The Q&A is currently a subject of meta discussion, do participate. The current plan is to split where possible into Q&As. Answers to the A&A are community wiki and the question should become one when the status is resolved.
Preface
This Q&A strives to become a collection and a reference target for common errors encountered during development in Google Apps Script language in hopes to improve long-term maintainability of google-apps-script tag.
There are several similar and successful undergoings in other languages and general-purpose tags (see c++, android, php, php again), and this one follows suit.
Why it exists?
The amount of questions from both new and experienced developers regarding the meaning and solutions to errors encountered during development and production that can be effectively reduced to a single answer is substantial. At the time of writing, even running a query only by language tag yields:
"Cannot find method" 8 pages
"Cannot read property" 9 pages
"Cannot call ... in this context" 5 pages
"You do not have permission" 11 pages
Linking to a most relevant duplicate is hard and time-consuming for volunteers due to the need to consider nuances and often poorly-worded titles.
What it consists of?
Entries in this Q&A contain are designed to provide info on how to:
parse the error message structure
understand what the error entails
consistently reproduce (where applicable)
resolve the issue
provide a link to canonical Q&A (where possible)
Table of Contents
To help you navigate the growing reference please use the TOC below:
General errors
Service-specific errors
What this is not?
The scope of the Q&A is limited to common (not trivial). This is not:
a catch-all guide or "best practices" collection
a reference for general ECMAScript errors
GAS documentation
a resources list (we have a tag wiki for that)
What to add?
When adding an entry, please, consider the following:
is the error common enough (see "why" section for examples)?
can the solution be described concisely and be applicable for most cases?
Preface
The answer provides a guide on general errors that can be encountered when working with any Google service (both built-in and advanced) or API. For errors specific to certain services, see the other answer.
Back to reference
General errors
Message
TypeError: Cannot read property 'property name here' from undefined (or null)
Description
The error message indicates that you are trying to access a property on an Object instance, but during runtime the value actually held by a variable is a special data type undefined. Typically, the error occurs when accessing nested properties of an object.
A variation of this error with a numeric value in place of property name indicates that an instance of Array was expected. As arrays in JavaScript are objects, everything mentioned here is true about them as well.
There is a special case of dynamically constructed objects such as event objects that are only available in specific contexts like making an HTTP request to the app or invoking a function via time or event-based trigger.
The error is a TypeError because an "object" is expected, but "undefined" is received
How to fix
Using default values
Logical OR || operator in JavaScript has an intersting property of evaluating the right-hand side iff the left-hand is falsy. Since objects in JS are truthy, and undefined and null are falsy, an expression like (myVar || {}).myProp [(myVar || [])[index] for arrays] will guarantee that no error is thrown and the property is at least undefined.
One can also provide default values: (myVar || { myProp : 2 }) guarantees accessing myProp to return 2 by default. Same goes for arrays: (myVar || [1,2,3]).
Checking for type
Especially true for the special case, typeof operator combined with an if statement and a comparison operator will either allow a function to run outside of its designated context (i.e. for debugging purposes) or introduce branching logic depending on whether the object is present or not.
One can control how strict the check should be:
lax ("not undefined"): if(typeof myVar !== "undefined") { //do something; }
strict ("proper objects only"): if(typeof myVar === "object" && myVar) { //do stuff }
Related Q&As
Parsing order of the GAS project as the source of the issue
Message
Cannot convert some value to data type
Description
The error is thrown due to passing an argument of different type than a method expects. A common mistake that causes the error is accidental coercion of a number to string.
How to reproduce
function testConversionError() {
const ss = SpreadsheetApp.getActiveSheet();
ss.getRange("42.0",1);
}
How to fix
Make sure that the value referenced in the error message is of data type required by documentation and convert as needed.
Message
Cannot call Service and method name from this context
Description
This error happens on a context mismatch and is specific to container-bound scripts.
The primary use case that results in the error is trying to call a method only available in one document type (usually, getUi() as it is shared by several services) from another (i.e. DocumentApp.getUi() from a spreadsheet).
A secondary, but also prominent case is a result of calling a service not explicitly allowed to be called from a custom function (usually a function marked by special JSDoc-style comment #customfunction and used as a formula).
How to reproduce
For bound script context mismatch, declare and run this function in a script project tied to Google Sheets (or anything other than Google Docs):
function testContextMismatch() {
const doc = DocumentApp.getUi();
}
Note that calling a DocumentApp.getActiveDocument() will simply result in null on mismatch, and the execution will succeed.
For custom functions, use the function declared below in any cell as a formula:
/**
* #customfunction
*/
function testConversionError() {
const ui = SpreadsheetApp.getUi();
ui.alert(`UI is out of scope of custom function`);
}
How to fix
Context mismatch is easily fixed by changing the service on which the method is called.
Custom functions cannot be made to call these services, use custom menus or dialogs.
Message
Cannot find method Method name here
The parameters param names do not match the method signature for method name
Description
This error has a notoriously confusing message for newcomers. What it says is that a type mismatch occurred in one or more of the arguments passed when the method in question was called.
There is no method with the signature that corresponds to how you called it, hence "not found"
How to fix
The only fix here is to read the documentation carefully and check if order and inferred type of parameters are correct (using a good IDE with autocomplete will help). Sometimes, though, the issue happens because one expects the value to be of a certain type while at runtime it is of another. There are several tips for preventing such issues:
Setting up type guards (typeof myVar === "string" and similar).
Adding a validator to fix the type dynamically thanks to JavaScript being dynamically typed.
Sample
/**
* #summary pure arg validator boilerplate
* #param {function (any) : any}
* #param {...any} args
* #returns {any[]}
*/
const validate = (guard, ...args) => args.map(guard);
const functionWithValidator = (...args) => {
const guard = (arg) => typeof arg !== "number" ? parseInt(arg) : arg;
const [a,b,c] = validate(guard, ...args);
const asObject = { a, b, c };
console.log(asObject);
return asObject;
};
//driver IIFE
(() => {
functionWithValidator("1 apple",2,"0x5");
})()
Messages
You do not have permission to perform that action
The script does not have permission to perform that action
Description
The error indicates that one of the APIs or services accessed lacks sufficient permissions from the user. Every service method that has an authorization section in its documentation requires at least one of the scopes to be authorized.
As GAS essentially wraps around Google APIs for development convenience, most of the scopes listed in OAuth 2.0 scopes for APIs reference can be used, although if one is listed in the corresponding docs it may be better to use it as there are some inconsistencies.
Note that custom functions run without authorization. Calling a function from a Google sheet cell is the most common cause of this error.
How to fix
If a function calling the service is ran from the script editor, you are automatically prompted to authorize it with relevant scopes. Albeit useful for quick manual tests, it is best practice to set scopes explicitly in application manifest (appscript.json). Besides, automatic scopes are usually too broad to pass the review if one intends to publish the app.
The field oauthScopes in manifest file (View -> Show manifest file if in code editor) should look something like this:
"oauthScopes": [
"https://www.googleapis.com/auth/script.container.ui",
"https://www.googleapis.com/auth/userinfo.email",
//etc
]
For custom functions, you can fix it by switching to calling the function from a menu or a button as custom functions cannot be authorized.
For those developing editor Add-ons, this error means an unhandled authorization lifecycle mode: one has to abort before calls to services that require authorization in case auth mode is AuthMode.NONE.
Related causes and solutions
#OnlyCurrentDoc limiting script access scope
Scopes autodetection
Message
ReferenceError: service name is not defined
Description
The most common cause is using an advanced service without enabling it. When such a service is enabled, a variable under the specified identifier is attached to global scope that the developer can reference directly. Thus, when a disabled service is referenced, a ReferenceError is thrown.
How to fix
Go to "Resources -> Advanced Google Services" menu and enable the service referenced. Note that the identifier should equal the global variable referenced.
For a more detailed explanation, read the official guide.
If one hasn't referenced any advanced services then the error points to an undeclared variable being referenced.
Message
The script completed but did not return anything.
Script function not found: doGet or doPost
Description
This is not an error per se (as the HTTP response code returned is 200 and the execution is marked as successful, but is commonly regarded as one. The message appears when trying to make a request/access from browser a script deployed as a Web App.
There are two primary reasons why this would happen:
There is no doGet or doPost trigger function
Triggers above do not return an HtmlOutput or TextOutput instance
How to fix
For the first reason, simply provide a doGet or doPost trigger (or both) function. For the second, make sure that all routes of your app end with creation of TextOutput or HtmlOutput:
//doGet returning HTML
function doGet(e) {
return HtmlService.createHtmlOutput("<p>Some text</p>");
}
//doPost returning text
function doPost(e) {
const { parameters } = e;
const echoed = JSON.stringify(parameters);
return ContentService.createTextOutput(echoed);
}
Note that there should be only one trigger function declared - treat them as entry points to your application.
If the trigger relies on parameter / parameters to route responses, make sure that the request URL is structured as "baseURL/exec?query" or "baseURL/dev?query" where query contains parameters to pass.
Related Q&As
Redeploying after declaring triggers
Message
We're sorry, a server error occurred. Please wait a bit and try again.
Description
This one is the most cryptic error and can occur at any point with nearly any service (although DriveApp usage is particularly susceptible to it). The error usually indicates a problem on Google's side that either goes away in a couple of hours/days or gets fixed in the process.
How to fix
There is no silver bullet for that one and usually, there is nothing you can do apart from filing an issue on the issue tracker or contacting support if you have a GSuite account. Before doing that one can try the following common remedies:
For bound scripts - creating a new document and copying over the existing project and data.
Switch to using an advanced Drive service (always remember to enable it first).
There might be a problem with a regular expression if the error points to a line with one.
Don't bash your head against this error - try locating affected code, file or star an issue and move on
Syntax error without apparent issues
This error is likely to be caused by using an ES6 syntax (for example, arrow functions) while using the deprecated Rhino runtime (at the time of writing the GAS platform uses V8).
How to fix
Open "appscript.json" manifest file and check if runtimeVersion is set to "V8", change it if not, or remove any ES6 features otherwise.
Quota-related errors
There are several errors related to quotas imposed on service usage. Google has a comprehensive list of those, but as a general rule of thumb, if a message matches "too many" pattern, you are likely to have exceeded the respective quota.
Most likely errors encountered:
Service invoked too many times: service name
There are too many scripts running
Service using too much computer time for one day
This script has too many triggers
How to fix
In most cases, the only fix is to wait until the quota is refreshed or switch to another account (unless the script is deployed as a Web App with permission to "run as me", in which case owner's quotas will be shared across all users).
To quote documentation at the time:
Daily quotas are refreshed at the end of a 24-hour window; the exact time of this refresh, however, varies between users.
Note that some services such as MailApp have methods like getRemainingDailyQuota that can check the remaining quota.
In the case of exceeding the maximum number of triggers one can check how many are installed via getProjectTriggers() (or check "My triggers" tab) and act accordingly to reduce the number (for example, by using deleteTrigger(trigger) to get rid of some).
Related canonical Q&As
How are daily limitations being applied and refreshed?
"Maximum execution time exceeded" problem
Optimizing service calls to reduce execution time
References
How to make error messages more meaningful
Debugging custom functions
Service-specific errors
The answer concerns built-in service-related errors. For general reference see the other answer. Entries addressing issues with services listed in official reference are welcome.
Back to reference
SpreadsheetApp
The number of rows in the range must be at least 1
This error is usually caused by calling the getRange method where the parameter that sets the number of rows happens to equal to 0. Be careful if you depend on getLastRow() call return value - only use it on non-empty sheets (getDataRange will be safer).
How to reproduce
sh.getRange(1, 1, 0, sh.getLastColumn()); //third param is the number of rows
How to fix
Adding a guard that prevents the value from ever becoming 0 should suffice. The pattern below defaults to the last row with data (optional if you only need a certain number of rows) and to 1 if that also fails:
//willFail is defined elsewhere
sh.getRange(1, 1, willFail || sh.getLastRow() || 1, sh.getLastColumn());
Error: “Reference does not exist”
The error happens when calling a custom function in a spreadsheet cell that does not return a value. The docs do mention only that one "must return a value to display", but the catch here is that an empty array is also not a valid return value (no elements to display).
How to reproduce
Call the custom function below in any Google Sheets spreadsheet cell:
/**
* #customfunction
*/
const testReferenceError = () => [];
How to fix
No specific handling is required, just make sure that length > 0.
The number of rows or cells in the data does not match the number of rows or cells in the range. The data has N but the range has M.
Description
The error points to a mismatch in dimensions of range in relation to values. Usually, the issue arises when using setValues() method when the matrix of values is smaller or bigger than the range.
How to reproduce
function testOutOfRange() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sh = ss.getActiveSheet();
const rng = sh.getActiveRange();
const vals = rng.getValues();
try {
vals.push([]);
rng.setValues(vals);
} catch (error) {
const ui = SpreadsheetApp.getUi();
ui.alert(error.message);
}
}
How to fix
If it is routinely expected for values to get out of bounds, implement a guard that catches such states, for example:
const checkBounds = (rng, values) => {
const targetRows = rng.getHeight();
const targetCols = rng.getWidth();
const { length } = values;
const [firstRow] = values;
return length === targetRows &&
firstRow.length === targetCols;
};
The coordinates of the range are outside the dimensions of the sheet.
Description
The error is a result of a collision between two issues:
The Range is out of bounds (getRange() does not throw on requesting a non-existent range)
Trying to call a method on a Range instance referring to a non-existent dimension of the sheet.
How to reproduce
function testOB() {
const ss = SpreadsheetApp.getActiveSpreadsheet();
const sh = ss.getActiveSheet();
const rng = sh.getRange(sh.getMaxRows() + 1, 1);
rng.insertCheckboxes();
}
How to fix
Check that number of rows (getMaxRow()) and columns (getMaxColumns()) are both greater or equal to the parameters passed to getRange() method call and change them accordingly.
Exception: You can't create a filter in a sheet that already has a filter.
Description
The message means that you are trying to call a createFilter method on a Range in a Sheet that already has a filter set (either via UI or script), thus violating the restriction on 1 filter per Sheet, to quote the documentation:
There can be at most one filter in a sheet.
How to reproduce
const testFilterExistsError = () => {
const sh = SpreadsheetApp.getActiveSheet();
const rng = sh.getDataRange();
const filter1 = rng.createFilter();
const filter2 = rng.createFilter();
};
How to fix
Add a guard that checks for the existence of the filter first. getFilter returns either a filter or null if called on a Range instance and is perfect for the job:
const testFilterGuard = () => {
const sh = SpreadsheetApp.getActiveSheet();
const rng = sh.getDataRange();
const filter = rng.getFilter() || rng.createFilter();
//do something useful;
};
UrlFetchApp
Attribute provided with no value: url
Description
The error is specific to UrlFetchApp service and happens when fetch or fetchAll method gets called with an empty string or non-string value.
How to reproduce
const response = UrlFetchApp.fetch("", {});
How to fix
Make sure that a string containing a URI (not necessarily valid) is passed to the method as its first argument. As its common root cause is accessing a non-existent property on an object or array, check whether your accessors return an actual value.
I've read the greendao documentation and didn't find any clue about a way to be warned if, for some reason, an update fails for an entity...
the update(T entity) neither returns anything nor throws any error...
so is there any way to know if the update process has failed?
thank you.
If the update doesn't work you are getting a SQLException. Since SQLException extends [RuntimeException][2] it doesn't have to be handled and thus doesn't have to be declared withthrows`.
The only reasons for updatefailure I can think of at the moment:
The primary key in your update-object is empty.
The primary key of your update-object isn't found in your db.
The update violates some constraints (i.e. unique).
The database or filesystem is corrupted.
So normally, if you are sure you won't violate constraints and if you are careful with primary key your updates won't fail.
If you are not sure you can surround your update with try-catch-block.
try {
myEntityDao.update(myObj);
} catch (SQLException ex) {
// handle the failure here
}
I'm targeting Android 2.2 and newer. This error was generated on a device running 4.x. I am using ORMLite 4.38 libraries.
I need to guarantee every record instance is unique for any number of devices. I was happy to see that ORMLite supports UUIDs as IDs. I've created a UUID - id abstract base class for my database record definitions. allowGeneratedIdInsert is the perfect solution. But this feature seems to cause an 'IllegalStateException: could not create data element in dao'. I tested by removing this annotation, and no issue. Put it back in...same issue. Put the base class stuff in one record definition...same issue.
LogCat also reports:
Caused by: java.sql.SQLException: Unable to run insert stmt on object - objectid: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx
public abstract class UUIDDaoEnabled<T> extends BaseDaoEnabled<T, UUID> {
//allowGeneratedIdInsert allows us to set UUID when this device db didn't create it
#DatabaseField(generatedId = true, allowGeneratedIdInsert=true)
private UUID id;
...
public void setUUIDFromSerializedSource(SerializedModelBinaryInputStream stream, Dao<T, UUID> dao) throws SQLException { //only place we can set UUIDs
if(id == null)
dao.refresh((T)this);
if(id != null)
throw new SQLException("Trying to set UUID on existing object");
id = stream.getCurrentUUID();
}
}
I'll specialize like so:
#DatabaseTable()
public class Type extends UUIDDaoEnabled<Type> { ... }
I can't explain this from the documentation for allowGeneratedIdInsert and generatedId. In fact the documentation for alloeGeneratedIdInsert says it overrides the default behavior of generatedId. It also says
This only works if the database supports this behavior
Yet, I have read in other posts that ORMLite 4.25 (?) and newer supports this behavior on Android devices. So, either that's not entirely true. Or I'm doing something stupid...anyone???
UPDATE: after thinking about it for a minute, I realized that neither allowGeneratedIdInsert support, nor inheritance can be the root cause, because I instantiate other objects based on the same abstract class. What I can't figure out is why one particular class is causing the issue. The only unique thing about the offending record type (compared to other types that create) is it is a many in a one to many, and it contains several to manies. Could these properties, combined with allowGenereatedIdInsert, be the root issue? Rather, I should ask, has anyone seen this issue in this circumstance?
UPDATE: nevermind the question. I can use updateId(...) instead of allowGeneratedIdInsert.
So I'm not sure about this but it looks to me that you are trying to insert an element twice into a table with the same UUID id. The exception is saying there is a constraints failure:
IllegalStateException: Could not create data element in dao
at BaseForeignCollection.add(BaseForeignCollection.java:57)
...
Caused by: SQLiteConstraintException: error code 19: constraint failed
If you call foreignCollection.add(...); it does the same thing as dao.create(...); -- and you can't do both of these with the same object. If you have an existing object that has already been created by the DAO and you want to associate it with another object, you should do something like:
// associate this object with another
existingObject.setForeignField(...);
// now update it in the db
existingObjectDao.update(existingObject);
You can't add it to the foreignField's foreign collection.
I had a similar problem. But it was caused by using create instead createOrUpdate to save the object.
It is also important to uninstall the application before changing this to ensure that the database has been removed and will not keep the old behavior.
Edit: createOrUpdate is very time expensive. It's better use just create with great amounts of data.
Edit 2:It is also bether to use a TransactionManager.callInTransaction.
I'm getting an NullPointerException when I insert values into to my SQLite table on Android and I don't understand why. I'm testing ContentValues and the database instance for null.
This is the insertion code:
public void insertOrIgnore(ContentValues values) {
SQLiteDatabase db = this.dbHelper.getWritableDatabase();
try {
//I added these null value checks to stop NPE, but doesn't help.
if (values != null && db != null) {
db.insertWithOnConflict(TABLE, null, values, SQLiteDatabase.CONFLICT_IGNORE);
}
} catch (SQLiteException e) {
} finally {
if (db != null) {
db.close();
}
}
}
where
public static final String TABLE = "albums";
Most of the time this code works with the data added to the database as expected. However, it sometimes and rarely generates the below error. The stack trace is from ACRA and I have not been able to isolate under what conditions this error occurs. I'm looking for pointers as to why this happens and what the conditions are. My knowledge of SQLite is beginner level.
java.lang.NullPointerException
at android.database.sqlite.SQLiteStatement.releaseAndUnlock(SQLiteStatement.java:290)
at android.database.sqlite.SQLiteStatement.executeUpdateDelete(SQLiteStatement.java:96)
at android.database.sqlite.SQLiteDatabase.executeSql(SQLiteDatabase.java:2025)
at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1965)
at android.database.sqlite.SQLiteDatabase.beginTransaction(SQLiteDatabase.java:690)
at android.database.sqlite.SQLiteDatabase.beginTransactionNonExclusive(SQLiteDatabase.java:605)
at android.database.sqlite.SQLiteStatement.acquireAndLock(SQLiteStatement.java:247)
at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:112)
at android.database.sqlite.SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1844)
at com.mydomain.myapp.albums.AlbumsData.insertOrIgnore(AlbumsData.java:89)
Line 89 is the db.insertWithOnConflict(...) call shown above.
I'm not looking for an answer with complete code necessarily but rather a pointer and explanation as to what's going wrong so I can begin to fix it myself.
EDIT:
The stack trace shows the NPE originates from line 290 of SQLiteStatement (v 4.03):
setNativeHandle(mDatabase.mNativeHandle);
So it seems the database instance is null. How can it become null during a transaction when I tested for null at the beginning of the transaction?
As mentioned here SQLiteDatabase close() function causing NullPointerException when multiple threads
The reason for your bug could be that you close the database at some point. Probably concurrently while the task that fails was not finished.
I've followed the stacktrace a bit and this is what roughly happens:
AlbumsData.insertOrIgnore(AlbumsData.java:89)
You call insertWithOnConflict, which builds the resulting sql string ("INSERT OR IGNORE INTO...") then wraps that together with the values from your ContentValues into a SQLiteStatement.
SQLiteDatabase.insertWithOnConflict(SQLiteDatabase.java:1844) - The resulting statement is to be executed now
SQLiteStatement.executeInsert(SQLiteStatement.java:112) - before the actual insert can happen, the database needs to acquire a lock.
SQLiteStatement.acquireAndLock(SQLiteStatement.java:247) - some checks happen here, the database object is as far as I can see not null at that point. Code decides that it has to start a transaction. The database object itself is as far as I can see not locked at that point.
SQLiteDatabase.beginTransactionNonExclusive(SQLiteDatabase.java:605) - just forwarding
SQLiteDatabase.beginTransaction(SQLiteDatabase.java:690) - after some checks (not sure if database has to exist here) it will try to execute execSQL("BEGIN IMMEDIATE;")
SQLiteDatabase.execSQL(SQLiteDatabase.java:1965) - just forward
SQLiteDatabase.executeSql(SQLiteDatabase.java:2025) - builds another SQLiteStatement out of "BEGIN IMMEDIATE;. This one should be executed now
SQLiteStatement.executeUpdateDelete(SQLiteStatement.java:96) - starts with checking the database lock, this seems to be okay and the database should not be null here. The statement is then executed and finally the database is to be unlocked again.
SQLiteStatement.releaseAndUnlock(SQLiteStatement.java:290) - cleans up some stuff and in the end fails with NPE because the database is null.
Line numbers don't match so there are probably vendor modifications / additions in that code.
As you can see, the code crashes before actually using the data you supplied. It was about to do
BEGIN TRANSACTION IMMEDIATE; -- crash
INSERT INTO table (...) VALUES (...);
-- (end transaction)
That makes it in my opinion a framework bug. The database object that is internally handled there should not be able to be null somewhere down the line, especially when it seems that it was not null further up in the stack.
I also think that it is possible that another hidden exception could be the root cause for this. There are a lot of try { /* do stuff */ } finally { /* clean up */ } blocks within the code and the finally part will be executed even if the try part throws an exception. Now the finally block could cause another exception and the result is AFAIK that the original exception is replaced by the new exception from the finally block.
Especially executeUpdateDelete() is like
try {
acquireAndLock(WRITE);
// actual statement execution
} finally {
releaseAndUnlock();
}
if the database is closed at that point, acquireAndLock or any code in the try part could fail and that could leave the database object at null which causes releaseAndUnlock to fail again. You should get the same stacktrace.
Apart from that, don't do empty catch blocks like catch (SQLiteException e) { /* empty */ }. Log them with ACRA if possible / you don't do that already.
This NPE appears to be from a custom ROM as the Android source code is pointing to different Methods than the ones you receive in the LogCat. What I do for such cases is that: if the rate of these exceptions is very rare, I ignore them as it is difficult to know what custom ROM is running on the phone and more difficult to get the source code of this custom ROM to know where the problem is.
Not many users are using custom ROMs, so if you extensively tested your App on different phones with different SDKs and the rate of the Exceptions you get is not that significant, you can ignore them. Otherwise, you can take a shoot in the dark and speculate what can be in this custom ROM that is causing NPE (personally, I think it is not worth the effort).
I am looking at how to handle exceptions in Android.
In the update() function in the sample code for the Notepad Content Provider, it calls getWriteableDatabase(), which can potentially throw an SQLiteException.
I notice that the NoteEditor Activity saveNote() function has the following code:
// Commit all of our changes to persistent storage. When the update completes
// the content provider will notify the cursor of the change, which will
// cause the UI to be updated.
try {
getContentResolver().update(mUri, values, null, null);
} catch (NullPointerException e) {
Log.e(TAG, e.getMessage());
}
What happens if an SQLiteException occurs?. I want to be able to catch this exception in the Activity and display an appropriate message to the user (via a toast or something similar).
I thought I could do by adding an extra catch for SQLiteException. However, I read the following info in the Google docs:
"Remember that the Android system must be able to communicate the Exception across process boundaries. Android can do this for the following exceptions that may be useful in >handling query errors:
IllegalArgumentException (You may choose to throw this if your provider receives an >invalid content URI)
NullPointerException"
So I am now confused - can I catch the SQLiteException or not?
Whenever possible, you should catch the Exception in the class or component in which the Exception occurred. Use some sort of broadcast mechanism or return value semantics to report errors across processes.
It's admittedly a tricky situation. Some people say that if an SQLite (or other Exception) occurs in a ContentProvider, the provider should propagate the exception upwards instead of returning null in the Cursor. However, this generally won't work across processes! On the other hand, returning null doesn't give you a lot of information.
A limited set of Exceptions do traverse process boundaries, but SQLiteException isn't among them - still they might be useful/appropriate.