我在应用程序中使用WebView。这样，我在CanGoback()和goBack()函数中遇到错误。它说无法解析方法canGoBack ，这是我的WebView.java
public class Webview extends AppCompatActivity {
public String url;
private ProgressBar mProgressBar;
Webview myWebView;
@Override
protected void onCreate(Bundle savedInstanceState) {
final String url = getIntent().getStringExtra("URL");
// Request window feature action bar
requestWindowFeature(Window.FEATURE_ACTION_BAR);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_web_view);
final WebView myWebView = findViewById(R.id.webview);
myWebView.loadUrl(url);
WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
myWebView.getSettings().setBuiltInZoomControls(true);
myWebView.getSettings().setDefaultZoom(WebSettings.ZoomDensity.FAR);
myWebView.getSettings().setPluginState(WebSettings.PluginState.ON);
myWebView.getSettings().setAllowFileAccess(true);
// Get the widgets reference from XML layout
mProgressBar = findViewById(R.id.pb);
SwipeRefreshLayout mySwipeRefreshLayout=new SwipeRefreshLayout(this);
mySwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swiperefresh);
//code to check network availability
if(!isNetworkAvailable()){
//Create an alertdialog
AlertDialog.Builder Checkbuilder=new AlertDialog.Builder(Webview.this);
Checkbuilder.setIcon(R.drawable.error);
Checkbuilder.setTitle("Error!");
Checkbuilder.setMessage("Check Your Internet Connection.");
//Builder Retry Button
Checkbuilder.setPositiveButton("Retry", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int id) {
//Restart The Activity
Intent intent = getIntent();
finish();
startActivity(intent);
}
});
Checkbuilder.setNegativeButton("Exit", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
}) ;
AlertDialog alert=Checkbuilder.create();
alert.show();
}
//If internet is available load the url
else {
// Request to render the web page
if (savedInstanceState == null) {
myWebView.loadUrl(url);
}
}
Configuration config = getResources().getConfiguration();
final SwipeRefreshLayout finalMySwipeRefreshLayout1 = mySwipeRefreshLayout;
myWebView.setWebViewClient(new WebViewClient() {
@Override
public void onPageStarted(WebView view, String url, Bitmap favicon) {
// TODO Auto-generated method stub
super.onPageStarted(view, url, favicon);
// Visible the progressbar
mProgressBar.setVisibility(View.VISIBLE);
}
@Override
public void onPageFinished(WebView view, String url) {
finalMySwipeRefreshLayout1.setRefreshing(false);
}
});
//Code for handling download
myWebView.setDownloadListener(new DownloadListener() {
public void onDownloadStart(String url, String userAgent,
String contentDisposition, String mimetype,
long contentLength) {
DownloadManager.Request request = new DownloadManager.Request( Uri.parse(url));
request.allowScanningByMediaScanner();
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "download");
DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
dm.enqueue(request);
Snackbar snackbar = Snackbar.make(findViewById(android.R.id.content),"Downloading...",Snackbar.LENGTH_SHORT);
snackbar.show();
// Changing message text color
snackbar.setActionTextColor(Color.YELLOW);
}
});
/*
* Sets up a SwipeRefreshLayout.OnRefreshListener that is invoked when the user
* performs a swipe-to-refresh gesture.
*/
final SwipeRefreshLayout finalMySwipeRefreshLayout = mySwipeRefreshLayout;
mySwipeRefreshLayout.setOnRefreshListener(
new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
//Log.i(TAG, "onRefresh called from SwipeRefreshLayout");
// This method performs the actual data-refresh operation.
// The method calls setRefreshing(false) when it's finished.
myWebView.loadUrl(String.valueOf(url));
}
}
);
myWebView.setWebChromeClient(new WebChromeClient(){
public void onProgressChanged(WebView view, int newProgress){
// Update the progress bar with page loading progress
mProgressBar.setProgress(newProgress);
if(newProgress == 100){
// Hide the progressbar
mProgressBar.setVisibility(View.GONE);
}
}
});
/*btnback.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (myWebView.canGoBack()) {
myWebView.goBack();
}
}
});*/
}
private boolean isNetworkAvailable(){
ConnectivityManager connectivityManager=(ConnectivityManager)this.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo=connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo !=null;
}
public class WebViewClient extends android.webkit.WebViewClient
{
@Override
public void onPageStarted(WebView view, String url, Bitmap favicon) {
// TODO Auto-generated method stub
super.onPageStarted(view, url, favicon);
// Visible the progressbar
mProgressBar.setVisibility(View.VISIBLE);
}
public void onProgressChanged(WebView view, int newProgress){
// Update the progress bar with page loading progress
mProgressBar.setProgress(newProgress);
if(newProgress == 100){
// Hide the progressbar
mProgressBar.setVisibility(View.GONE);
}
}
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.items, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.stop) {
//myWebView.stopLoading();
} else if(id == R.id.home){
finish();
}
return true;
}
@Override
public void onBackPressed() {
if (myWebView.canGoBack()) {
myWebView.goBack();
return;
}
// Otherwise defer to system default behavior.
super.onBackPressed();
}
}
答案 0 :(得分：0)
您遇到范围问题。您的活动“ Webview”（类名错误）具有一个Webview类型的myWebView对象，该对象从未分配。将其更改为Web V iew（大写W）
然后替换
final WebView myWebView = findViewById(R.id.webview);
使用
myWebView = findViewById(R.id.webview);
答案 1 :(得分：0)
您在这里使用Webview，但实际上是WebView。
答案 2 :(得分：0)
问题编号1.使用
WebView myWebView;代替Webview myWebView;，请参见TYPO第2个问题。
final WebView myWebView = findViewById(R.id.webview);
使用
myWebView = findViewById(R.id.webview);
代替
final WebView myWebView = findViewById(R.id.webview);
问题编号3.更改活动名称
尝试一下
package com.example.nilesh.testapp;
import android.os.Bundle;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.Window;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.widget.ProgressBar;
public class WebViewActivity extends AppCompatActivity {
public String url;
private ProgressBar mProgressBar;
WebView myWebView;
@Override
protected void onCreate(Bundle savedInstanceState) {
final String url = getIntent().getStringExtra("URL");
// Request window feature action bar
requestWindowFeature(Window.FEATURE_ACTION_BAR);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_web_view);
myWebView = findViewById(R.id.webview);
myWebView.loadUrl(url);
WebSettings webSettings = myWebView.getSettings();
webSettings.setJavaScriptEnabled(true);
myWebView.getSettings().setBuiltInZoomControls(true);
myWebView.getSettings().setDefaultZoom(WebSettings.ZoomDensity.FAR);
myWebView.getSettings().setPluginState(WebSettings.PluginState.ON);
myWebView.getSettings().setAllowFileAccess(true);
// Get the widgets reference from XML layout
mProgressBar = findViewById(R.id.pb);
SwipeRefreshLayout mySwipeRefreshLayout=new SwipeRefreshLayout(this);
mySwipeRefreshLayout = (SwipeRefreshLayout) findViewById(R.id.swiperefresh);
//code to check network availability
if(!isNetworkAvailable()){
//Create an alertdialog
AlertDialog.Builder Checkbuilder=new AlertDialog.Builder(Webview.this);
Checkbuilder.setIcon(R.drawable.error);
Checkbuilder.setTitle("Error!");
Checkbuilder.setMessage("Check Your Internet Connection.");
//Builder Retry Button
Checkbuilder.setPositiveButton("Retry", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int id) {
//Restart The Activity
Intent intent = getIntent();
finish();
startActivity(intent);
}
});
Checkbuilder.setNegativeButton("Exit", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
finish();
}
}) ;
AlertDialog alert=Checkbuilder.create();
alert.show();
}
//If internet is available load the url
else {
// Request to render the web page
if (savedInstanceState == null) {
myWebView.loadUrl(url);
}
}
Configuration config = getResources().getConfiguration();
final SwipeRefreshLayout finalMySwipeRefreshLayout1 = mySwipeRefreshLayout;
myWebView.setWebViewClient(new WebViewClient() {
@Override
public void onPageStarted(WebView view, String url, Bitmap favicon) {
// TODO Auto-generated method stub
super.onPageStarted(view, url, favicon);
// Visible the progressbar
mProgressBar.setVisibility(View.VISIBLE);
}
@Override
public void onPageFinished(WebView view, String url) {
finalMySwipeRefreshLayout1.setRefreshing(false);
}
});
//Code for handling download
myWebView.setDownloadListener(new DownloadListener() {
public void onDownloadStart(String url, String userAgent,
String contentDisposition, String mimetype,
long contentLength) {
DownloadManager.Request request = new DownloadManager.Request( Uri.parse(url));
request.allowScanningByMediaScanner();
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, "download");
DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
dm.enqueue(request);
Snackbar snackbar = Snackbar.make(findViewById(android.R.id.content),"Downloading...",Snackbar.LENGTH_SHORT);
snackbar.show();
// Changing message text color
snackbar.setActionTextColor(Color.YELLOW);
}
});
/*
* Sets up a SwipeRefreshLayout.OnRefreshListener that is invoked when the user
* performs a swipe-to-refresh gesture.
*/
final SwipeRefreshLayout finalMySwipeRefreshLayout = mySwipeRefreshLayout;
mySwipeRefreshLayout.setOnRefreshListener(
new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
//Log.i(TAG, "onRefresh called from SwipeRefreshLayout");
// This method performs the actual data-refresh operation.
// The method calls setRefreshing(false) when it's finished.
myWebView.loadUrl(String.valueOf(url));
}
}
);
myWebView.setWebChromeClient(new WebChromeClient(){
public void onProgressChanged(WebView view, int newProgress){
// Update the progress bar with page loading progress
mProgressBar.setProgress(newProgress);
if(newProgress == 100){
// Hide the progressbar
mProgressBar.setVisibility(View.GONE);
}
}
});
/*btnback.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if (myWebView.canGoBack()) {
myWebView.goBack();
}
}
});*/
}
private boolean isNetworkAvailable(){
ConnectivityManager connectivityManager=(ConnectivityManager)this.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo=connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo !=null;
}
public class WebViewClient extends android.webkit.WebViewClient
{
@Override
public void onPageStarted(WebView view, String url, Bitmap favicon) {
// TODO Auto-generated method stub
super.onPageStarted(view, url, favicon);
// Visible the progressbar
mProgressBar.setVisibility(View.VISIBLE);
}
public void onProgressChanged(WebView view, int newProgress){
// Update the progress bar with page loading progress
mProgressBar.setProgress(newProgress);
if(newProgress == 100){
// Hide the progressbar
mProgressBar.setVisibility(View.GONE);
}
}
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.items, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.stop) {
//myWebView.stopLoading();
} else if(id == R.id.home){
finish();
}
return true;
}
@Override
public void onBackPressed() {
if (myWebView.canGoBack()) {
myWebView.goBack();
return;
}
// Otherwise defer to system default behavior.
super.onBackPressed();
}
}