我正在尝试为我的论坛创建一个应用程序，以便用户不必在其移动设备上使用浏览器或使用另一个应用程序。我正在遇到该应用程序现在崩溃的问题，但不确定为什么。我是一个新手，所以真的不知道代码错误时要寻找什么，也许我可以帮助弄清楚自己做错了什么？
我可能需要更改代码中的内容，因此请随时让我知道，但要告诉我需要更改的内容。我还需要弄清楚如何在应用程序中添加复制和糊状功能，并可以为应用程序设置cookie的"记住我"。
package com.technologx.technologx;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.DownloadManager;
import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.MediaStore;
import android.view.View;
import android.view.Window;
import android.webkit.CookieSyncManager;
import android.webkit.JsResult;
import android.webkit.ValueCallback;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebSettings.PluginState;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;
import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
public class MainActivity extends Activity {
private WebView webView;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Adds Progress Bar Support
this.getWindow().requestFeature(Window.FEATURE_PROGRESS);
// Makes Progress Bar Visible
getWindow().setFeatureInt( Window.FEATURE_PROGRESS, Window.PROGRESS_VISIBILITY_ON);
// Use forum.xml as webview layout
setContentView(R.layout.activity_main);
webView.setWebViewClient(new WebViewClient());
webView = (WebView) findViewById(R.id.activity_main_webview);
webView.getSettings().setJavaScriptEnabled(true);
// Adds Zoom Control (You may not need this)
webView.getSettings().setSupportZoom(true);
// Enables Multi-Touch. if supported by ROM
webView.getSettings().setBuiltInZoomControls(true);
initWebView(webView);
webView.loadUrl("https://technologx.com"); // TODO input your url
// This will handle downloading. It requires Gingerbread, though
final DownloadManager manager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
// This is where downloaded files will be written, using the package name isn't required
// but it's a good way to communicate who owns the directory
final File destinationDir = new File (Environment.getExternalStorageDirectory(), getPackageName());
if (!destinationDir.exists()) {
destinationDir.mkdir(); // Don't forget to make the directory if it's not there
}
webView.setWebViewClient(new WebViewClient() {
@Override
public boolean shouldOverrideUrlLoading (WebView view, String url) {
boolean shouldOverride = false;
// We only want to handle requests for mp3 files, everything else the webview
// can handle normally
if (url.endsWith(".zip")) {
shouldOverride = true;
Uri source = Uri.parse(url);
// Make a new request pointing to the mp3 url
DownloadManager.Request request = new DownloadManager.Request(source);
// Use the same file name for the destination
File destinationFile = new File (destinationDir, source.getLastPathSegment());
request.setDestinationUri(Uri.fromFile(destinationFile));
// Add it to the manager
manager.enqueue(request);
}
return shouldOverride;
}
});
}
private final static Object methodInvoke(Object obj, String method, Class<?>[] parameterTypes, Object[] args) {
try {
Method m = obj.getClass().getMethod(method, new Class[] { boolean.class });
m.invoke(obj, args);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
private void initWebView(WebView webView) {
WebSettings settings = webView.getSettings();
settings.setJavaScriptEnabled(true);
settings.setAllowFileAccess(true);
settings.setDomStorageEnabled(true);
settings.setCacheMode(WebSettings.LOAD_NO_CACHE);
settings.setLoadWithOverviewMode(true);
settings.setUseWideViewPort(true);
settings.setSupportZoom(true);
// settings.setPluginsEnabled(true);
methodInvoke(settings, "setPluginsEnabled", new Class[] { boolean.class }, new Object[] { true });
// settings.setPluginState(PluginState.ON);
methodInvoke(settings, "setPluginState", new Class[] { PluginState.class }, new Object[] { PluginState.ON });
// settings.setPluginsEnabled(true);
methodInvoke(settings, "setPluginsEnabled", new Class[] { boolean.class }, new Object[] { true });
// settings.setAllowUniversalAccessFromFileURLs(true);
methodInvoke(settings, "setAllowUniversalAccessFromFileURLs", new Class[] { boolean.class }, new Object[] { true });
// settings.setAllowFileAccessFromFileURLs(true);
methodInvoke(settings, "setAllowFileAccessFromFileURLs", new Class[] { boolean.class }, new Object[] { true });
webView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
webView.clearHistory();
webView.clearFormData();
webView.clearCache(true);
webView.setWebChromeClient(new MyWebChromeClient());
// webView.setDownloadListener(downloadListener);
}
UploadHandler mUploadHandler;
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
if (requestCode == Controller.FILE_SELECTED) {
// Chose a file from the file picker.
if (mUploadHandler != null) {
mUploadHandler.onResult(resultCode, intent);
}
}
super.onActivityResult(requestCode, resultCode, intent);
}
class MyWebChromeClient extends WebChromeClient {
public MyWebChromeClient() {
}
private String getTitleFromUrl(String url) {
String title = url;
try {
URL urlObj = new URL(url);
String host = urlObj.getHost();
if (host != null && !host.isEmpty()) {
return urlObj.getProtocol() + "://" + host;
}
if (url.startsWith("file:")) {
String fileName = urlObj.getFile();
if (fileName != null && !fileName.isEmpty()) {
return fileName;
}
}
} catch (Exception e) {
// ignore
}
return title;
}
@Override
public boolean onJsAlert(WebView view, String url, String message, final JsResult result) {
String newTitle = getTitleFromUrl(url);
new AlertDialog.Builder(MainActivity.this).setTitle(newTitle).setMessage(message).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
result.confirm();
}
}).setCancelable(false).create().show();
return true;
// return super.onJsAlert(view, url, message, result);
}
@Override
public boolean onJsConfirm(WebView view, String url, String message, final JsResult result) {
String newTitle = getTitleFromUrl(url);
new AlertDialog.Builder(MainActivity.this).setTitle(newTitle).setMessage(message).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
result.confirm();
}
}).setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
result.cancel();
}
}).setCancelable(false).create().show();
return true;
// return super.onJsConfirm(view, url, message, result);
}
// Android 2.x
public void openFileChooser(ValueCallback<Uri> uploadMsg) {
openFileChooser(uploadMsg, "");
}
// Android 3.0
public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType) {
openFileChooser(uploadMsg, "", "filesystem");
}
// Android 4.1
public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
mUploadHandler = new UploadHandler(new Controller());
mUploadHandler.openFileChooser(uploadMsg, acceptType, capture);
}
// Android 4.4, 4.4.1, 4.4.2
// openFileChooser function is not called on Android 4.4, 4.4.1, 4.4.2,
// you may use your own java script interface or other hybrid framework.
// Android 5.0.1
public boolean onShowFileChooser(
WebView webView, ValueCallback<Uri[]> filePathCallback,
FileChooserParams fileChooserParams) {
String acceptTypes[] = fileChooserParams.getAcceptTypes();
String acceptType = "";
for (int i = 0; i < acceptTypes.length; ++ i) {
if (acceptTypes[i] != null && acceptTypes[i].length() != 0)
acceptType += acceptTypes[i] + ";";
}
if (acceptType.length() == 0)
acceptType = "*/*";
final ValueCallback<Uri[]> finalFilePathCallback = filePathCallback;
ValueCallback<Uri> vc = new ValueCallback<Uri>() {
@Override
public void onReceiveValue(Uri value) {
Uri[] result;
if (value != null)
result = new Uri[]{value};
else
result = null;
finalFilePathCallback.onReceiveValue(result);
}
};
openFileChooser(vc, acceptType, "filesystem");
return true;
}
};
class Controller {
final static int FILE_SELECTED = 4;
Activity getActivity() {
return MainActivity.this;
}
}
// public class UploadHandler {
class UploadHandler {
/*
* The Object used to inform the WebView of the file to upload.
*/
private ValueCallback<Uri> mUploadMessage;
private String mCameraFilePath;
private boolean mHandled;
private boolean mCaughtActivityNotFoundException;
private Controller mController;
public UploadHandler(Controller controller) {
mController = controller;
}
String getFilePath() {
return mCameraFilePath;
}
boolean handled() {
return mHandled;
}
void onResult(int resultCode, Intent intent) {
if (resultCode == Activity.RESULT_CANCELED && mCaughtActivityNotFoundException) {
// Couldn't resolve an activity, we are going to try again so skip
// this result.
mCaughtActivityNotFoundException = false;
return;
}
Uri result = intent == null || resultCode != Activity.RESULT_OK ? null
: intent.getData();
// As we ask the camera to save the result of the user taking
// a picture, the camera application does not return anything other
// than RESULT_OK. So we need to check whether the file we expected
// was written to disk in the in the case that we
// did not get an intent returned but did get a RESULT_OK. If it was,
// we assume that this result has came back from the camera.
if (result == null && intent == null && resultCode == Activity.RESULT_OK) {
File cameraFile = new File(mCameraFilePath);
if (cameraFile.exists()) {
result = Uri.fromFile(cameraFile);
// Broadcast to the media scanner that we have a new photo
// so it will be added into the gallery for the user.
mController.getActivity().sendBroadcast(
new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, result));
}
}
mUploadMessage.onReceiveValue(result);
mHandled = true;
mCaughtActivityNotFoundException = false;
}
void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
final String imageMimeType = "image/*";
final String videoMimeType = "video/*";
final String audioMimeType = "audio/*";
final String mediaSourceKey = "capture";
final String mediaSourceValueCamera = "camera";
final String mediaSourceValueFileSystem = "filesystem";
final String mediaSourceValueCamcorder = "camcorder";
final String mediaSourceValueMicrophone = "microphone";
// According to the spec, media source can be 'filesystem' or 'camera' or 'camcorder'
// or 'microphone' and the default value should be 'filesystem'.
String mediaSource = mediaSourceValueFileSystem;
if (mUploadMessage != null) {
// Already a file picker operation in progress.
return;
}
mUploadMessage = uploadMsg;
// Parse the accept type.
String params[] = acceptType.split(";");
String mimeType = params[0];
if (capture.length() > 0) {
mediaSource = capture;
}
if (capture.equals(mediaSourceValueFileSystem)) {
// To maintain backwards compatibility with the previous implementation
// of the media capture API, if the value of the 'capture' attribute is
// "filesystem", we should examine the accept-type for a MIME type that
// may specify a different capture value.
for (String p : params) {
String[] keyValue = p.split("=");
if (keyValue.length == 2) {
// Process key=value parameters.
if (mediaSourceKey.equals(keyValue[0])) {
mediaSource = keyValue[1];
}
}
}
}
//Ensure it is not still set from a previous upload.
mCameraFilePath = null;
if (mimeType.equals(imageMimeType)) {
if (mediaSource.equals(mediaSourceValueCamera)) {
// Specified 'image/*' and requested the camera, so go ahead and launch the
// camera directly.
startActivity(createCameraIntent());
return;
} else {
// Specified just 'image/*', capture=filesystem, or an invalid capture parameter.
// In all these cases we show a traditional picker filetered on accept type
// so launch an intent for both the Camera and image/* OPENABLE.
Intent chooser = createChooserIntent(createCameraIntent());
chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(imageMimeType));
startActivity(chooser);
return;
}
} else if (mimeType.equals(videoMimeType)) {
if (mediaSource.equals(mediaSourceValueCamcorder)) {
// Specified 'video/*' and requested the camcorder, so go ahead and launch the
// camcorder directly.
startActivity(createCamcorderIntent());
return;
} else {
// Specified just 'video/*', capture=filesystem or an invalid capture parameter.
// In all these cases we show an intent for the traditional file picker, filtered
// on accept type so launch an intent for both camcorder and video/* OPENABLE.
Intent chooser = createChooserIntent(createCamcorderIntent());
chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(videoMimeType));
startActivity(chooser);
return;
}
} else if (mimeType.equals(audioMimeType)) {
if (mediaSource.equals(mediaSourceValueMicrophone)) {
// Specified 'audio/*' and requested microphone, so go ahead and launch the sound
// recorder.
startActivity(createSoundRecorderIntent());
return;
} else {
// Specified just 'audio/*', capture=filesystem of an invalid capture parameter.
// In all these cases so go ahead and launch an intent for both the sound
// recorder and audio/* OPENABLE.
Intent chooser = createChooserIntent(createSoundRecorderIntent());
chooser.putExtra(Intent.EXTRA_INTENT, createOpenableIntent(audioMimeType));
startActivity(chooser);
return;
}
}
// No special handling based on the accept type was necessary, so trigger the default
// file upload chooser.
startActivity(createDefaultOpenableIntent());
}
private void startActivity(Intent intent) {
try {
mController.getActivity().startActivityForResult(intent, Controller.FILE_SELECTED);
} catch (ActivityNotFoundException e) {
// No installed app was able to handle the intent that
// we sent, so fallback to the default file upload control.
try {
mCaughtActivityNotFoundException = true;
mController.getActivity().startActivityForResult(createDefaultOpenableIntent(),
Controller.FILE_SELECTED);
} catch (ActivityNotFoundException e2) {
// Nothing can return us a file, so file upload is effectively disabled.
Toast.makeText(mController.getActivity(), R.string.uploads_disabled,
Toast.LENGTH_LONG).show();
}
}
}
private Intent createDefaultOpenableIntent() {
// Create and return a chooser with the default OPENABLE
// actions including the camera, camcorder and sound
// recorder where available.
Intent i = new Intent(Intent.ACTION_GET_CONTENT);
i.addCategory(Intent.CATEGORY_OPENABLE);
i.setType("*/*");
Intent chooser = createChooserIntent(createCameraIntent(), createCamcorderIntent(),
createSoundRecorderIntent());
chooser.putExtra(Intent.EXTRA_INTENT, i);
return chooser;
}
private Intent createChooserIntent(Intent... intents) {
Intent chooser = new Intent(Intent.ACTION_CHOOSER);
chooser.putExtra(Intent.EXTRA_INITIAL_INTENTS, intents);
chooser.putExtra(Intent.EXTRA_TITLE,
mController.getActivity().getResources()
.getString(R.string.choose_upload));
return chooser;
}
private Intent createOpenableIntent(String type) {
Intent i = new Intent(Intent.ACTION_GET_CONTENT);
i.addCategory(Intent.CATEGORY_OPENABLE);
i.setType(type);
return i;
}
private Intent createCameraIntent() {
Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
File externalDataDir = Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_DCIM);
File cameraDataDir = new File(externalDataDir.getAbsolutePath() +
File.separator + "browser-photos");
cameraDataDir.mkdirs();
mCameraFilePath = cameraDataDir.getAbsolutePath() + File.separator +
System.currentTimeMillis() + ".jpg";
cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(new File(mCameraFilePath)));
return cameraIntent;
}
private Intent createCamcorderIntent() {
return new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
}
private Intent createSoundRecorderIntent() {
return new Intent(MediaStore.Audio.Media.RECORD_SOUND_ACTION);
}
public void onPageFinished(WebView view, String url) {
// Removes Progress Bar
findViewById(R.id.progressbar).setVisibility(View.GONE);
// Adds Cookies. Yummy!
CookieSyncManager.getInstance().sync();
}
}
@Override
public void onBackPressed() {
// Enables going back history
if (webView.copyBackForwardList().getCurrentIndex() > 0) {
webView.goBack();
}
else {
// Your exit alert code, or alternatively line below to finish
// Finishes forum activity
super.onBackPressed();
}
}
}
这是logcat数据：
12 - 18 03: 12: 53.095 28851 - 28851 / com.technologx.technologx E / AndroidRuntime: FATAL EXCEPTION:
main
Process: com.technologx.technologx, PID: 28851
java.lang.RuntimeException: Unable to start activity ComponentInfo {
com.technologx.technologx / com.technologx.technologx.MainActivity
}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)'
on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java: 2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java: 2441)
at android.app.ActivityThread.access$800(ActivityThread.java: 162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java: 1349)
at android.os.Handler.dispatchMessage(Handler.java: 102)
at android.os.Looper.loop(Looper.java: 135)
at android.app.ActivityThread.main(ActivityThread.java: 5431)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java: 372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 707)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebViewClient(android.webkit.WebViewClient)'
on a null object reference
at com.technologx.technologx.MainActivity.onCreate(MainActivity.java: 47)
at android.app.Activity.performCreate(Activity.java: 6056)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java: 1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java: 2332)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java: 2441)
at android.app.ActivityThread.access$800(ActivityThread.java: 162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java: 1349)
at android.os.Handler.dispatchMessage(Handler.java: 102)
at android.os.Looper.loop(Looper.java: 135)
at android.app.ActivityThread.main(ActivityThread.java: 5431)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java: 372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 707)
注意我不是Java程序员。但是，当您声明此信息时，它将是一个无效的对象参考：
private WebView webView;
因此，在这两行中，您正在尝试使用此（null）对象进行操作，然后将对象设置为一个实例（大概不是null）：
webView.setWebViewClient(new WebViewClient());
webView = (WebView) findViewById(R.id.activity_main_webview);
这与您的错误一致：
引起的是：java.lang.nullpointerexception：尝试调用虚拟方法'void android.webkit.webview.setwebview.setwebviewclient（android.webkit.webviewclient）'' 在null对象引用
上
null的对象根本不是一个对象，它只是空的，因此您无法在其上执行操作。为什么不尝试交换最后两行，看看是否有帮助？