在新 activity 错误 null 异常中打开意图时应用程序崩溃？
app crashes when opening intent in new activity error nullexception?
我对这一切都很陌生，但我对一些我无法弄清楚的事情感到很困惑。我查看了许多以前提出的问题，但无济于事。我正在尝试将一个值从列表视图传递到新的 activity。我正在使用意图，选定的值确实得到了很好的注册（在我的 mainactivity 和日志中用一个简单的文本视图检查了它。但是当我想在我的新 activity 中检索它们时应用程序崩溃。所以我想问题出在我的第二个 activity 中的某个地方。非常感谢帮助。（ps。我的代码可能需要清理，但稍后我会解决这个问题。）
我的 main_activity:
public class MainActivity extends Activity implements View.OnClickListener, AdapterView.OnItemClickListener {
EditText logedit;
EditText logexistedit;
Button logbutton;
Button logexistbutton;
ListView lognaamlist;
ArrayAdapter userArrayAdapter;
ArrayList userList = new ArrayList();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
logedit=(EditText)findViewById(R.id.logedit);
logbutton = (Button) findViewById(R.id.logbutton);
logbutton.setOnClickListener(this);
lognaamlist=(ListView)findViewById(R.id.listView);
logexistbutton = (Button)findViewById(R.id.existlogbutton);
logexistbutton.setOnClickListener(this);
lognaamlist = (ListView) findViewById(R.id.listView);
Firebase.setAndroidContext(this);
userArrayAdapter = new ArrayAdapter<String>(this,
R.layout.activity_loginrow, R.id.loginnaam,
userList);
LoadPreferences();
lognaamlist.setAdapter(userArrayAdapter);
lognaamlist.setOnItemClickListener(this);
}
protected void SavePreferences(String key, String value) {
// TODO Auto-generated method stub
SharedPreferences data = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = data.edit();
editor.putString(key, value);
editor.commit();
}
protected void LoadPreferences(){
SharedPreferences data = PreferenceManager.getDefaultSharedPreferences(this);
String dataSet = data.getString("LISTS", "None Available");
userArrayAdapter.add(dataSet);
userArrayAdapter.notifyDataSetChanged();
}
private void actienaam(String String) {
Firebase ref = new Firebase("https://packagename.firebaseio.com/lijstapp");
String savename = (((logedit.getText().toString())));
Firebase userRef = ref.child("users");
Map<String, Object> rec1 = new HashMap<String, Object>();
rec1.put(savename, savename);
userRef.updateChildren(rec1);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.logbutton:
actienaam(((logedit.getText().toString())));
// Also add that value to the list shown in the ListView
userList.add(logedit.getText().toString());
userArrayAdapter.notifyDataSetChanged();
SavePreferences("LISTS", (logedit.getText().toString()));
break;
case R.id.existlogbutton:
userList.add(logedit.getText().toString());
userArrayAdapter.notifyDataSetChanged();
SavePreferences("LISTS", (logedit.getText().toString()));
break;
default:
break;
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String userdata = (String) userList.get(position);
Intent i = new Intent(MainActivity.this, Keuzelijstactivity.class);
i.putExtra("userdata", userdata);
startActivity(i);
// Log the item's position and contents
// to the console in Debug
//later veranderen in volgende stap
Log.d("omg android", position + ": " + userList.get(position));
}}
我的第二个activity:
public class Keuzelijstactivity extends Activity {
TextView boodschaptext;
TextView takentext;
TextView test;
String userdata;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);
setContentView(R.layout.lijsten_layout);
Firebase.setAndroidContext(this);
Intent i = getIntent();
userdata= i.getStringExtra("userdata");
test.setText(userdata);
}
最后我的 logcat 崩溃时：
01-26 22:21:13.205 834-834/prolijst.rob.com.prolijst E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{prolijst.rob.com.prolijst/prolijst.rob.com.prolijst.Keuzelijstactivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access0(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at prolijst.rob.com.prolijst.Keuzelijstactivity.onCreate(Keuzelijstactivity.java:30)
at android.app.Activity.performCreate(Activity.java:5008)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access0(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
问题就在这里
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);
setContentView(R.layout.lijsten_layout);
您在调用 setContentView(R.layout.lijsten_layout); 之前已经初始化了您的视图，这就是您收到 NPE 异常的原因。所以只需将其更改为
setContentView(R.layout.lijsten_layout);
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);
我对这一切都很陌生，但我对一些我无法弄清楚的事情感到很困惑。我查看了许多以前提出的问题，但无济于事。我正在尝试将一个值从列表视图传递到新的 activity。我正在使用意图，选定的值确实得到了很好的注册（在我的 mainactivity 和日志中用一个简单的文本视图检查了它。但是当我想在我的新 activity 中检索它们时应用程序崩溃。所以我想问题出在我的第二个 activity 中的某个地方。非常感谢帮助。（ps。我的代码可能需要清理，但稍后我会解决这个问题。） 我的 main_activity:
public class MainActivity extends Activity implements View.OnClickListener, AdapterView.OnItemClickListener {
EditText logedit;
EditText logexistedit;
Button logbutton;
Button logexistbutton;
ListView lognaamlist;
ArrayAdapter userArrayAdapter;
ArrayList userList = new ArrayList();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
logedit=(EditText)findViewById(R.id.logedit);
logbutton = (Button) findViewById(R.id.logbutton);
logbutton.setOnClickListener(this);
lognaamlist=(ListView)findViewById(R.id.listView);
logexistbutton = (Button)findViewById(R.id.existlogbutton);
logexistbutton.setOnClickListener(this);
lognaamlist = (ListView) findViewById(R.id.listView);
Firebase.setAndroidContext(this);
userArrayAdapter = new ArrayAdapter<String>(this,
R.layout.activity_loginrow, R.id.loginnaam,
userList);
LoadPreferences();
lognaamlist.setAdapter(userArrayAdapter);
lognaamlist.setOnItemClickListener(this);
}
protected void SavePreferences(String key, String value) {
// TODO Auto-generated method stub
SharedPreferences data = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = data.edit();
editor.putString(key, value);
editor.commit();
}
protected void LoadPreferences(){
SharedPreferences data = PreferenceManager.getDefaultSharedPreferences(this);
String dataSet = data.getString("LISTS", "None Available");
userArrayAdapter.add(dataSet);
userArrayAdapter.notifyDataSetChanged();
}
private void actienaam(String String) {
Firebase ref = new Firebase("https://packagename.firebaseio.com/lijstapp");
String savename = (((logedit.getText().toString())));
Firebase userRef = ref.child("users");
Map<String, Object> rec1 = new HashMap<String, Object>();
rec1.put(savename, savename);
userRef.updateChildren(rec1);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.logbutton:
actienaam(((logedit.getText().toString())));
// Also add that value to the list shown in the ListView
userList.add(logedit.getText().toString());
userArrayAdapter.notifyDataSetChanged();
SavePreferences("LISTS", (logedit.getText().toString()));
break;
case R.id.existlogbutton:
userList.add(logedit.getText().toString());
userArrayAdapter.notifyDataSetChanged();
SavePreferences("LISTS", (logedit.getText().toString()));
break;
default:
break;
}
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String userdata = (String) userList.get(position);
Intent i = new Intent(MainActivity.this, Keuzelijstactivity.class);
i.putExtra("userdata", userdata);
startActivity(i);
// Log the item's position and contents
// to the console in Debug
//later veranderen in volgende stap
Log.d("omg android", position + ": " + userList.get(position));
}}
我的第二个activity:
public class Keuzelijstactivity extends Activity {
TextView boodschaptext;
TextView takentext;
TextView test;
String userdata;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);
setContentView(R.layout.lijsten_layout);
Firebase.setAndroidContext(this);
Intent i = getIntent();
userdata= i.getStringExtra("userdata");
test.setText(userdata);
}
最后我的 logcat 崩溃时：
01-26 22:21:13.205 834-834/prolijst.rob.com.prolijst E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{prolijst.rob.com.prolijst/prolijst.rob.com.prolijst.Keuzelijstactivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access0(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at prolijst.rob.com.prolijst.Keuzelijstactivity.onCreate(Keuzelijstactivity.java:30)
at android.app.Activity.performCreate(Activity.java:5008)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access0(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
问题就在这里
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);
setContentView(R.layout.lijsten_layout);
您在调用 setContentView(R.layout.lijsten_layout); 之前已经初始化了您的视图，这就是您收到 NPE 异常的原因。所以只需将其更改为
setContentView(R.layout.lijsten_layout);
boodschaptext = (TextView) findViewById(R.id.boodschappenlijst);
takentext = (TextView) findViewById(R.id.takenlijst);
test = (TextView)findViewById(R.id.test);