java Activity 在 setAdapter(ArrayAdapter) 上崩溃；
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原文地址: http://stackoverflow.com/questions/7489454/
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Activity crashes on setAdapter(ArrayAdapter);
提问by Fraser
Attempting to write my first ArrayAdapter for Android, failing miserably at the moment. It crashes on the setAdapter(adapter);line and throws a NullPointerException.
试图为 Android 编写我的第一个 ArrayAdapter，目前很失败。它setAdapter(adapter);在线路上崩溃并抛出 NullPointerException。
ContractTestActivity:
合同测试活动：
public class ContractTestActivity extends Activity {
private ArrayList<Contract> contracts;
public final String TAG = "ContractTest";
//public Contract newContract = new Contract();
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView list;
list = (ListView)findViewById(R.id.list);
ArrayAdapter<Contract> adapter = new ContractAdapter(this, android.R.layout.simple_list_item_1, contracts);
list.setAdapter(adapter);
}
}
ContractAdapter:
合约适配器：
public class ContractAdapter extends ArrayAdapter<Contract> {
private ArrayList<Contract> contracts;
public ContractAdapter(Context context, int view, ArrayList<Contract> passedContracts) {
super(context, view, passedContracts);
contracts = passedContracts;
}
@Override
public int getCount() {
return contracts.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View currentView = convertView;
LayoutInflater currentViewInflater = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
currentView = currentViewInflater.inflate(android.R.layout.simple_list_item_1, null);
Contract currentContract = contracts.get(position);
TextView text = (TextView) currentView.findViewById(android.R.id.text1);
text.setText(currentContract.getName());
return currentView;
}
}
Contract:
合同：
public class Contract extends ContractTestActivity {
private String name;
private float payRate;
private int hoursWorked;
private int holidays;
public Contract() {
}
public String getName() {
return name;
}
}
Suggestions?
建议？
采纳答案by Lalit Poptani
The problem is that you are not initializing your ArrayList
问题是你没有初始化你的 ArrayList
private ArrayList<Contract> contracts;
Its therefore you are getting the error NullPointerException.
因此，您收到错误 NullPointerException。
UPADATED:
更新：
ContractTestActivity.java
合约测试活动.java
public class ContractTestActivity extends Activity {
private List<Contract> contracts = new ArrayList<Contract>();
public final String TAG = "ContractTest";
//public Contract newContract = new Contract();
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView list;
list = (ListView)findViewById(R.id.mylist);
ArrayAdapter<Contract> adapter = new ContractAdapter(this, android.R.layout.simple_list_item_1, myContracts());
list.setAdapter(adapter);
}
private List<Contract> myContracts(){
List<Contract> list = new ArrayList<Contract>();
list.add(new Contract("Friend1"));
list.add(new Contract("Friend2"));
list.add(new Contract("Friend3"));
list.add(new Contract("Friend4"));
return list;
}
}
Contract.java
合同.java
public class Contract {
private String name;
public Contract(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
ContractAdapter.java
合约适配器
public class ContractAdapter extends ArrayAdapter<Contract> {
private List<Contract> contracts;
public ContractAdapter(Context context, int view, List<Contract> passedContracts) {
super(context, view, passedContracts);
contracts = passedContracts;
}
@Override
public int getCount() {
return contracts.size();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View currentView = convertView;
LayoutInflater currentViewInflater = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
currentView = currentViewInflater.inflate(android.R.layout.simple_list_item_1, null);
Contract currentContract = contracts.get(position);
TextView text = (TextView) currentView.findViewById(android.R.id.text1);
text.setText(currentContract.getName());
return currentView;
}
}
回答by Venky
Problem is that your are not adding any values to your ArrayList contracts
问题是您没有向 ArrayList 合同添加任何值
ArrayAdapter<Contract> adapter = new ContractAdapter(this, android.R.layout.simple_list_item_1, contracts);
Before this line you should add some values to contracts
在此行之前，您应该为合同添加一些值
So add values to List like this
所以像这样向 List 添加值
contracts = new ArrayList<Contract>();
contracts.add(new Contract("name"));
ArrayAdapter<Contract> adapter = new ContractAdapter(this,android.R.layout.simple_list_item_1, contracts);
Now Size of contracts will returns the Length of ArrayList.
现在合约的大小将返回 ArrayList 的长度。
回答by greeshma
Create a listview in main.xml and a text view in listview.xml
在 main.xml 中创建一个列表视图，在 listview.xml 中创建一个文本视图
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
t=(EditText)findViewById(R.id.editText1);
lv=(ListView)findViewById(R.id.listView1);
listItems = new ArrayList<String>();
dataAdapter = new ArrayAdapter<String>(this, R.layout.listview,R.id.row);
//row is id of textview
lv.setAdapter(dataAdapter);
}
In buttons click event
在按钮点击事件
dataAdapter.add(t.getText().toString());
dataAdapter.notifyDataSetChanged();
so that when the button is clicked content of edittext will be added to list view
这样当按钮被点击时，edittext 的内容将被添加到列表视图中
回答by Arpit Garg
private ArrayList contracts = ???
私有 ArrayList 合同 = ???
It should be assigned some value... or simply a null as below:
它应该被分配一些值......或者只是一个空值，如下所示：
contracts = new ArrayList<Contract>;
contracts = new ArrayList<Contract>;
Also try to String[] names = new String[] { "Linux", "Windows7", "Eclipse", "Suse",
"Ubuntu", "Solaris", "Android", "iPhone"};
// Create an ArrayAdapter, that will actually make the Strings above
// appear in the ListView
list.setAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, names));
If the exception persists... Then check the Id of the list view in xml.
如果异常仍然存在...然后检查 xml 中列表视图的 Id。
This may be due to that only.
这可能只是由于这一点。
回答by roman
ArrayAdapter<Contract> adapter = new ContractAdapter(this, android.R.layout.simple_list_item_1, contracts);
is contracts not set at this point ?
合同不是在这一点上设定的吗？
