Question

String[] m_cPackageName;

int m_size;

int j=0;

List<ApplicationInfo> installedList = packageManager.getInstalledApplications(PackageManager.GET_META_DATA);
m_size = installedList.size();

m_cPackageName=new String[m_size];

for (PackageInfo pi : pkginfoList) {

    try {
        m_appinfo = packageManager.getApplicationInfo(pi.packageName, 0);
        if ((m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
        // equal to zoo means system apps, not equal is third party installed apps 
        m_cPackageName[j]=pi.packageName;

        j++;
        }
    } catch (NameNotFoundException e) {
        Log.d(getClass().getSimpleName(), "Name not found", e);
}

这里我得到的instalList的总大小是56 ..在数组中填充值后，它显示为空值。我怎样才能消除空值..对我来说任何一个帮助..

输出：

m_cPackageName=String[56];

m_cPackageName[0]="Myvalue"

m_cPackageName[1]="null"

m_cPackageName[2]="null"
.

.

.

m_cPackageName[55]="null"

Answer 1

在将元素插入数组之前添加空检查。

if ((m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
   if(pi.packageName!=null){
        m_cPackageName[j]=pi.packageName;
        j++;
   }
}

Answer 2

  if (((m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0)&& (pi.packageName != null &&!pi.packageName.equals("")) {
                         // equal to zoo means system apps, not equal is third party installed apps 
                          m_cPackageName[j]=pi.packageName;

                            j++;
                       }

Answer 3

您正在根据installedList的大小分配数组，但是您正在迭代pkginfoList。更好的方法是创建List<String> packageNames = new ArrayList<String>();，然后在循环中添加到该列表。

这样，您不必担心计数或尺寸。

Answer 4

if ((m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
  // equal to zoo means system apps, not equal is third party installed apps 
    if(pi.packageName!=null){
        m_cPackageName[j]=pi.packageName;
        j++;
     }
 }

Answer 5

小于m_size个元素被添加到数组（大小为m_size），最终导致未分配的null个元素。

这是因为 j有时只会增加 - 在条件（(m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0）内，并且只有在没有抛出并捕获异常时才会增加。

一个简单的解决方案是使用ArrayList，然后只添加“已批准”元素。因为List / ArrayList按需增长，所以在固定大小的数组中没有可以找到的尾随空（未分配）元素。

// List, not array
List<String> m_cPackageName = new ArrayList<String>();

// ..
if ((m_appinfo.flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
    // Only added to list sometimes, but m_cPackageName.size() is
    // always the count of elements that HAVE been added.
    m_cPackageName.add(pi.packageName);
}

// Then, if you really need an array, which will now be the proper size
// and not contain null elements because the size is computed based on the
// accepted elements in m_cPackageName which is m_cPackageName.size() ..
String[] arrayOfPackageNames = m_cPackageName.toArray(new String[0]);

Answer 6

如果您不需要消除空字符串和空字符串的歧义，请考虑将空值存储为空;像这样的东西：

m_cPackageName[j]=pi.packageName == null ? "" : pi.packageName;

这可能会降低因NullPointerException-s进一步下降而导致事件爆发的风险。

如何避免java中String数组中的空值？

6 个答案: