我正在尝试添加一个NumberPicker作为对话框，通过按钮按下打开我的活动。现在，当我尝试使用NumberPicker对话框从一个活动移动到活动时，应用程序停止工作。我不明白调试错误试图告诉我什么，有什么帮助吗？
NumberPicker对话框之前的页面
public class RoomDescription extends ActionBarActivity {
public AlertDialog.Builder dialogBuilder;
public List<String> myFixtures = new ArrayList<String>();
public String listItem;
private void setFixtureName()
{
dialogBuilder = new AlertDialog.Builder(this);
final EditText txtInput = new EditText(this);
dialogBuilder.setTitle("New Fixture");
dialogBuilder.setMessage("What is the fixture name?");
dialogBuilder.setView(txtInput);
dialogBuilder.setPositiveButton("Add", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
myFixtures.add(txtInput.getText().toString());
populateListView();
Toast.makeText(getApplicationContext(), "Fixture has been added.", Toast.LENGTH_SHORT).show();
}
});
dialogBuilder.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which)
{
}
});
AlertDialog dialogFixtureName = dialogBuilder.create();
dialogFixtureName.show();
}
private void removeFixture()
{
dialogBuilder = new AlertDialog.Builder(this);
final EditText txtInput = new EditText(this);
dialogBuilder.setTitle("Select Fixture to Remove");
dialogBuilder.setSingleChoiceItems(myFixtures.toArray(new String[myFixtures.size()]), -1, new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
myFixtures.remove(which);
populateListView();
Toast.makeText(getApplicationContext(), "Fixture has been removed.", Toast.LENGTH_SHORT).show();
dialog.dismiss();
}
});
AlertDialog dialogFixtureName = dialogBuilder.create();
dialogFixtureName.show();
}
private void populateListView()
{
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.items, myFixtures);
ListView list = (ListView) findViewById(R.id.FixtureList);
list.setAdapter(adapter);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_room_description);
populateListView();
ListView list = (ListView) findViewById(R.id.FixtureList);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
switch (position) {
default:
Intent i = new Intent(RoomDescription.this, FixtureDescription.class);
TextView textItem = (TextView) view;
String textString = textItem.getText().toString();
i.putExtra("textString",textString);
startActivity(i);
break;
}
}
});
}
@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_room_description, 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;
}
switch (item.getItemId())
{
case R.id.action_settings:
return true;
case R.id.newFixture:
setFixtureName();
break;
case R.id.removeFixture:
removeFixture();
}
return super.onOptionsItemSelected(item);
}
}
NumberPicker对话框页面
public class FixtureDescription extends ActionBarActivity {
public AlertDialog.Builder dialogBuilder;
public int btnFixtureString = 0;
public Button btnFixture = (Button) findViewById(R.id.stepper);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(activity_fixture_description);
TextView textFixture = (TextView) findViewById(R.id.FixtureDescName);
Bundle extras = getIntent().getExtras();
if (extras != null) {
String s = extras.getString("textString");
textFixture.setText(s);
}
btnFixture.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
stepperDialog();
}
});
}
private void stepperDialog() {
final NumberPicker numberPicker;
Button btnAdd;
Button btnCancel;
final Dialog customDialog = new Dialog(this);
customDialog.setContentView(R.layout.numberpicker);
customDialog.setTitle("Number of Fixtures");
numberPicker = (NumberPicker) customDialog.findViewById(R.id.numberPicker);
btnAdd = (Button) customDialog.findViewById(R.id.buttonAdd);
btnCancel = (Button) customDialog.findViewById(R.id.buttonCancel);
numberPicker.setMaxValue(100);
numberPicker.setMinValue(0);
btnAdd.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
btnFixtureString = numberPicker.getValue();
Display();
customDialog.dismiss();
}
});
btnCancel.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
customDialog.dismiss();
}
});
customDialog.show();
}
public void Display()
{
btnFixture.setText(btnFixtureString);
}
@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_fixture_description, 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);
}
}
调试错误报告
07-15 13:59:27.065 11951-11951/com.customledsupply.ledaudit E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.customledsupply.ledaudit, PID: 11951
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.customledsupply.ledaudit/com.customledsupply.ledaudit.FixtureDescription}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2236)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2072)
at com.customledsupply.ledaudit.FixtureDescription.<init>(FixtureDescription.java:21)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1606)
at android.app.Instrumentation.newActivity(Instrumentation.java:1066)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2226)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
答案 0 :(得分：4)
不要像这样初始化这个变量：
public Button btnFixture = (Button) findViewById(R.id.stepper);
您应该在btnFixture内通过findViewById初始化onCreate。