我的应用程序在启动时成功运行，并且第一次允许访问外部存储运行时权限，但是当我第二次启动它时，它不响应任何事情并崩溃。无法理解.. 我正在开发一个简单的导航抽屉网页视图应用程序。
这是我的主要活动
import static com.izhandroid.izhandroidapps.R.id.webView;
private static final int PERMISSION_REQUEST_CODE = 1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toast.makeText(getApplicationContext(), "Please allow permission to download and save files", Toast.LENGTH_LONG).show();
setContentView(R.layout.activity_main);
if (Build.VERSION.SDK_INT >= 23) {
if (checkPermission()) {
} else {
requestPermission(); // Code for permission
}
} else {
}
}
private boolean checkPermission() {
int result = ContextCompat.checkSelfPermission(MainActivity.this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE);
if (result == PackageManager.PERMISSION_GRANTED) {
return true;
} else {
return false;
}
}
private void requestPermission() {
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, android.Manifest.permission.WRITE_EXTERNAL_STORAGE)) {
Toast.makeText(MainActivity.this, "Please go to app settings and allow permission to download files.", Toast.LENGTH_LONG).show();
} else {
ActivityCompat.requestPermissions(MainActivity.this, new String[]{android.Manifest.permission.WRITE_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
Toast.makeText(MainActivity.this, "Tip: Pull down to refresh",Toast.LENGTH_LONG).show();
}
}
@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
switch (requestCode) {
case PERMISSION_REQUEST_CODE:
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
Log.e("value", "Permission Granted, Now you can use local drive .");
} else {
Log.e("value", "Permission Denied, You cannot use local drive .");
}
break;
}
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.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
swipe = (SwipeRefreshLayout) findViewById(R.id.swipe) ;
swipe.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
LoadWeb();
}
});
LoadWeb();
}
public void LoadWeb(){
wv = (WebView) findViewById(webView);
final WebSettings settings = wv.getSettings();
settings.setJavaScriptEnabled(true);
wv.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);
wv.getSettings().setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);
wv.getSettings().setAppCacheEnabled(true);
wv.getSettings().getJavaScriptCanOpenWindowsAutomatically();
wv.getSettings().getDisplayZoomControls();
wv.getSettings().setSupportZoom(true);
wv.getSettings().setLoadsImagesAutomatically(true);
settings.getMediaPlaybackRequiresUserGesture();
swipe.setRefreshing(true);
settings.setAllowFileAccess(true);
settings.setAllowContentAccess(true);
settings.setDomStorageEnabled(true);
settings.setLayoutAlgorithm(WebSettings.LayoutAlgorithm.NARROW_COLUMNS);
settings.setUseWideViewPort(true);
settings.setEnableSmoothTransition(true);
wv.setWebViewClient(new MyWebViewClient());
//refreshLayout(this);
wv.loadUrl("http://izhandroidwebdemo.blogspot.com");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
wv.setWebViewClient(new MyWebViewClient(){
public void onReceivedError(WebView view, int errorCode, String description,String failingUrl){
wv.loadUrl("file:///android_asset/mypage.html");
}
//@Override
public void onPageFinished(WebView view, String url) {
swipe.setRefreshing(false);
// setTitle(view.getTitle());
}
});
wv.setDownloadListener(new DownloadListener() {
@Override
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, "file-webapp");
DownloadManager dm =(DownloadManager) getSystemService(DOWNLOAD_SERVICE);
dm.enqueue(request);
Toast.makeText(getApplicationContext(), "Downloading File..", Toast.LENGTH_LONG).show();
}
});
}
protected void initializeOptions() {
Intent intent = getIntent();
if (intent == null) {
return;
}
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_home) {
wv.loadUrl("http://izhandroidwebdemo.blogspot.com");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
} else if (id == R.id.nav_linkone) {
wv.loadUrl("http://www.facebook.com/mohdizhanali");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
} else if (id == R.id.nav_linktwo) {
wv.loadUrl("http://www.instagram.com/aninnocentguy");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
} else if (id == R.id.nav_linkthree) {
wv.loadUrl("http://www.google.co.in");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
} else if (id == R.id.nav_linkfour) {
wv.loadUrl("file:///android_asset/mypage.html");
} else if (id == R.id.mail) {
//wv.loadUrl("file:///android_asset/mypage.html");
Intent localIntent1 = new Intent("android.intent.action.SENDTO", Uri.fromParts("mailto", "idappshelp@gmail.com", null));
localIntent1.putExtra("android.intent.extra.SUBJECT", "Feedback");
localIntent1.putExtra("android.intent.extra.TEXT", "Hi Team,");
startActivity(Intent.createChooser(localIntent1, "Send email..."));
} else if (id == R.id.devsite) {
wv.loadUrl("http://www.izhandroidapps.blogspot.in");
Toast.makeText(getApplication(), "Loading, Please Wait...", Toast.LENGTH_LONG).show();
} else if (id == R.id.call) {
Intent i =new Intent(Intent.ACTION_DIAL);
i.setData(Uri.parse("tel:+919948918505"));
startActivity(i);
} else if (id == R.id.whatsapp) {
//startActivity(new Intent("android.intent.action.VIEW", //Uri.parse());
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://api.whatsapp.com/send?phone=919948918505&text=Hello"));
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setPackage("com.whatsapp");
startActivity(intent);
} else if (id == R.id.nav_share) {
Intent localIntent2 = new Intent("android.intent.action.SEND");
localIntent2.setType("text/plain");
localIntent2.putExtra("android.intent.extra.SUBJECT", "Spread word");
localIntent2.putExtra("android.intent.extra.TEXT", "null");
startActivity(Intent.createChooser(localIntent2, "Share via"));
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
private class MyWebViewClient extends WebViewClient {
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (event.getAction() == KeyEvent.ACTION_DOWN) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
if (wv.canGoBack()) {
wv.goBack();
} else {
finish();
}
return true;
}
}
return super.onKeyDown(keyCode, event);
}
}
我认为这是由于运行时权限 登录崩溃
块引用 java.lang.NullPointerException：尝试在空对象引用上调用虚方法'boolean android.webkit.WebView.canGoBack（）' 在com.izhandroid.izhandroidapps.MainActivity.onKeyDown（MainActivity.java:345） 在android.view.KeyEvent.dispatch（KeyEvent.java:2694） 在android.app.Activity.dispatchKeyEvent（Activity.java:3115） 在android.support.v7.app.AppCompatActivity.dispatchKeyEvent（AppCompatActivity.java:534） 在android.support.v7.view.WindowCallbackWrapper.dispatchKeyEvent（WindowCallbackWrapper.java:58） 在android.support.v7.app.AppCompatDelegateImplBase $ AppCompatWindowCallbackBase.dispatchKeyEvent（AppCompatDelegateImplBase.java:316） 在com.android.internal.policy.DecorView.dispatchKeyEvent（DecorView.java:323） 在android.view.ViewRootImpl $ ViewPostImeInputStage.processKeyEvent（ViewRootImpl.java:4390） 在android.view.ViewRootImpl $ ViewPostImeInputStage.onProcess（ViewRootImpl.java:4361） 在android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3905） 在android.view.ViewRootImpl $ InputStage.onDeliverToNext（ViewRootImpl.java:3958） 在android.view.ViewRootImpl $ InputStage.forward（ViewRootImpl.java:3924） 在android.view.ViewRootImpl $ AsyncInputStage.forward（ViewRootImpl.java:4051） 在android.view.ViewRootImpl $ InputStage.apply（ViewRootImpl.java:3932） 在android.view.ViewRootImpl $ AsyncInputStage.apply（ViewRootImpl.java:4108） 在android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3905） 在android.view.ViewRootImpl $ InputStage.onDeliverToNext（ViewRootImpl.java:3958） 在android.view.ViewRootImpl $ InputStage.forward（ViewRootImpl.java:3924） 在android.view.ViewRootImpl $ InputStage.apply（ViewRootImpl.java:3932） 在android.view.ViewRootImpl $ InputStage.deliver（ViewRootImpl.java:3905） 在android.view.ViewRootImpl $ InputStage.onDeliverToNext（ViewRootImpl.java:3958） 在android.view.ViewRootImpl $ InputStage.forward（ViewRootImpl.java:3924） 在android.view.ViewRootImpl $ AsyncInputStage.forward（ViewRootImpl.java:4084） 在android.view.ViewRootImpl $ ImeInputStage.onFinishedInputEvent（ViewRootImpl.java:4252） 在android.view.inputmethod.InputMethodManager $ PendingEvent.run（InputMethodManager.java:2437） 在android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback（InputMethodManager.java:2001） 在android.view.inputmethod.InputMethodManager.finishedInputEvent（InputMethodManager.java:1992） 在android.view.inputmethod.InputMethodManager $ ImeInputEventSender.onInputEventFinished（InputMethodManager.java:2414） 在android.view.InputEventSender.dispatchInputEventFinished（InputEventSender.java:141） 在android.os.MessageQueue.nativePollOnce（本机方法） 在android.os.MessageQueue.next（MessageQueue.java:323） 在android.os.Looper.loop（Looper.java:142） 在android.app.ActivityThread.main（ActivityThread.java:6221） at java.lang.reflect.Method.invoke（Native Method） 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:904） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:794）
这是屏幕截图
