这里我有一个mechanic.java文件，它接受一个特定的textview值并传递给FetchData.java文件，在该文件中已完成数据库操作以从数据库中检索数据，并应显示在ListView中。
public class MechanicPage extends Activity {
public ListView list;
EditText cityName;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mechanic_page);
cityName = (EditText) findViewById(R.id.place);
Resources res = getResources();
}
public void onclick(View view) {
FetchData fetchData = new FetchData(this);
String city = cityName.getText().toString();
Profile p = fetchData.getData(city);
list = (ListView) findViewById(android.R.id.list);
ListAdapter adopt = new ListAdapter(this, p);
list.setAdapter(adopt);
}
}
class ListAdapter extends ArrayAdapter < Profile > {
Context context;
Profile profile;
public EditText etName,
etContact;
public ListAdapter(Context context, Profile objects) {
super(context, R.layout.data_list);
try {
this.context = context;
this.profile = objects;
} catch (SQLException e) {
Message.message(context, "" + e);
}
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View row = convertView;
if (row == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
//row object has refrence to the relative layout of single_row layout file
row = inflater.inflate(R.layout.data_list, parent, false);
}
etName = (EditText) row.findViewById(R.id.name);
etContact = (EditText) row.findViewById(R.id.contact);
String name = profile.getName();
int contact = profile.getContact();
etName.setText(name);
etContact.setText(contact);
return row;
}
}
这是FetchData.java文件，它执行数据库操作以检索数据并返回对象。
import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;
/**
* Created by lathass on 24/04/17.
*/
public class FetchData {
DatabaseOpenHelper openHelper;
SQLiteDatabase database;
Context context;
String name;
int contact;
ListView list;
Profile profile = new Profile(name, contact);
public FetchData(Context context) {
openHelper = new DatabaseOpenHelper(context);
}
public Profile getData(String city) {
database = openHelper.getWritableDatabase();
String[] col = {
DatabaseOpenHelper.NAME,
DatabaseOpenHelper.PHONE
};
Cursor c = null;
try {
c = database.query(DatabaseOpenHelper.TABLE1, col, DatabaseOpenHelper.CITY + " = ?", new String[] {
city
}, null, null, null);
c.moveToFirst();
while (!c.isAfterLast()) {
name = c.getString(c.getColumnIndex(DatabaseOpenHelper.NAME));
profile.setName(name);
contact = c.getInt(c.getColumnIndex(DatabaseOpenHelper.PHONE));
profile.setContact(contact);
c.moveToNext();
}
c.close();
} catch (SQLException e) {
Message.message(context, "" + e);
}
return profile;
}
public class DatabaseOpenHelper extends SQLiteAssetHelper {
private static final String DB_NAME = "Data.db";
private static final int DB_VERSION = 1;
private static final String TABLE1 = "mechanic";
private static final String TABLE2 = "lodge";
private static final String TABLE3 = "travels";
private static final String NAME = "Name";
private static final String PHONE = "Phone";
private static final String CITY = "City";
Context context;
public DatabaseOpenHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.context = context;
}
}
public void close() {
if (database != null)
this.database.close();
}
}
这是LogCat
05 - 04 00: 45: 53.402 2777 - 6542 / com.google.android.gms.unstable W / DG.WV: Widevine DRM not supported on this device
android.media.UnsupportedSchemeException: Failed to instantiate drm object.
at android.media.MediaDrm.native_setup(Native Method)
at android.media.MediaDrm. < init > (MediaDrm.java: 180)
at ono.a(: com.google.android.gms: 122)
at okh.run(: com.google.android.gms: 1095)
at lmq.run(: com.google.android.gms: 450)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java: 1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java: 587)
at lra.run(: com.google.android.gms: 17)
at java.lang.Thread.run(Thread.java: 818)
05 - 04 00: 45: 53.409 1948 - 6539 / com.google.android.gms.persistent I / GoogleURLConnFactory: Using platform SSLCertificateSocketFactory
05 - 04 00: 45: 53.496 1730 - 1846 / system_process W / AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client
05 - 04 00: 45: 53.499 6028 - 6028 / com.project.mechfinder I / SQLiteAssetHelper: successfully opened database Data.db
05 - 04 00: 45: 53.535 1730 - 2010 / system_process I / art: Explicit concurrent mark sweep GC freed 41029(2 MB) AllocSpace objects, 20(377 KB) LOS objects, 30 % free, 8 MB / 12 MB, paused 1.254 ms total 33.640 ms
05 - 04 00: 45: 54.149 1948 - 6539 / com.google.android.gms.persistent I / GoogleURLConnFactory: Using platform SSLCertificateSocketFactory
[05 - 04 00: 45: 54.279 2777: 2792 D / ]
HostConnection::get() New Host Connection established 0xb429f7c0, tid 2792
05 - 04 00: 45: 54.678 1948 - 6539 / com.google.android.gms.persistent W / Uploader: no longer exists, so no auth token.
05 - 04 00: 45: 54.819 1948 - 2471 / com.google.android.gms.persistent W / Conscrypt: Could not set socket write timeout: null
05 - 04 00: 45: 54.988 1948 - 2471 / com.google.android.gms.persistent W / Conscrypt: Could not set socket write timeout: null
05 - 04 00: 45: 55.648 1948 - 2471 / com.google.android.gms.persistent W / GLSUser: [AppCertManager] IOException
while requesting key:
java.io.IOException: Invalid device key response.
at ewg.a(: com.google.android.gms: 274)
at ewg.a(: com.google.android.gms: 4238)
at ewf.a(: com.google.android.gms: 45)
at evz.a(: com.google.android.gms: 50)
at evy.a(: com.google.android.gms: 104)
at com.google.android.gms.auth.account.be.legacy.AuthCronChimeraService.b(: com.google.android.gms: 4049)
at edi.call(: com.google.android.gms: 2041)
at java.util.concurrent.FutureTask.run(FutureTask.java: 237)
at lmq.run(: com.google.android.gms: 450)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java: 1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java: 587)
at lra.run(: com.google.android.gms: 17)
at java.lang.Thread.run(Thread.java: 818)
05 - 04 00: 46: 43.520 6028 - 6028 / com.project.mechfinder I / SQLiteAssetHelper: successfully opened database Data.db
05 - 04 00: 46: 43.521 1730 - 1846 / system_process W / AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client
05 - 04 00: 46: 53.720 1730 - 1846 / system_process W / AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client
05 - 04 00: 46: 53.724 6028 - 6028 / com.project.mechfinder I / SQLiteAssetHelper: successfully opened database Data.db
05 - 04 00: 47: 00.822 1730 - 1846 / system_process W / AudioTrack: AUDIO_OUTPUT_FLAG_FAST denied by client
05 - 04 00: 47: 00.825 6028 - 6028 / com.project.mechfinder I / SQLiteAssetHelper: successfully opened database Data.db
答案 0 :(得分：0)
我在这里疯狂猜测，因为没有Logcat。
如果您要设置自己的布局（而不是从ListActivity扩展），则很可能您没有使用android.R.id.list作为View ID。
因此，您使用此ID检索ListView引用这一事实让我觉得它在NullPointerException list.setAdapter(adopt);上爆炸了。
编辑：
您必须在xml中为ListView定义自己的ID，而不是调用findViewById(android.R.id.list);，而应使用findViewById(R.id.your_list_id);