问题
I'm running a very basic test App with Instruments, and it finds a lot of memory leaks! Since I know that Apple guys perform checks for leaked memory when an App is submitted to iTunes, I would like to investigate the problem.
My environment: MonoDevelop 2.4.2 with MonoTouch 3.2.4 on Mac OS X 10.6.6, targeting an iPad running iOS 4.2.1.
My test App simply shows a TableView populated with a list of 50 strings, grouping them by their starting letter.
Steps to reproduce the problem: create a new "iPad Window-based Project" with MonoDevelop, open the MainWindow.xib file with Interface Builder, place a new TableView onto the window and create its outlet (named "tview") to the AppDelegate class. Then enter the following code in Main.cs:
using System;
using System.Collections.Generic;
using System.Linq;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
namespace SimpleTable
{
public class Application
{
static void Main (string[] args)
{
UIApplication.Main (args);
}
}
public partial class AppDelegate : UIApplicationDelegate
{
private List<string> _names;
public override bool FinishedLaunching (UIApplication app, NSDictionary options)
{
_names = new List<string> { "Smith", "Jones", "Williams", "Brown", "Taylor",
"Davies", "Wilson", "Evans", "Thomas", "Johnson",
"Roberts", "Walker", "Wright", "Robinson", "Thompson",
"White", "Hughes", "Edwards", "Green", "Hall",
"Wood", "Harris", "Lewis", "Martin", "Jackson",
"Clarke", "Clark", "Turner", "Hill", "Scott",
"Cooper", "Morris", "Ward", "Moore", "King",
"Watson", "Baker", "Harrison", "Morgan", "Patel",
"Young", "Allen", "Mitchell", "James", "Anderson",
"Phillips", "Lee", "Bell", "Parker", "Davis" };
tview.Source = new MyTableViewSource(_names);
window.MakeKeyAndVisible ();
return true;
}
private class MyTableViewSource : UITableViewSource
{
private List<string> _sectionTitles;
private SortedDictionary<int, List<string>> _sectionElements = new SortedDictionary<int, List<string>>();
public MyTableViewSource(List<string> list)
{
// Use LINQ to find the distinct set of alphabet characters required.
_sectionTitles = (from c in list select c.Substring(0, 1)).Distinct().ToList();
// Sort the list alphabetically.
_sectionTitles.Sort();
// Add each element to the List<string> according to the letter it starts with
// in the SortedDictionary<int, List<string>>.
foreach (string element in list)
{
int sectionNum = _sectionTitles.IndexOf(element.Substring(0, 1));
if (_sectionElements.ContainsKey(sectionNum))
{
// SortedDictionary already contains a List<string> for that letter.
_sectionElements[sectionNum].Add(element);
}
else
{
// First time that letter has appeared, create new List<string> in the SortedDictionary.
_sectionElements.Add(sectionNum, new List<string> { element });
}
}
}
public override int NumberOfSections(UITableView tableView)
{
return _sectionTitles.Count;
}
public override string TitleForHeader(UITableView tableView, int section)
{
return _sectionTitles[section];
}
public override int RowsInSection(UITableView tableview, int section)
{
return _sectionElements[section].Count;
}
public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
{
string kCellIdentifier = "mycell";
UITableViewCell cell = tableView.DequeueReusableCell(kCellIdentifier);
if (cell == null)
{
// No re-usable cell found, create a new one.
cell = new UITableViewCell(UITableViewCellStyle.Default, kCellIdentifier);
}
string display = _sectionElements[indexPath.Section][indexPath.Row];
cell.TextLabel.Text = display;
return cell;
}
public override void RowSelected(UITableView tableView, NSIndexPath indexPath)
{
string display = _sectionElements[indexPath.Section][indexPath.Row];
showAlert("RowSelected", "You selected: \"" + display + "\"");
// Prevent the blue 'selection indicator' remaining.
tableView.DeselectRow(indexPath, true);
}
private void showAlert(string title, string message)
{
using (var alert = new UIAlertView(title, message, null, "OK", null))
{
alert.Show();
}
}
}
}
}
I have performed the following tests on the device:
commented out
public override string TitleForHeader(UITableView tableView, int section)procedure, launched App from within Instruments: a single leak is found; it seems that this leak is ALWAYS present, even when testing an empty App!
Test 1 Instruments screenshot
uncommented
public override string TitleForHeader(UITableView tableView, int section)procedure, launched App from within Instruments: a lot of leaks are found, and their number grows up when scrolling the table up and down and/or selecting any row.
Test 2 Instruments screenshot
substituted the
return _sectionTitles[section];statement in
public override string TitleForHeader(UITableView tableView, int section)procedure with
return "Test Header…";(thus using a constant string): the same as in test n.2!
Is MonoTouch bugged or am I forgetting something essential? If even such a simple App generates hundreds of memory leaks when running for a few minutes, what could happen with a real (and more complex) App?
I have searched the web extensively but I haven't found any significant post about this problem... any contribution will be greatly appreciated.
回答1:
The way monotouch and the mono vm allocates and manages memory isn't fully understood by instruments. Apple has not rejected any applications for this. If you have a specific bug that you think is a leak please file an issue in the monotouch bugtracker at http://monotouch.net/Support
That being said, I looked at your screenshots and did find 1 16-byte leak that could happen, and the leak in your second screenshot, and fixed that for the upcoming monotouch 4.
来源：https://stackoverflow.com/questions/5003419/why-does-monotouch-cause-lots-of-memory-leaks-as-reported-by-instruments-even