问题
I'm trying to add a message in a web view, the message should come out when you do not have an Internet connection.
I have tried many ways but I always make a mistake that I do not understand.
I create a folder called "assets" and add a file "error.html" following a YouTube tutorial but it gives me errors
I will write my codes here without what I saw on YouTube.
Thank you
MainActivity.java
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.widget.SwipeRefreshLayout;
import android.view.KeyEvent;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.ProgressBar;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, SwipeRefreshLayout.OnRefreshListener {
private WebView wv;
private SwipeRefreshLayout sr;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
navigationView.setItemIconTintList(null);
sr = (SwipeRefreshLayout) findViewById(R.id.sr);
sr.setOnRefreshListener(this);
wv=(WebView)findViewById(R.id.wv);
WebSettings webSettings=wv.getSettings();
webSettings.setJavaScriptEnabled(true);
wv.loadUrl("//MyURL//");
wv.setWebViewClient(new WebViewClient());
wv.setWebViewClient(new CustomWebViewClient());
}
private class CustomWebViewClient extends WebViewClient {
@Override
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if(url.contains("//MyURL//")) {
view.loadUrl(url);
} else {
Intent i = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
startActivity(i);
}
return true;
}
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return false;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.Inicio) {
wv.loadUrl("//social//");
} else if (id == R.id.Insta) {
wv.loadUrl("//social//");
} else if (id == R.id.Facebook) {
wv.loadUrl("//social//");
} else if (id == R.id.Twitter) {
wv.loadUrl("//social//");
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
@Override
public void onRefresh() {
wv.reload();
sr.setRefreshing(false);
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && wv.canGoBack()) {
//if Back key pressed and webview can navigate to previous page
wv.goBack();
// go back to previous page
return true;
}
else
{
finish();
// finish the activity
}
return super.onKeyDown(keyCode, event);
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
int action = event.getAction();
int keyCode = event.getKeyCode();
switch (keyCode) {
case KeyEvent.KEYCODE_VOLUME_UP:
if (action == KeyEvent.ACTION_UP) {
// TODO
}
return false;
case KeyEvent.KEYCODE_VOLUME_DOWN:
if (action == KeyEvent.ACTION_DOWN) {
//TODO
}
return false;
default:
return super.dispatchKeyEvent(event);
}
}
}
Content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context=".MainActivity"
tools:showIn="@layout/app_bar_main">
<android.support.v4.widget.SwipeRefreshLayout
android:id="@+id/sr"
android:layout_width="match_parent"
android:layout_height="match_parent">
<WebView
android:id="@+id/wv"
android:layout_width="match_parent"
android:layout_height="match_parent">
</WebView>
</android.support.v4.widget.SwipeRefreshLayout>
</LinearLayout>
Thank You
回答1:
1) Create DetectConnection.java Class to check internet is available or not.
import android.content.Context;
import android.net.ConnectivityManager;
public class DetectConnection {
public static boolean checkInternetConnection(Context context) {
ConnectivityManager con_manager = (ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE);
return (con_manager.getActiveNetworkInfo() != null
&& con_manager.getActiveNetworkInfo().isAvailable()
&& con_manager.getActiveNetworkInfo().isConnected());
}
}
2) Change your code of onCreate method, before loading check whether internet is available or not,
wv = (WebView) findViewById(R.id.wv);
CustomWebViewClient c = new CustomWebViewClient();
wv.setWebViewClient(c);
wv.clearCache(true);
wv.clearHistory();
wv.getSettings().setJavaScriptEnabled(true);
wv.getSettings().setJavaScriptCanOpenWindowsAutomatically(true);
wv.getSettings().setBuiltInZoomControls(true);
if (!DetectConnection.checkInternetConnection(this)) {
wv.loadUrl("file:///android_asset/error.html"); //Change path if it is not correct
} else {
wv.loadUrl("http://www.google.com");
}
3) Change code of CustomWebViewClient. It is a class where you can get a callback for each URL. In that callback, Once a page finish loading you can check it.
// Function to load all URLs in same webview
private class CustomWebViewClient extends WebViewClient {
public boolean shouldOverrideUrlLoading(WebView view, String url) {
if(url.contains("//MyURL//")) {
view.loadUrl(url);
} else {
Intent i = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
startActivity(i);
}
return true;
}
@Override
public void onLoadResource(WebView view, String url){
if (!DetectConnection.checkInternetConnection(MainActivity.this)) {
wv.loadUrl("file:///android_asset/error.html"); //Change path if it is not correct
}
}
}
4) Add ACCESS_NETWORK_STATE Permission in AndroidMenifest.xml.
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
来源：https://stackoverflow.com/questions/55437061/how-to-show-no-internet-connection-dialog-in-webview-android-studio