@drawable/ic_map" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="12dp"
            android:text="@string/map_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/calendar_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="22dp"
            android:layout_height="22dp"
            android:src="@drawable/ic_calendar" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="11dp"
            android:text="@string/calendar_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/network_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="28dp"
            android:layout_height="21dp"
            android:src="@drawable/ic_internet" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="12dp"
            android:text="@string/network_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/contact_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="23dp"
            android:layout_height="20dp"
            android:src="@drawable/ic_contact" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="13dp"
            android:text="@string/contact_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/more_item"
        android:orientation="vertical"
        android:gravity="center"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1">

        <ImageView
            android:layout_width="20dp"
            android:layout_height="20dp"
            android:src="@drawable/ic_more" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="12dp"
            android:text="@string/more_item"
            android:textColor="#363636"
            android:textSize="12sp" />

    </LinearLayout>

</GridLayout>

It happens since you didn't specify width and height attributes for your wrapper LinearLayouts.

If you use layout_rowWeight and/or layout_columnWeight, you should also use layout_width and layout_height attributes for an even distribution of rows and columns.

Try adding these lines to each of your LinearLayouts:

android:layout_width="0dp"
android:layout_height="0dp"

After adding these lines, rows and columns will be evenly distributed according to GridLayout's width and height.