iphone - 从 iphone 真实设备拍摄的图片在 iphone 中以缩略图显示的图像花费的时间太长

Question

我是手机编程的新手。我将图像存储在数组中，然后使用下面的代码我以缩略图显示图像，它的工作速度非常快。如果同样认为我将图像存储在数据库中并检索图像并存储在数组中，然后使用在下面的代码中，我正在以缩略图形式显示图像，但显示缩略图图像所花费的时间太长。

  arrayz = [NSMutableArray arrayWithObjects:[UIImage imageNamed:@"image3.jpg"],
             [UIImage imageNamed:@"image4.jpg"],
             [UIImage imageNamed:@"image5.jpg"],
             [UIImage imageNamed:@"image3.jpg"],

             [UIImage imageNamed:@"image5.jpg"],
             [UIImage imageNamed:@"image4.jpg"],
             [UIImage imageNamed:@"image2.jpg"],
             [UIImage imageNamed:@"image3.jpg"],
             [UIImage imageNamed:@"image2.jpg"],
             [UIImage imageNamed:@"image5.jpg"],

             nil];

    NSLog(@"%i" , [arrayz count]);
    NSLog(@"%@",arrayz);

    myScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0.0, 0.0, 320.0, 840.0)];
    myScrollView.delegate = self;
    myScrollView.contentSize = CGSizeMake(320.0, 840.0);
    myScrollView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:myScrollView];

    float horizontal = 8.0;
    float vertical = 8.0;

    for(int i=0; i<[arrayz count]; i++)
    {
        if((i%4) == 0 && i!=0)
        {
            horizontal = 8.0;
            vertical = vertical + 70.0 + 8.0;
        }
        buttonImage1 = [UIButton buttonWithType:UIButtonTypeCustom];
        [buttonImage1 setFrame:CGRectMake(horizontal, vertical, 70.0, 70.0)];
        [buttonImage1 setTag:i];

        [buttonImage1 setImage:[arrayz objectAtIndex:i] forState:UIControlStateNormal];
        [buttonImage1 addTarget:self action:@selector(buttonImagePressed:) forControlEvents:UIControlEventTouchUpInside];
        [buttonImage1 setImage:[UIImage imageNamed:@"Overlay.png"] forState:UIControlStateSelected];
        buttonImage = [UIButton buttonWithType:UIButtonTypeCustom];
        [buttonImage setFrame:CGRectMake(horizontal, vertical, 70.0, 70.0)];
        [buttonImage setTag:i];

        [buttonImage setImage:[arrayz objectAtIndex:i] forState:UIControlStateNormal];
        [buttonImage addTarget:self action:@selector(buttonImagePressed:) forControlEvents:UIControlEventTouchUpInside];
        [buttonImage setImage:[UIImage imageNamed:@"Overlay.png"] forState:UIControlStateSelected];

        // UIImageView *imageee=[[UIImageView alloc]initWithFrame:CGRectMake(10,10, 80,80)];
        // [buttonImage setImage:[UIImage imageNamed:@"check.jpg"]];

        // [buttonImage setImage:imageee forState:UIControlStateSelected];
        // [buttonImage setImage:button.currentImage forState:UIControlStateNormal];



        [myScrollView addSubview:buttonImage1];
        [myScrollView addSubview:buttonImage];

        horizontal = horizontal + 70.0 + 8.0;
          [myScrollView setContentSize:CGSizeMake(320.0, vertical + 78.0)];
        }



    // Do any additional setup after loading the view, typically from a nib.
    self.navigationItem.leftBarButtonItem = self.editButtonItem;
    //  UIBarButtonItem *done =[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonItemStyleDone target:self action:nil];
    UIBarButtonItem *done = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(insertNewObject:)];
    self.navigationItem.rightBarButtonItem = done;

下面的代码使用数据库，我将图像存储在数组中，然后我以缩略图形式显示图像。以缩略图形式显示图像花费的时间太长。

    NSString *docsDir;
    NSArray *dirPaths;

    // Get the documents directory
    dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    docsDir = [dirPaths objectAtIndex:0];
    array=[[NSMutableArray alloc]init];
    array1=[[NSMutableArray alloc]init];
    // array2=[[NSMutableArray alloc]init];


    // Build the path to the database file
    databasePath =  [docsDir stringByAppendingPathComponent: @"Taukydataaa.db"];
    //  NSLog(@"%@",databasePath);
    NSFileManager *fn=[NSFileManager defaultManager];
    NSError *error;
    BOOL success=[fn fileExistsAtPath:databasePath];

    if(!success) {

        NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Taukydataaa.db"];
        success = [fn copyItemAtPath:defaultDBPath toPath:databasePath error:&error];
    }


    const char *dbpath = [databasePath UTF8String];

    sqlite3_stmt    *statement;

    if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK)
    {

      NSString *querySQL = [NSString stringWithFormat: @"select * from path "];

        const char *query_stmt = [querySQL UTF8String];

        if (sqlite3_prepare_v2(contactDB, query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
            while(sqlite3_step(statement) == SQLITE_ROW)
            {

                NSString* email_idField = [[NSString alloc] initWithUTF8String:(const char *) sqlite3_column_text(statement,1)];
                //   NSLog(@"%@",email_idField);
                NSString* email_idField1 = [[NSString alloc] initWithUTF8String:(const char *) sqlite3_column_text(statement,0)];
                // NSLog(@"%@",email_idField1);

                //       NSString *email_idField2 = [[NSString alloc] initWithUTF8String:(const char *) sqlite3_column_text(statement,2)];
                NSLog(@"ASlma");

                NSLog(@"%@",email_idField1);
                [array addObject:email_idField];
                [array1 addObject:email_idField1];
                NSLog(@"%@",array);
                NSLog(@"%@",array1);
                //  [array1 addObject:email_idField1];
                //   [array2 addObject:email_idField2];



            }
            sqlite3_finalize(statement);
        }
        sqlite3_close(contactDB);

    }
    blaukypath =[[NSMutableArray alloc]init];
    for (NSString* path in array)
    {
        [blaukypath addObject:[UIImage imageWithContentsOfFile:path]];
        NSLog(@"%@",path);
    }
    NSLog(@"%@",blaukypath1);


    myScrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0.0, 0.0, 320.0, 840.0)];
    myScrollView.delegate = self;
    myScrollView.contentSize = CGSizeMake(320.0, 840.0);
    myScrollView.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:myScrollView];

    float horizontal = 8.0;
    float vertical = 8.0;

    for(int i=0; i<[blaukypath count]; i++)
    {
        if((i%4) == 0 && i!=0)
        {
            horizontal = 8.0;
            vertical = vertical + 70.0 + 8.0;
        }
        buttonImage1 = [UIButton buttonWithType:UIButtonTypeCustom];
        [buttonImage1 setFrame:CGRectMake(horizontal, vertical, 70.0, 70.0)];
        [buttonImage1 setTag:i];

        [buttonImage1 setImage:[blaukypath objectAtIndex:i] forState:UIControlStateNormal];
        [buttonImage1 addTarget:self action:@selector(buttonImagePressed:) forControlEvents:UIControlEventTouchUpInside];
        [buttonImage1 setImage:[UIImage imageNamed:@"Overlay.png"] forState:UIControlStateSelected];
        buttonImage = [UIButton buttonWithType:UIButtonTypeCustom];
        [buttonImage setFrame:CGRectMake(horizontal, vertical, 70.0, 70.0)];
        [buttonImage setTag:i];

        [buttonImage setImage:[blaukypath objectAtIndex:i] forState:UIControlStateNormal];
        [buttonImage addTarget:self action:@selector(buttonImagePressed:) forControlEvents:UIControlEventTouchUpInside];
        [buttonImage setImage:[UIImage imageNamed:@"Overlay.png"] forState:UIControlStateSelected];

        // UIImageView *imageee=[[UIImageView alloc]initWithFrame:CGRectMake(10,10, 80,80)];
        // [buttonImage setImage:[UIImage imageNamed:@"check.jpg"]];

        // [buttonImage setImage:imageee forState:UIControlStateSelected];
        // [buttonImage setImage:button.currentImage forState:UIControlStateNormal];



        [myScrollView addSubview:buttonImage1];
        [myScrollView addSubview:buttonImage];

        horizontal = horizontal + 70.0 + 8.0;
          [myScrollView setContentSize:CGSizeMake(320.0, vertical + 78.0)];
        }

我认为问题不在于数据库。主要的想法是，如果我从我的手机真实设备拍摄图像，这些图像花费的时间太长而无法以缩略图显示。如果我拍摄一些图像并将其存储在数组中，那么图像以缩略图显示它的工作非常快..任何人都可以告诉我如何解决这个问题。谢谢阿斯拉姆

Answer 1

真实图像的尺寸更大，因此最好在使用前调整它们的大小。试试这个

UIImage *originalImage = your orginal Image
CGSize destinationSize = CGSizeMake(100, 120);// your destination thumbnail size

UIGraphicsBeginImageContext(destinationSize);
[originalImage drawInRect:CGRectMake(0,0,destinationSize.width,destinationSize.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();