Come centrare il contenuto all'interno di un layout lineare?

Question

Sto cercando di centrare uno ImageView all'interno di uno LinearLayout in senso orizzontale e verticale, ma non riesco proprio a farlo. Il motivo principale per cui non sto utilizzando uno RelativeLayout è perché ho bisogno dello layout_weight (il mio Activity consiste di quattro colonne che dovrebbero essere equamente divise, e anche responsive a diverse larghezze dello schermo, ogni colonna avendo un ImageView centrato e non stirato) .

Ecco il mio xml finora:

<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:background="#000" 
    android:baselineAligned="false" 
    android:gravity="center" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context=".Main" > 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_speak" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_speak" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_readtext" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_readtext" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_edit" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_edit" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_config" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_config" /> 
    </LinearLayout> 
</LinearLayout> 

Answer 1

android:gravity gestisce l'allineamento della sua bambini,

android:layout_gravity gestisce l'allineamento di se stesso.

Quindi utilizzare uno di questi.

<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:background="#000" 
    android:baselineAligned="false" 
    android:gravity="center" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context=".Main" > 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:gravity="center" > 

     <ImageView 
      android:id="@+id/imageButton_speak" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_speak" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:gravity="center" > 

     <ImageView 
      android:id="@+id/imageButton_readtext" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_readtext" /> 
    </LinearLayout> 

    ... 
</LinearLayout> 

o

<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:background="#000" 
    android:baselineAligned="false" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context=".Main" > 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_speak" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="center" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_speak" /> 
    </LinearLayout> 

    <LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center" 
     android:layout_weight="1" > 

     <ImageView 
      android:id="@+id/imageButton_readtext" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="center" 
      android:background="@drawable/image_bg" 
      android:src="@drawable/ic_readtext" /> 
    </LinearLayout> 

    ... 
</LinearLayout> 

Answer 2

android:layout_gravity is used for itSelf of layout 

uso android:gravity="center" per bambino della vostra LinearLayout

in modo che il codice dovrebbe essere

<LinearLayout 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:gravity="center" 
     android:layout_weight="1" > 

Answer 3

ho provato le soluzioni qui, ma ho problema e provare alcune modifiche mi dispiaccia il male in layout_width necessario wrap_content come questo

<LinearLayout 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:gravity="center" 
    android:layout_weight="1" >