寫程式與除錯，最簡單來檢查有無錯誤的方式，就是看Log，把想要知道的狀態給「列印」到控制台。
現在的需求是想知道用戶陸續做了什麼動作，我們也能透過Log來得知一二。
那麼如何在本機端建立Log檔案呢？其實就只是字串的處理，開檔、寫檔、關檔，原本我想要土法煉鋼，每次都讀取整個檔，陸續把Log寫到檔案最後面，最後覆蓋原檔儲存。
上述做法是可以做到，不過就會考量到萬一檔案大到好幾MB，讀取時間肯定會越來越長。想要解決這個議題，就想到我寫C/C++時的做法⋯⋯
我試著建立三個按鈕，分別為寫檔、讀檔、清除，讀檔會將MyHappyLog.txt字串讀出，並在TextView顯示。
其實過去可以透過iTunes將手機App的檔案拉到電腦中查看，現在10.15.5作業系統Finder有相似的功能。
程式碼大致上如此：
/**
Theme: Create Log File
IDE: Xcode 11
Language: Objective C
Date: 108/06/01
Author: HappyMan
Blog: https://cg2010studio.com/
*/
-(IBAction)aButtonClicked:(UIButton *)button
{
NSString *content = @"I am Happy and Lucky\n";
// Get the file path
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"MyHappyLog.txt"];
// Create file if it doesn't exist
if(![[NSFileManager defaultManager] fileExistsAtPath:fileName])
[[NSFileManager defaultManager] createFileAtPath:fileName contents:nil attributes:nil];
// Append text to file (you'll probably want to add a newline every write)
NSFileHandle *file = [NSFileHandle fileHandleForUpdatingAtPath:fileName];
[file seekToEndOfFile];
[file writeData:[content dataUsingEncoding:NSUTF8StringEncoding]];
[file closeFile];
}
-(IBAction)bButtonClicked:(UIButton *)button
{
// Get file path
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"MyHappyLog.txt"];
// Read the whole file as a single string
NSString *content = [NSString stringWithContentsOfFile:fileName encoding:NSUTF8StringEncoding error:nil];
self.aTextView.text = content;
}
-(IBAction)cButtonClicked:(UIButton *)button
{
// Get file path
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *fileName = [documentsDirectory stringByAppendingPathComponent:@"MyHappyLog.txt"];
// Clear file
NSError *error;
[@"" writeToFile:fileName atomically:YES encoding:NSUTF8StringEncoding error:&error];
}
接著在各個重要事件寫入對應的字串，並等設計師把畫面設計出來，可請用戶點擊某按鈕上傳Log檔。
逍遙文工作室 
隨意留個言吧：）～