Method `writeToFile:atomically:` **ALWAYS OVERWRITE FILE**, regardless of the `atomically:` YES or NO.

Information from [Apple docs][1] (NSData, section &quot;Saving Data&quot;):

&gt; The NSData class and its subclasses provide methods to quickly and
&gt; easily save their contents to disk. To minimize the risk of data loss,
&gt; these methods provide the option of saving the data atomically. Atomic
&gt; writes guarantee that the data is either saved in its entirety, or it
&gt; fails completely. The atomic write begins by writing the data to a
&gt; temporary file. If this write succeeds, then the method moves the
&gt; temporary file to its final location.

No one word about checking if file exist.

For example, for method `copyItemAtPath:toPath:error:` in [docs][2] (NSFileManager, section Discussion) specifically written about such checking:

&gt; If a file with the same name already exists at dstPath, this method
&gt; stops the copy attempt and returns an appropriate error.


  [1]: https://developer.apple.com/reference/foundation/nsdata
  [2]: https://developer.apple.com/reference/foundation/nsfilemanager/1407903-copyitematpath

I&#39;m trying to write a program that looks at a .CSV file (input.csv) and rewrites only the rows that begin with a certain element (corrected.csv), as listed in a text file (output.txt).

This is what my program looks like right now:

    import csv

    lines = []
    with open(&#39;output.txt&#39;,&#39;r&#39;) as f:
        for line in f.readlines():
            lines.append(line[:-1])

    with open(&#39;corrected.csv&#39;,&#39;w&#39;) as correct:
        writer = csv.writer(correct, dialect = &#39;excel&#39;)
        with open(&#39;input.csv&#39;, &#39;r&#39;) as mycsv:
            reader = csv.reader(mycsv)
            for row in reader:
                if row[0] not in lines:
                    writer.writerow(row)

Unfortunately, I keep getting this error, and I have no clue what it&#39;s about.

    Traceback (most recent call last):
      File &quot;C:\Python32\Sample Program\csvParser.py&quot;, line 12, in &lt;module&gt;
        for row in reader:
    _csv.Error: line contains NULL byte


Credit to all the people &lt;a href=&quot;https://stackoverflow.com/questions/7853606/whats-wrong-with-this-python-program-working-on-csv/7853688#7853688&quot;&gt;here&lt;/a&gt; to even to get me to this point.

&quot;Line contains NULL byte&quot; in CSV reader (Python)

I have a class that implements `IEnumerable`, but doesn&#39;t implement `IEnumerable&lt;T&gt;`. I can&#39;t change this class, and I can&#39;t use another class instead of it. As I&#39;ve understood from MSDN [LINQ can be used if class implements `IEnumerable&lt;T&gt;`][1]. I&#39;ve tried using `instance.ToQueryable()`, but it still doesn&#39;t enable LINQ methods. I know for sure that this class can contain instances of only one type, so the class could implement `IEnumerable&lt;T&gt;`, but it just doesn&#39;t. So what can I do to query this class using LINQ expressions?


  [1]: http://msdn.microsoft.com/en-us/library/bb308959.aspx#linqoverview_topic3

Does LINQ work with IEnumerable?

Really simple question but it doesn&#39;t seem to be clear in Apple&#39;s docs.

Will `writeToFile:atomically:` for `NSData`, `NSArray` etc. overwrite existing data on a file?

Will writeToFile:atomically: overwrite data?

<p>Really simple question but it doesn't seem to be clear in Apple's docs.</p>
<p>Will <code>writeToFile:atomically:</code> for <code>NSData</code>, <code>NSArray</code> etc. overwrite existing data on a file?</p>


I&#39;m trying to make a `UIButton` that has two lines of text in its titleLabel. This is the code I&#39;m using:
    
    UIButton *titleButton = [[UIButton alloc] initWithFrame:CGRectMake(15, 10, frame.size.width-100, 100)];
    titleButton.titleLabel.font = [UIFont boldSystemFontOfSize:24.0];
    [titleButton setTitle:@&quot;This text is very long and should get truncated at the end of the second line&quot; forState:UIControlStateNormal];
    titleButton.titleLabel.lineBreakMode = UILineBreakModeTailTruncation;
    titleButton.titleLabel.numberOfLines = 2;
    [self addSubview:titleButton];

When I try this, the text only appears on one line. It seems the only way to achieve more than one line of text in `UIButton.titleLabel` is to set `numberOfLines=0` and use `UILineBreakModeWordWrap`. But this doesn&#39;t guarantee the text to be exactly two lines.

Using a plain `UILabel`, however, does work:

    UILabel *titleLabel = [[UILabel alloc] initWithFrame:CGRectMake(15, 10, frame.size.width-100, 100)];
    titleLabel.font = [UIFont boldSystemFontOfSize:24.0];
    titleLabel.text = @&quot;This text is very long and should get truncated at the end of the second line&quot;;
    titleLabel.numberOfLines = 2;
    titleLabel.lineBreakMode = UILineBreakModeTailTruncation;
    [self addSubview:titleLabel];

        

Does anyone know how to make the `UIButton` work with two lines? Is the only solution to create a separate `UILabel` to hold the text, and add it as a subview of the button?



UIButton with two lines of text in the title (numberOfLines=2)

It is my understanding that setting an ivar now retains the object being assigned to it, since setting variables defaults to the `strong` qualifier. Because ivars are in the scope of the object they are declared in and `strong` retains objects within the scope of the variable, this means the ivars value would never be released while the object containing the ivar is still alive.

Is this correct?

If so, am I right in thinking that there is, in terms of memory management, no difference between a retaining (strong) property and a simple ivar anymore?

Property vs. ivar in times of ARC

I want to check if the user is running the app on iOS less than 5.0 and display a label in the app.

How do I detect which iOS is running on user&#39;s device programmatically?

Thanks!

How can we programmatically detect which iOS version is device running on?

I have a working app and I&#39;m working on converting it to ARC in Xcode 4.2. One of the pre-check warnings involves capturing `self` strongly in a block leading to a retain cycle. I&#39;ve made a simple code sample to illustrate the issue. I believe I understand what this means but I&#39;m not sure the &quot;correct&quot; or recommended way to implement this type of scenario.

 - self is an instance of class MyAPI
 - the code below is simplified to show only the interactions with the objects and blocks relevant to my question
 - assume that MyAPI gets data from a remote source and MyDataProcessor works on that data and produces an output
 - the processor is configured with blocks to communicate progress &amp; state

code sample:

    // code sample
    self.delegate = aDelegate;
    
    self.dataProcessor = [[MyDataProcessor alloc] init];
    
    self.dataProcessor.progress = ^(CGFloat percentComplete) {
        [self.delegate myAPI:self isProcessingWithProgress:percentComplete];
    };
    
    self.dataProcessor.completion = ^{
        [self.delegate myAPIDidFinish:self];
        self.dataProcessor = nil;
    };
    
    // start the processor - processing happens asynchronously and the processor is released in the completion block
    [self.dataProcessor startProcessing];

Question: what am I doing &quot;wrong&quot; and/or how should this be modified to conform to ARC conventions?

How do I avoid capturing self in blocks when implementing an API?

How can I check if a file exists at a URL (instead of a path), in order to set a pre-populated default store into the iPhone Simulator: 

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@&quot;Food.sqlite&quot;];
    /*
	 Set up the store.
	 For the sake of illustration, provide a pre-populated default store.
	 */
	NSFileManager *fileManager = [NSFileManager defaultManager];
	// If the expected store doesn&#39;t exist, copy the default store.
	if (![fileManager fileExistsAtPath:storePath]) {
		NSString *defaultStorePath = [[NSBundle mainBundle] pathForResource:@&quot;Food&quot; ofType:@&quot;sqlite&quot;];
		if (defaultStorePath) {
			[fileManager copyItemAtPath:defaultStorePath toPath:storePath error:NULL];
		}
	}

  
I&#39;ve read that in recent versions of the templates, the applicationDocumentsDirectory method returns an URL, so I&#39;ve changed the code to use NSURL objects to represent the file path. But at `[fileManager fileExistsAtPath:storePath]`, I need to change `fileExistsAtPath` to something like `fileExistsAtURL` (obviously it doesn&#39;t exist).

I&#39;ve checked the NSFileManager Class Reference and I didn&#39;t find any suitable task suited for my purpose.

Any hints please?

Check if file exists at URL instead of path

Is there a way to insert a Table Header View (tableHeaderView) in StoryBoard (like we used to do in Interface Builder)?

Table Header Views in StoryBoards

I have a problem with Xcode 4.2 debugging in an iOS 5 simulator/device. The following code crashes, as expected:

    NSArray *arr=[NSArray array];
    [arr objectAtIndex:100];

In iOS 4, I get a useful stack trace of hex numbers. But in iOS 5, it just gives me:

    *** First throw call stack:
    (0x16b4052 0x1845d0a 0x16a0674 0x294c 0x6f89d6 0x6f98a6 0x708743 0x7091f8 0x7fcaa9 0x2257fa9 0x16881c5 0x15ed022 0x15eb90a 0x15eadb4 0x15eaccb 0x6f02a7 0x6faa93 0x2889 0x2805)

Thanks.

Content Type	Original Author	Original Content on Stackoverflow
Question	Jiho Kang	View Question on Stackoverflow
Solution 1 - Objective C	BJ Homer	View Answer on Stackoverflow
Solution 2 - Objective C	Igor	View Answer on Stackoverflow

Will writeToFile:atomically: overwrite data?

Objective C Problem Overview

Objective C Solutions

Solution 1 - Objective C

Solution 2 - Objective C

Does LINQ work with IEnumerable?

"Line contains NULL byte" in CSV reader (Python)

Attributions