Android 透過網路抓圖秀在螢幕上

先修改 app/src/main/AndroidManifest.xml 檔案內容:

 <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.urlopen">
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        android:networkSecurityConfig="@xml/network_security"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.UrlOpen">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

在 res 目錄底下新建一個 xml 目錄( app/src/main/res/xml), 裏面放入 netwirk_security.xml 檔案內容, 以便信認所屬網域 192.168.0.1:

 <?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">192.168.0.1</domain>
    </domain-config>
</network-security-config

修改 app/src/main/res/layout/activity_main.xml, 加入 android:id="@+id/...",  檔案內容:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/mainLayout"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/sample_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

主程式 app/src/main/java/com/example/urlopen/MainActivity.kt  檔案內容:

package com.example.urlopen
import android.graphics.BitmapFactory
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.util.Log
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.constraintlayout.widget.ConstraintLayout
import java.net.URL
import java.util.concurrent.Executors
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val mainContext = this
        (findViewById(R.id.mainLayout) as ConstraintLayout) ?.apply {
            val imageView = ImageView(mainContext).apply {
                setLayoutParams(
                    ConstraintLayout.LayoutParams(
                            ViewGroup.LayoutParams.MATCH_PARENT,
                            ViewGroup.LayoutParams.WRAP_CONTENT
                    )
                )
            }
            addView(imageView)
            val url = "http://192.168.0.1/snap.jpg"
            val handler = Handler(Looper.getMainLooper())
            val getJPG = object : Runnable {
                override fun run() {
                  Executors.newSingleThreadExecutor() ?.execute {// doInBackground
                    try {
                        val stream = URL(url).openStream()
                        val jpg = BitmapFactory.decodeStream(stream)
                        handler.post { // onPostExecute
                            imageView.setImageBitmap(jpg)                          
                        }
                    } catch (e: Exception) {
                        Log.e("JNI", "network get fail!")
                    }
                  }
                }
            }
            getJPG.run()
        }
        //...
    }
}