安卓 Java HashMap在循环迭代中丢失值
我正在尝试按字母顺序重新排列地图列表。我可以看到“name”字符串被适当的值填充,但是groupDataCopy从未更新过。据我所知,使用新操作符并调用“put”将把值放入映射中。但我可以在下面的迭代中看到,ArrayList包含:
{name = null}
我不知道为什么我在地图列表中丢失了值。代码如下:
private void sortByName() {
List<Map<String, String>> groupDataCopy = new ArrayList<Map<String, String>>();
List<List<Map<String, String>>> childDataCopy = new ArrayList<List<Map<String, String>>>();
int groupPos = 0;
int nextNamePos = 0;
String name = null;
while(groupPos<groupData.size()) {
//main loop
int groupDataComparison = 0;
name = null;
while(groupDataComparison<groupData.size()) {
//comparison traversal for group
if(!groupDataCopy.isEmpty()) { //if groupDataCopy has data
if(groupDataCopy.get(groupDataCopy.size()-1).get("name").compareTo(groupData.get(groupDataComparison).get("name")) > 0) { //if the last index of groupDataCopy is alphabetically after (or equal to) last chosen name
if(name==null || groupData.get(groupDataComparison).get("name").compareTo(name) < 0) {
name = groupData.get(groupDataComparison).get("name");
nextNamePos = groupDataComparison;
}
}
} else {
if(name==null || groupData.get(groupDataComparison).get("name").compareTo(name) < 0) {
name = groupData.get(groupDataComparison).get("name");
nextNamePos = groupDataComparison;
}
}
groupDataComparison++;
}
groupDataCopy.add(new HashMap<String, String>());
groupDataCopy.get(groupPos).put("name", name);
childDataCopy.add(new ArrayList<Map<String, String>>());
for(Map<String, String> data : childData.get(nextNamePos)) {
childDataCopy.get(groupPos).add(data);
}
groupPos++;
}
groupData = groupDataCopy;
childData = childDataCopy;
}
# 1 楼答案
# 2 楼答案
尝试创建一个可以使用集合的比较器。排序:
比如:
之后,你可以简单地做: