Java中的分页

问题描述

我写了分页逻辑：

我的要求：要显示的总元素：每页100个，如果我点击下一个它应该显示接下来的100个记录，如果我点击上一个100条记录。

My requirement: total elements to display:100 per page,if i click next it should display next 100 records,if i click previous 100 records.

初始可变值：

• showFrom：1，


• showTo：100


• 最大元素：取决于数据大小。


• pageSize：100。

• showFrom:1,
• showTo:100
• max elements:depends on size of data.
• pageSize:100.

代码：

if(paging.getAction().equalsIgnoreCase("Next")){
  paging.setTotalRec(availableList.size());
  showFrom = (showTo + 1);
  showTo = showFrom + 100- 1;
  if(showTo >= paging.getTotalRec())
    showTo = paging.getTotalRec();
  paging.setShowFrom(showFrom);
  paging.setShowTo(showTo);
}

else if(paging.getAction().equalsIgnoreCase("Previous")){
  showTo = showFrom - 1;
  showFrom = (showFrom - 100);
  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());
}

在这里，我可以删除元素并将其添加到现有数据。上面的代码可以正常工作很好，如果我添加和删除一些元素。但如果我一次删除或添加100个元素计数不正确显示上面的代码工作正常，如果我添加和删除一些元素。

Here i can remove and add the elements to the existing data.above code works fine if i add and remove few elements.but if i remove or add 100 elements at a time counts are not displaying properly above code works fine if i add and remove few elements.

推荐答案

要改进的一些事项：

• 用<$ c替换magic值100 $ c> final int PAGE_SIZE = 100;


• 将冗余代码分解出来。

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
  paging.setTotalRec(availableList.size());

到if / else之外以使你的逻辑更清晰

to outside of if/else to make your logic clearer

• 确保前一个> = 0且下一个< =记录数

修改：

final int PAGE_SIZE = 100;
int numberOfPages = -1;
int currentPage = -1;

public void initializeVariables(){
  paging.setTotalRec(availableList.size());
  showFrom = 1; 
  showTo = PAGE_SIZE;
  //keep track of how many pages there should be
  numberOfPages = paging.getTotalRec()/PAGE_SIZE;
  currentPage = 1;
}

public void handlePagingAction(){
  if(paging.getAction().equalsIgnoreCase("Next")){
     if(currentPage < numberOfPages){
        ++currentPage;
     }
  }else if(paging.getAction().equalsIgnoreCase("Previous")){
     if(currentPage > 1){       
       --currentPage;
     }
  }      

  showFrom = (currentPage - 1) * PAGE_SIZE + 1;
  if(showFrom < 0){
    showFrom = 0
  }

  showTo = currentPage * PAGE_SIZE;
  if(showTo >= paging.getTotalRec()){
    showTo = paging.getTotalRec();
  }     

  paging.setShowTo(showTo);
  paging.setShowFrom(showFrom);
}

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