Android線性佈局背景透明度

我想更改我的Android LinearLayout背景透明度。在這裏我試圖改變activity_view_full_screen_image.xml中的android：alpha =「0.4」值。但是佈局內容（如PhotoView透明度）會改變，而不是佈局透明度。請快速解答此問題，敬請諒解。Android線性佈局背景透明度

這裏是我的代碼：

ViewFullScreenImage.java

import android.graphics.Color; 
import android.net.Uri; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.widget.LinearLayout; 

import com.github.chrisbanes.photoview.PhotoView; 
import com.squareup.picasso.Picasso; 

import java.io.InputStream; 

public class ViewFullScreenImage extends AppCompatActivity { 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_view_full_screen_image); 
     loadImage(); 
    } 

    public void loadImage(){ 

     Uri imageUrl = Uri.parse("http://www.ucdmc.ucdavis.edu/hr/images/body/Health-Welness-Businesses.jpg"); 

     PhotoView photoView = (PhotoView) findViewById(R.id.photo_view); 
     Picasso.with(this).load(imageUrl).into(photoView); 
    } 
}

和

activity_full_screen_image.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/activity_view_full_screen_image" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:alpha="0.4" 
    tools:context="com.example.theace.fullscreen.ViewFullScreenImage"> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:id="@+id/my_layout" 
     android:orientation="vertical" 
     > 

     <com.github.chrisbanes.photoview.PhotoView 
      android:id="@+id/photo_view" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent"/> 


    </LinearLayout> 



</LinearLayout>

來源

2017-08-16 Nuwan Withanage