Question

当我按下上一个按钮时，它不起任何作用。下一步按钮工作正常，但上一个按钮不显示上一张图像。我正在使用scroll view来加载图片：

- (IBAction)next{
    int arraycount = [appDelegate.articles count];
    for (int nextIndex = [pageControl currentPage]; nextIndex < arraycount; nextIndex++) {  
        if ( self.scrollView.contentOffset.x <= self.scrollView.frame.size.width ) {
            CGRect frame;
            frame.origin.x = self.scrollView.contentOffset.x +     self.scrollView.frame.size.width;
            frame.origin.y = 0;
            frame.size = self.scrollView.frame.size;
            [self.scrollView scrollRectToVisible:frame animated:YES];
            pageControlBeingUsed = YES;
        }
    }
}

-(IBAction)previousButtonAction
{
    int arraycount = [appDelegate.articles count];
    NSLog(@" arraycount : %d", arraycount);
    NSLog(@" [pageControl currentPage] : %d", [pageControl currentPage]);
    for (int nextIndex = [pageControl currentPage]; nextIndex>arraycount; nextIndex--) {
        if ( self.scrollView.contentOffset.x >= self.scrollView.frame.size.width ) {
            CGRect frame;
            frame.origin.x = self.scrollView.contentOffset.x + self.scrollView.frame.size.width;
            frame.origin.y = 0;
            frame.size = self.scrollView.frame.size;
            [self.scrollView scrollRectToVisible:frame animated:YES];
            pageControlBeingUsed = YES;
        }
    } 
}

Answer 1

好的，我现在认为我会采用不同的方法。我会在重新分配它之前检查当前的偏移量。

未经测试的代码：

- (IBAction)next{
    if ( self.scrollView.contentOffset.x <= self.scrollView.frame.size.width ) {
        CGRect frame;
        frame.origin.x = self.scrollView.contentOffset.x + self.scrollView.frame.size.width;
        frame.origin.y = 0;
        frame.size = self.scrollView.frame.size;
        [self.scrollView scrollRectToVisible:frame animated:YES];
        pageControlBeingUsed = YES;
    }
}

Answer 2

当用户到达第三张图片时，我会禁用“下一步”按钮。如果您希望在用户按下第三张图像中的“下一张”时返回第一张图像，则必须在if后添加其他图像以表示该情况：

- (IBAction)next{
int arraycount = [appDelegate.articles count];
for (int nextIndex = [pageControl currentPage]; nextIndex < arraycount; nextIndex++) {      
     if (nextIndex < arraycount) {
         CGRect frame;
         frame.origin.x = self.scrollView.frame.size.width * nextIndex;
         frame.origin.y = 0;
         frame.size = self.scrollView.frame.size;
         [self.scrollView scrollRectToVisible:frame animated:YES];
          pageControlBeingUsed = YES;
      }
      // If the user clicks on next in the last item, return to the first
      else {
         CGRect frame;
         frame.origin.x = 0;
         frame.origin.y = 0;
         frame.size = self.scrollView.frame.size;
         [self.scrollView scrollRectToVisible:frame animated:YES];
          pageControlBeingUsed = YES;
      }
  }

}

Answer 3

arraycount = 3

[pageControl currentPage]为零索引，因此当您在第3页时它等于2.

所以你的for循环nextIndex的开始等于2，小于arrayCount，所以它进入你的循环。

将其更改为：

for (int nextIndex = [pageControl currentPage]; nextIndex < (arraycount-1); nextIndex++) {

好的是这个输出：

- (IBAction)next{
    int arraycount = [appDelegate.articles count];
NSLog(@" arraycount : %d", arraycount);
NSLog(@" [pageControl currentPage] : %d", [pageControl currentPage]);
    for (int nextIndex = [pageControl currentPage]; nextIndex < (arraycount-1); nextIndex++) {
NSLog(@" nextIndex : %d", nextIndex);
         CGRect frame;
         frame.origin.x = self.scrollView.frame.size.width * nextIndex;
         frame.origin.y = 0;
         frame.size = self.scrollView.frame.size;
         [self.scrollView scrollRectToVisible:frame animated:YES];
          pageControlBeingUsed = YES;

      }
}

Answer 4

对我说它在swift 3中工作。

 func prevAction (sender:UIButton)
{
    print("self.scView.contentOffset.x ..\(self.scView.contentOffset.x)")
    if ( self.scView.contentOffset.x <= self.scView.contentSize.width )
    {
        var frame = CGRect()

        frame.origin.x = self.scView.contentOffset.x - 80;
        frame.origin.y = 0;
        frame.size = self.scView.frame.size;

        self.scView .scrollRectToVisible(frame, animated: true)

    }


}

感谢@ader。

使用按钮单击在ScrollView中移动上一个图像

4 个答案: