我想问..我有2个表单，说它是form1和form2，我在form1上有listview，我想从form2中设置数据。所以我只是创建一个虚拟项目来试试它，我想知道为什么不会工作..
所以这是我在 form2 上的代码：
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.form2);
ArrayList<MyClass> searchResults = GetSearchResults();
form1.listview.setAdapter(new MyAdapter(this, searchResults));
}
private ArrayList<MyClass> GetSearchResults(){
ArrayList<MyClass> results = new ArrayList<MyClass>();
MyClass sr = new MyClass();
sr.setJumlah_menu("Justin Schultz");
sr.setNama_menu("San Francisco, CA");
results.add(sr);
return results;
}
这是我的适配器代码：
public class AdapterListPemesananMenu extends BaseAdapter {
private static ArrayList<MenuInputClass> searchArrayList;
private LayoutInflater mInflater;
public AdapterListPemesananMenu(Context context, ArrayList<MenuInputClass> results) {
searchArrayList = results;
mInflater = LayoutInflater.from(context);
}
public AdapterListPemesananMenu(OnClickListener onClickListener,
ArrayList<MenuInputClass> searchResults) {
// TODO Auto-generated constructor stub
}
public int getCount() {
return searchArrayList.size();
}
public Object getItem(int position) {
return searchArrayList.get(position);
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_pemesananmenu_row, null);
holder = new ViewHolder();
holder.txtName = (TextView) convertView.findViewById(R.id.txtNamaMasuk);
holder.txtCityState = (TextView) convertView
.findViewById(R.id.txtJumlahMasuk);
//holder.txtPhone = (TextView) convertView.findViewById(R.id.phone);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.txtName.setText(searchArrayList.get(position).getNama_menu());
holder.txtCityState.setText(searchArrayList.get(position)
.getJumlah_menu());
return convertView;
}
static class ViewHolder {
TextView txtName;
TextView txtCityState;
}
}
当我从form1转到form2时，它总是强制关闭..
我的代码有什么问题？
当我在form1上尝试代码（来自form2）时，它的工作很好......
这是来自logcat：
10-22 04:33:30.647: E/AndroidRuntime(15247): FATAL EXCEPTION: main
10-22 04:33:30.647: E/AndroidRuntime(15247): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aplikasipemesananmenu/list_pemesananmenu_view.SingleListView_Activity}: java.lang.NullPointerException
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.os.Handler.dispatchMessage(Handler.java:99)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.os.Looper.loop(Looper.java:130)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread.main(ActivityThread.java:3693)
10-22 04:33:30.647: E/AndroidRuntime(15247): at java.lang.reflect.Method.invokeNative(Native Method)
10-22 04:33:30.647: E/AndroidRuntime(15247): at java.lang.reflect.Method.invoke(Method.java:507)
10-22 04:33:30.647: E/AndroidRuntime(15247): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
10-22 04:33:30.647: E/AndroidRuntime(15247): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
10-22 04:33:30.647: E/AndroidRuntime(15247): at dalvik.system.NativeStart.main(Native Method)
10-22 04:33:30.647: E/AndroidRuntime(15247): Caused by: java.lang.NullPointerException
10-22 04:33:30.647: E/AndroidRuntime(15247): at list_pemesananmenu_view.SingleListView_Activity.onCreate(SingleListView_Activity.java:67)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-22 04:33:30.647: E/AndroidRuntime(15247): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
10-22 04:33:30.647: E/AndroidRuntime(15247): ... 11 more
10-22 04:33:31.958: E/DataRouter(125): smd_file_fd = 16 and external_file_fd = 24
10-22 04:33:31.958: E/DataRouter(125): ==KDW(3)== smd_new_status = (358)
10-22 04:33:31.958: E/DataRouter(125): ==KDW(4)== smd_new_status = (320)
10-22 04:33:31.958: E/DataRouter(125): DCD pinstatus is ON
任何帮助都会感谢谢谢...
答案 0 :(得分：0)
如何在form2.onCreate（）方法上设置form1？ 好像NPE在form1.listview.setAdapter上（new MyAdapter（this，searchResults））;等。
我认为你不应该在另一个中使用一个活动对象，因为系统可以随时杀死使用过的对象。在http://developer.android.com/reference/android/app/Activity.html和http://developer.android.com/training/basics/activity-lifecycle/index.html处查看活动生命周期。
使用自定义Application类在活动和Activity.onResume（）方法之间传递数据，以使用名为Activity的listview上的新数据。
如果您不知道如何制作它，请询问相同的示例代码。
Eddited（下面的代码）
创建自定义应用程序对象：
public class MyApplication extends Application {
Object mData;
public Object getData() {
return mData;
}
public void setData(Object data) {
mData = data;
}
}
在清单中使用它：
<application
android:name="my.apppkg.MyApplication"
...
</application>
并创建两个活动。 Form1作为“消费者”：
public class Form1 extends Activity {
MyApplication mApp;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mApp = (MyApplication)getApplication();
}
@Override
protected void onResume() {
super.onResume();
Object data = mApp.getData();
if (data != null) {
// Do whatever you want with the data
} else {
// No data
}
}
...
}
和Form2作为“生产者”：
public class Form2 extends Activity {
MyApplication mApp;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mApp = (MyApplication)getApplication();
}
...
/**
* Data generation method. Calls to Form1 once the data is set.
* Call it here or from wherever you need it to (Buttons onClick events, ListViews onItemListClick, etc)
*/
private void processAndSendData() {
Object newData = ...; // Get the data from your sources
mApp.setData(newData);
Intent intent = new Intent(this, Form1.class);
this.startActivity(intent);
}
}
当然，根据需要更改MyApplication类（示例中的Object）中的mData类型。