Java 获取服务对象上的空指针异常
我正在尝试将google任务与我的应用程序同步。为此，我创建了一个名为Java 获取服务对象上的空指针异常,java,android,nullpointerexception,Java,Android,Nullpointerexception,我正在尝试将google任务与我的应用程序同步。为此，我创建了一个名为GTaskSyncer的类，其中我创建了获取任务详细信息的方法 我想从UI调用这些方法。现在，为了测试，我创建了一个类，它扩展了AsyncTask，在doInbackground中调用了这个方法 这是我在主要活动中提到的 现在我在GTaskSyncer中的服务对象上得到一个空指针异常 主要活动 public class MainActivity extends AppCompatActivity { GoogleAcc
GTaskSyncerAsyncTaskdoInbackgroundGTaskSyncerpublic class MainActivity extends AppCompatActivity {
GoogleAccountCredential mCredential;
private TextView mOutputText;
ProgressDialog mProgress;
static final int REQUEST_ACCOUNT_PICKER = 1000;
static final int REQUEST_AUTHORIZATION = 1001;
static final int REQUEST_GOOGLE_PLAY_SERVICES = 1002;
private static final String PREF_ACCOUNT_NAME = "accountName";
private static final String[] SCOPES = { TasksScopes.TASKS };
public com.google.api.services.tasks.Tasks mService = null;
/**
* Create the main activity.
* @param savedInstanceState previously saved instance data.
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LinearLayout activityLayout = new LinearLayout(this);
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.MATCH_PARENT);
activityLayout.setLayoutParams(lp);
activityLayout.setOrientation(LinearLayout.VERTICAL);
activityLayout.setPadding(16, 16, 16, 16);
ViewGroup.LayoutParams tlp = new ViewGroup.LayoutParams(
ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
mOutputText = new TextView(this);
mOutputText.setLayoutParams(tlp);
mOutputText.setPadding(16, 16, 16, 16);
mOutputText.setVerticalScrollBarEnabled(true);
mOutputText.setMovementMethod(new ScrollingMovementMethod());
activityLayout.addView(mOutputText);
mProgress = new ProgressDialog(this);
mProgress.setMessage("Calling Google Tasks API ...");
Button sync = new Button(this);
sync.setText("Sync");
setContentView(activityLayout);
// Initialize credentials and service object.
SharedPreferences settings = getPreferences(Context.MODE_PRIVATE);
mCredential = GoogleAccountCredential.usingOAuth2(
getApplicationContext(), Arrays.asList(SCOPES))
.setBackOff(new ExponentialBackOff())
.setSelectedAccountName(settings.getString(PREF_ACCOUNT_NAME, null));
HttpTransport transport = AndroidHttp.newCompatibleTransport();
JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
mService = new com.google.api.services.tasks.Tasks.Builder(
transport, jsonFactory, mCredential)
.setApplicationName("Google Tasks API Android Quickstart")
.build();
}
/**
* Called whenever this activity is pushed to the foreground, such as after
* a call to onCreate().
*/
@Override
protected void onResume() {
super.onResume();
if (isGooglePlayServicesAvailable()) {
refreshResults();
} else {
mOutputText.setText("Google Play Services required: " +
"after installing, close and relaunch this app.");
}
}
/**
* Called when an activity launched here (specifically, AccountPicker
* and authorization) exits, giving you the requestCode you started it with,
* the resultCode it returned, and any additional data from it.
* @param requestCode code indicating which activity result is incoming.
* @param resultCode code indicating the result of the incoming
* activity result.
* @param data Intent (containing result data) returned by incoming
* activity result.
*/
@Override
protected void onActivityResult(
int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
switch(requestCode) {
case REQUEST_GOOGLE_PLAY_SERVICES:
if (resultCode != RESULT_OK) {
isGooglePlayServicesAvailable();
}
break;
case REQUEST_ACCOUNT_PICKER:
if (resultCode == RESULT_OK && data != null &&
data.getExtras() != null) {
String accountName =
data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME);
if (accountName != null) {
mCredential.setSelectedAccountName(accountName);
SharedPreferences settings =
getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = settings.edit();
editor.putString(PREF_ACCOUNT_NAME, accountName);
editor.apply();
}
} else if (resultCode == RESULT_CANCELED) {
mOutputText.setText("Account unspecified.");
}
break;
case REQUEST_AUTHORIZATION:
if (resultCode != RESULT_OK) {
chooseAccount();
}
break;
}
super.onActivityResult(requestCode, resultCode, data);
}
/**
* Attempt to get a set of data from the Google Tasks API to display. If the
* email address isn't known yet, then call chooseAccount() method so the
* user can pick an account.
*/
private void refreshResults() {
if (mCredential.getSelectedAccountName() == null) {
chooseAccount();
} else {
if (isDeviceOnline()) {
new TestAsyncTask(mCredential).execute();
} else {
mOutputText.setText("No network connection available.");
}
}
}
/**
* Starts an activity in Google Play Services so the user can pick an
* account.
*/
private void chooseAccount() {
startActivityForResult(
mCredential.newChooseAccountIntent(), REQUEST_ACCOUNT_PICKER);
}
/**
* Checks whether the device currently has a network connection.
* @return true if the device has a network connection, false otherwise.
*/
private boolean isDeviceOnline() {
ConnectivityManager connMgr =
(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
return (networkInfo != null && networkInfo.isConnected());
}
/**
* Check that Google Play services APK is installed and up to date. Will
* launch an error dialog for the user to update Google Play Services if
* possible.
* @return true if Google Play Services is available and up to
* date on this device; false otherwise.
*/
private boolean isGooglePlayServicesAvailable() {
final int connectionStatusCode =
GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
if (GooglePlayServicesUtil.isUserRecoverableError(connectionStatusCode)) {
showGooglePlayServicesAvailabilityErrorDialog(connectionStatusCode);
return false;
} else if (connectionStatusCode != ConnectionResult.SUCCESS ) {
return false;
}
return true;
}
/**
* Display an error dialog showing that Google Play Services is missing
* or out of date.
* @param connectionStatusCode code describing the presence (or lack of)
* Google Play Services on this device.
*/
void showGooglePlayServicesAvailabilityErrorDialog(
final int connectionStatusCode) {
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(
connectionStatusCode,
MainActivity.this,
REQUEST_GOOGLE_PLAY_SERVICES);
dialog.show();
}
}
public class TestAsyncTask extends AsyncTask<Void, Void, List<TaskList>>{
private com.google.api.services.tasks.Tasks mService = null;
private Exception mLastError = null;
private MainActivity activity;
private com.google.api.services.tasks.Tasks client = null;
public TestAsyncTask(GoogleAccountCredential credential) {
HttpTransport transport = AndroidHttp.newCompatibleTransport();
JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
mService = new com.google.api.services.tasks.Tasks.Builder(
transport, jsonFactory, credential)
.setApplicationName("Google Tasks API Android Quickstart")
.build();
}
protected List<TaskList> doInBackground(Void... params) {
GTaskSyncer gTaskSyncer = new GTaskSyncer(activity);
List<TaskList> result = new ArrayList<>();
try {
result = gTaskSyncer.getAllTaskList();
} catch (IOException e) {
Toast.makeText(activity,"IO Exception",Toast.LENGTH_SHORT).show();
}
return result;
}
}
公共类TestAsyncTask扩展了AsyncTask{
private com.google.api.services.tasks.tasks mService=null；
私有异常mLastError=null；
私人活动；
private com.google.api.services.tasks.tasks客户端=null；
公共TestAsyncTask（GoogleAccountCredential凭证）{
HttpTransport-transport=AndroidHttp.newCompatibleTransport（）；
JsonFactory JsonFactory=JacksonFactory.getDefaultInstance（）；
mService=new com.google.api.services.tasks.tasks.Builder(
运输、jsonFactory、凭证）
.setApplicationName（“谷歌任务API Android快速启动”）
.build（）；
}
受保护列表doInBackground（无效…参数）{
GTaskSyncer GTaskSyncer=新的GTaskSyncer（活动）；
列表结果=新建ArrayList（）；
试一试{
结果=gTaskSyncer.getAllTaskList（）；
}捕获（IOE异常）{
Toast.makeText（活动，“IO异常”，Toast.LENGTH_SHORT）.show（）；
}
返回结果；
}
}
public class GTaskSyncer
{
final MainActivity activity;
final com.google.api.services.tasks.Tasks mService;
GTaskSyncer(MainActivity activity) {
this.activity = activity;
mService = activity.mService;
}
public List<TaskList> getAllTaskList() throws IOException
{
List<TaskList> result = new ArrayList<TaskList>();
TaskLists taskLists = mService.tasklists().list().execute();
for (TaskList taskList : taskLists.getItems()) {
result.add(taskList);
}
return result;
}
public TaskList createList() throws IOException
{
TaskList taskList = new TaskList();
taskList = activity.mService.tasklists().insert(taskList).execute();
return taskList;
}
public Task createTask(String listId) throws IOException
{
Task task = new Task();
task = activity.mService.tasks().insert(listId, task).execute();
return task;
}
public Task getTask(String listId,String taskId) throws IOException
{
Task task = activity.mService.tasks().get(listId, taskId).execute();
return task;
}
public List<Task> getTaskList(String listId) throws IOException
{
List<Task> result = new ArrayList<Task>();
List<Task> tasks = mService.tasks().list(listId).execute().getItems();
if (tasks != null) {
for (Task task : tasks) {
result.add(task);
}
} else {
Toast.makeText(activity,"No tasks.",Toast.LENGTH_SHORT).show();
}
return result;
}
}
公共类GTaskSyncer
{
最后的主要活动；
最终com.google.api.services.tasks.tasks mService；
GTaskSyncer（主要活动）{
这个。活动=活动；
mService=activity.mService；
}
public List getAllTaskList（）引发IOException
{
列表结果=新建ArrayList（）；
TaskLists TaskLists=mService.TaskLists（）.list（）.execute（）；
对于（任务列表任务列表：taskLists.getItems（））{
结果.添加（任务列表）；
}
返回结果；
}
public TaskList createList（）引发IOException
{
TaskList TaskList=新任务列表（）；
taskList=activity.mService.tasklists（）.insert（taskList.execute（）；
返回任务列表；
}
公共任务createTask（字符串listId）引发IOException
{
任务=新任务（）；
task=activity.mService.tasks（）.insert（listId，task.execute（）；
返回任务；
}
公共任务getTask（String listId，String taskId）引发IOException
{
Task Task=activity.mService.tasks（）.get（listId，taskId.execute（）；
返回任务；
}
公共列表getTaskList（字符串listId）引发IOException
{
列表结果=新建ArrayList（）；
List tasks=mService.tasks（）.List（listId.execute（）.getItems（）；
如果（任务！=null）{
for（任务：任务）{
结果。添加（任务）；
}
}否则{
Toast.makeText（活动，“无任务”，Toast.LENGTH_SHORT）.show（）；
}
返回结果；
}
}
请帮助..您尚未初始化此
私人MainActivity活动GTaskSyncerGTaskSyncer gTaskSyncer = new GTaskSyncer(activity);
GTaskSyncer(MainActivity activity) {
this.activity = activity; // null
mService = activity.mService; // exception
}
taskList = activity.mService.tasklists().insert(taskList).execute();
public TestAsyncTask(GoogleAccountCredential credential, MainActivity activity) {
HttpTransport transport = AndroidHttp.newCompatibleTransport();
JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();
mService = new com.google.api.services.tasks.Tasks.Builder(
transport, jsonFactory, credential)
.setApplicationName("Google Tasks API Android Quickstart")
.build();
this.activity = activity;
}
new TestAsyncTask(mCredential, MainActivity.this).execute();
最好更改构造函数
GTaskSyncer(MainActivity activity,com.google.api.services.tasks.Tasks mService) {
this.activity = activity;
this.mService = mService;
}
请显示您的日志输出。跟踪此问题可能会很有用。可能是重复的谢谢。。它解决了空异常。但我无法得到任何任务列表。你能帮忙吗？@user5881997，如果它解决了空指针异常，你能告诉我答案吗。你能更新获取任务列表的代码吗？它是相同的。在getAllTaskList（）的GTaskSyncer方法中，我在TestAsyncTask中调用此函数。我在主要活动中调用的TestAsyncTask。但活动是空白的。我看不到名单。我做了调试以检查列表是否为空。但这个列表有其价值@罗希塔里亚