我是应用程序开发的新手，到目前为止，我的应用程序正在按预期工作，但只有当我从Android Studio在我的设备上启动它时。例如，我有一个实例变量，我在 onCreate(( 方法中给出的值为 1。当我将应用程序从 android 工作室启动到我的设备上时，它工作正常，变量的值为 1。但是，当我在不使用 android 工作室的情况下从我的设备启动它时，该变量的值为 0。我还发现我会在我知道应该有一个值的变量上得到一堆 NullPointerExceptions，并且当从 Android Studio 启动时它再次有效，但在从设备启动时则不然。
这是主要活动
public class MainActivity extends AppCompatActivity
{
private ArrayList<String> arrayList;
private ArrayList<ListItem> itemList;
private ArrayAdapter<String> adapter;
private EditText txtInput;
private int payRoll;
private String value;
private Intent mainToPayroll;
private int hours;
private int earnings;
private ArrayList<Integer> rollList;
private ArrayList<Integer> hourList;
private ArrayList<Integer> wageList;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
rollList = new ArrayList<>(0);
hourList = new ArrayList<>(0);
wageList = new ArrayList<>(0);
payRoll = 1;
Bundle bun = getIntent().getExtras();
if(bun != null)
{
rollList = bun.getIntegerArrayList("rolls");
hourList = bun.getIntegerArrayList("hours");
wageList = bun.getIntegerArrayList("wages");
payRoll = bun.getInt("roll");
}
ListView listView = (ListView) findViewById(R.id.listv);
String[] items = {};
arrayList = new ArrayList<>(Arrays.asList(items));
itemList = new ArrayList<>(0);
adapter = new ArrayAdapter<String>(this, R.layout.list_item, R.id.txtitem, arrayList);
listView.setAdapter(adapter);
Button btAdd = (Button) findViewById(R.id.btadd);
mainToPayroll = new Intent(this, PayrollActivity.class);
if(rollList != null)
{
for (int i = 0; i < rollList.size(); i++) {
ListItem newItem = new ListItem(rollList.get(i), hourList.get(i), wageList.get(i));
arrayList.add(newItem.toString());
itemList.add(newItem);
adapter.notifyDataSetChanged();
}
rollList.clear();
hourList.clear();
wageList.clear();
}
btAdd.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v)
{
ListItem newItem = new ListItem(payRoll, 0, 0);
arrayList.add(newItem.toString());
itemList.add(newItem);
adapter.notifyDataSetChanged();
payRoll++;
}
});
listView.setOnItemClickListener(new AdapterView.OnItemClickListener()
{
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{
value = (String)adapter.getItem(position);
ListItem item = itemList.get(position);
Bundle info = new Bundle();
info.putString("val", value);
info.putInt("hours", item.getHours());
info.putInt("wage", item.getWages());
info.putInt("pos", position);
if(itemList.size() > 0)
{
for (ListItem items : itemList)
{
rollList.add(items.getPayroll());
hourList.add(items.getHours());
wageList.add(items.getWages());
}
}
info.putIntegerArrayList("rolls", rollList);
info.putIntegerArrayList("hours", hourList);
info.putIntegerArrayList("wages", wageList);
info.putInt("roll", payRoll);
info.putBoolean("rest", restore);
mainToPayroll.putExtras(info);
startActivity(mainToPayroll);
}
});
}
每当单击列表视图上的项目时，都会启动此活动
public class PayrollActivity extends AppCompatActivity
{
private static TextView text;
private String payrollNumber;
private int payrollHrs;
private int payrollWages;
private int position;
private Intent payrollToMain;
private Button returnButton;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_payroll);
final Bundle info = getIntent().getExtras();
System.out.print(getIntent().getType());
payrollNumber = info.getString("val");
payrollHrs = info.getInt("hours");
payrollWages = info.getInt("wage");
position = info.getInt("pos");
payrollToMain = new Intent(this, MainActivity.class);
returnButton = (Button) findViewById(R.id.btnRtrn);
returnButton.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
Bundle thing = new Bundle();
thing.putIntegerArrayList("rolls", info.getIntegerArrayList("rolls"));
thing.putIntegerArrayList("hours", info.getIntegerArrayList("hours"));
thing.putIntegerArrayList("wages", info.getIntegerArrayList("wages"));
thing.putInt("roll", info.getInt("roll"));
thing.putBoolean("rest", info.getBoolean("rest"));
payrollToMain.putExtras(thing);
startActivity(payrollToMain);
}
});
text = (TextView) findViewById(R.id.title);
text.setText(payrollNumber);
}
public static void setLabelText(String val)
{
text.setText(val);
}
这是我为列表视图上的项目创建的类
public class ListItem
{
private int payroll;
private int hrs;
private int wages;
public ListItem(int roll, int hours, int wag)
{
payroll = roll;
hrs = hours;
wages = wag;
}
public int getPayroll()
{
return payroll;
}
public int getHours()
{
return hrs;
}
public int getWages()
{
return wages;
}
public void setPayroll(int roll)
{
payroll = roll;
}
public void setHrs(int hours)
{
hrs = hours;
}
public void setWages(int wage)
{
wages = wage;
}
public String toString()
{
return "Payroll " + payroll + "n" + hrs + " hoursn$" + wages;
}
我认为你的问题是你的MainActivity中的这段代码：
Bundle bun = getIntent().getExtras();
if(bun != null)
{
rollList = bun.getIntegerArrayList("rolls");
hourList = bun.getIntegerArrayList("hours");
wageList = bun.getIntegerArrayList("wages");
payRoll = bun.getInt("roll");
}
getIntent().getExtras()可能会返回一个非 nullBundle对象，但捆绑包可能没有您尝试访问的键，在这种情况下，您的所有实例变量都将设置为 null 或零表示int。
您可以通过简单地检查捆绑包中是否存在特定键并仅在存在时设置变量来解决此问题。
bun.containsKey()
或者，如果变量在从捆绑包中加载变量后为 null，则可以初始化变量。
尝试从设备完全卸载应用程序，然后重试。这有时可以解决问题。