I would like to put a Network Detector in an Android application, to inform a Screen immediately the Network state even if that state is changing. I have study similar questions in: Android: Internet connectivity change listener
So my Java code in Main Activity is:
package com.example.netdetector;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.Network;
import android.net.NetworkCapabilities;
import android.net.NetworkInfo;
import android.net.NetworkRequest;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.*;
public class MainActivity extends AppCompatActivity {
private TextView Screen;
@RequiresApi(api = Build.VERSION_CODES.M)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Screen = (TextView) findViewById(R.id.Screen);
Screen.setText("Start!");
ConnectivityManager.NetworkCallback networkCallback = new ConnectivityManager.NetworkCallback() {
@Override
public void onAvailable(Network network) {
// network available
Screen.setText("Net On!");
}
@Override
public void onLost(Network network) {
// network unavailable
Screen.setText("Net Off!");
}
};
ConnectivityManager connectivityManager =
(ConnectivityManager) this.getSystemService(Context.CONNECTIVITY_SERVICE);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
connectivityManager.registerDefaultNetworkCallback(networkCallback);
} else {
NetworkRequest request = new NetworkRequest.Builder()
.addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET).build();
connectivityManager.registerNetworkCallback(request, networkCallback);
}
}
}
The AndroidManifest.xml is:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.netdetector">
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<application
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.NetDetector">
<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>
The Layout activity_main.xml is:
<?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"
tools:context=".MainActivity">
<TextView
android:id="@+id/Screen"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:text="Hello World!"
android:textSize="25sp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.222" />
</androidx.constraintlayout.widget.ConstraintLayout>
There are some issues:
- Starting the App with the Network Off, the Screen displays "Start!" instead of "Net Off!"
- Starting the App with the Network On, the Screen displays "Net On" that is fine
- On changing Internet state while the app is running the Screen displays the right text for a few moments and the app closes immediately.
How can I fix 1 and 3? What went wrong?
Thanks Nickolas