我的MainActivity打开时所有小部件都正常工作，但当我选择按钮打开我的第二个活动时，它无法打开并且应用程序崩溃。 Eclipse没有显示错误
我的主要活动课程：
public class MainActivity extends FragmentActivity {
private int dYear;
private int dMonth;
private int dDay;
private int rYear;
private int rMonth;
private int rDay;
static final int dDATE_DIALOG_ID = 0;
static final int rDATE_DIALOG_ID = 1;
private RadioButton buttonO = null;
private RadioButton buttonR = null;
private TableRow tr;
TextView txD, txR;
private Button btnDepart,btnReturn, btnSubmit,btnClose;
private Spinner noOfPassengersSpinner,departureSpinner,returnSpinner;
private CheckBox tandCCB;
final Context context = this;
private Bundle basket;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonO = (RadioButton) findViewById(R.id.radioO);
buttonR = (RadioButton) findViewById(R.id.radioR);
txD=(TextView)findViewById(R.id.tvDepartureDate);
txR=(TextView)findViewById(R.id.tvReturnDate);
btnDepart = (Button)findViewById(R.id.btnDepart);
btnReturn = (Button)findViewById(R.id.btnReturn);
tr = (TableRow)findViewById(R.id.tableRow5);
btnSubmit = (Button)findViewById(R.id.btnSubmit);
btnClose = (Button)findViewById(R.id.btnClose);
noOfPassengersSpinner = (Spinner)findViewById(R.id.noOfPassengersSpinner);
departureSpinner = (Spinner)findViewById(R.id.departureSpinner);
returnSpinner = (Spinner)findViewById(R.id.returnSpinner);
tandCCB = (CheckBox)findViewById(R.id.tandCCB);
final Calendar dC = Calendar.getInstance();
final Calendar rC = Calendar.getInstance();
dYear = dC.get(Calendar.YEAR);
dMonth = dC.get(Calendar.MONTH);
dDay = dC.get(Calendar.DAY_OF_MONTH);
rYear = rC.get(Calendar.YEAR);
rMonth = rC.get(Calendar.MONTH);
rDay = rC.get(Calendar.DAY_OF_MONTH);
updateDisplay();
tandCCB.setOnCheckedChangeListener(new OnCheckedChangeListener()
{
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked)
{
if(isChecked){
btnSubmit.setEnabled(true);
}
else{
btnSubmit.setEnabled(false);
}
}
});
this.btnClose.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
finish();
System.exit(0);
}
});
this.btnSubmit.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
String depAir = departureSpinner.getSelectedItem().toString();
String desAir = returnSpinner.getSelectedItem().toString();
int numOfPass = Integer.parseInt(noOfPassengersSpinner.getSelectedItem().toString());
basket.putString("departureAir", depAir);
basket.putString("destenationAir", desAir);
basket.putInt("numOfPass", numOfPass);
basket.putString("depDate", txD.getText().toString());
String type = "";
if(buttonR.isChecked()){
String returnDate = txR.getText().toString();
basket.putString("returnDate", returnDate);
type = "Return";
}
else{
type = "Oneway";
}
basket.putString("type", type);
Intent intent = new Intent(context, Second.class);
intent.putExtras(basket);
startActivity(intent);
}
});
this.buttonO.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
tr.setVisibility(View.GONE);
}
});
this.buttonR.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
tr.setVisibility(View.VISIBLE);
}
});
this.btnDepart.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
showDialog(dDATE_DIALOG_ID);
}
});
this.btnReturn.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
showDialog(rDATE_DIALOG_ID);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
private void updateDisplay() {
txD.setText(
new StringBuilder()
// Month is 0 based so add 1
.append(dYear).append("-")
.append(dMonth + 1).append("-")
.append(dDay).append(" ")
);
txR.setText(
new StringBuilder()
.append(rYear).append("-")
.append(rMonth + 1).append("-")
.append(rDay).append(" ")
);
}
private DatePickerDialog.OnDateSetListener dDateSetListener =
new DatePickerDialog.OnDateSetListener() {
public void onDateSet(DatePicker view, int year,
int monthOfYear, int dayOfMonth) {
dYear = year;
dMonth = monthOfYear;
dDay = dayOfMonth;
updateDisplay();
}
};
private DatePickerDialog.OnDateSetListener rDateSetListener =
new DatePickerDialog.OnDateSetListener() {
public void onDateSet(DatePicker view, int year,
int monthOfYear, int dayOfMonth) {
rYear = year;
rMonth = monthOfYear;
rDay = dayOfMonth;
updateDisplay();
}
};
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case dDATE_DIALOG_ID:
return new DatePickerDialog(this,
dDateSetListener,
dYear, dMonth, dDay);
case rDATE_DIALOG_ID:
return new DatePickerDialog(this,
rDateSetListener,
rYear, dMonth, rDay);
}
return null;
}
}
我的第二项活动是：
public class Second extends Activity {
private TextView typeTv, departureTv,returnTv,departureDateTv,returnDateTv,noOfPassengersTv,tvReturnDateLbl;
private RadioButton buttonR = null;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second);
typeTv = (TextView)findViewById(R.id.typeTv);
departureTv = (TextView)findViewById(R.id.departureTv);
returnTv = (TextView)findViewById(R.id.returnTv);
departureDateTv= (TextView)findViewById(R.id.departureTv);
returnDateTv= (TextView)findViewById(R.id.returneDateTv);
noOfPassengersTv = (TextView)findViewById(R.id.noOfPassengersTv);
buttonR = (RadioButton) findViewById(R.id.radioR);
tvReturnDateLbl = (TextView)findViewById(R.id.tvReturnDateLbl);
Intent i = getIntent();//MAking an intent called i
Bundle basket = this.getIntent().getExtras();
String tTv = basket.getString("type");
String dTv = basket.getString("departureAir");
String rTv = basket.getString("destinationAir");
String dDTv = basket.getString("depDateTv");
int nOPTv = basket.getInt("numOfPass");
if(buttonR.isChecked()){
String rDTv = basket.getString("returnDate");
returnDateTv.setText(rDTv);
}
else{
returnDateTv.setVisibility(View.GONE);
tvReturnDateLbl.setVisibility(View.GONE);
}
typeTv.setText(tTv);
departureTv.setText(dTv);
returnTv.setText(rTv);
departureDateTv.setText(dDTv);
noOfPassengersTv.setText(""+nOPTv);
}
}
最后我的清单文件是：
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="15" />
<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Second"
android:label="@string/app_name">
</activity>
</application>
我的LogCat
04-25 19:04:11.912: E/AndroidRuntime(999): FATAL EXCEPTION: main
04-25 19:04:11.912: E/AndroidRuntime(999): java.lang.NullPointerException
04-25 19:04:11.912: E/AndroidRuntime(999): at com.example.assignment2.MainActivity$5.onClick(MainActivity.java:121)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.view.View.performClick(View.java:4084)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.view.View$PerformClick.run(View.java:16966)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.os.Handler.handleCallback(Handler.java:615)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.os.Handler.dispatchMessage(Handler.java:92)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.os.Looper.loop(Looper.java:137)
04-25 19:04:11.912: E/AndroidRuntime(999): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-25 19:04:11.912: E/AndroidRuntime(999): at java.lang.reflect.Method.invokeNative(Native Method)
04-25 19:04:11.912: E/AndroidRuntime(999): at java.lang.reflect.Method.invoke(Method.java:511)
04-25 19:04:11.912: E/AndroidRuntime(999): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-25 19:04:11.912: E/AndroidRuntime(999): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-25 19:04:11.912: E/AndroidRuntime(999): at dalvik.system.NativeStart.main(Native Method)
我的新logcat
04-25 19:38:14.443: E/Trace(1155): error opening trace file: No such file or directory (2)
04-25 19:38:15.282: D/gralloc_goldfish(1155): Emulator without GPU emulation detected.
04-25 19:38:19.251: D/AndroidRuntime(1155): Shutting down VM
04-25 19:38:19.251: W/dalvikvm(1155): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
04-25 19:38:19.281: E/AndroidRuntime(1155): FATAL EXCEPTION: main
04-25 19:38:19.281: E/AndroidRuntime(1155): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.assignment2/com.example.assignment2.Second}: java.lang.NullPointerException
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread.access$600(ActivityThread.java:130)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.os.Handler.dispatchMessage(Handler.java:99)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.os.Looper.loop(Looper.java:137)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread.main(ActivityThread.java:4745)
04-25 19:38:19.281: E/AndroidRuntime(1155): at java.lang.reflect.Method.invokeNative(Native Method)
04-25 19:38:19.281: E/AndroidRuntime(1155): at java.lang.reflect.Method.invoke(Method.java:511)
04-25 19:38:19.281: E/AndroidRuntime(1155): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-25 19:38:19.281: E/AndroidRuntime(1155): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-25 19:38:19.281: E/AndroidRuntime(1155): at dalvik.system.NativeStart.main(Native Method)
04-25 19:38:19.281: E/AndroidRuntime(1155): Caused by: java.lang.NullPointerException
04-25 19:38:19.281: E/AndroidRuntime(1155): at com.example.assignment2.Second.onCreate(Second.java:46)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.Activity.performCreate(Activity.java:5008)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
04-25 19:38:19.281: E/AndroidRuntime(1155): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
04-25 19:38:19.281: E/AndroidRuntime(1155): ... 11 more
04-25 19:38:19.441: D/dalvikvm(1155): GC_CONCURRENT freed 163K, 3% free 8303K/8519K, paused 79ms+112ms, total 315ms
答案 0 :(得分：1)
我相信basket是null。您需要先对其进行初始化，然后才能在其上调用put()
Bundle basket = new Bundle();
了解如何阅读logcat对于调试工作势在必行。看看上面的输出
04-25 19:04:11.912: E/AndroidRuntime(999): FATAL EXCEPTION: main
04-25 19:04:11.912: E/AndroidRuntime(999): java.lang.NullPointerException
04-25 19:04:11.912: E/AndroidRuntime(999): at
com.example.assignment2.MainActivity$5.onClick(MainActivity.java:121)
从这里我们可以看到NPE
MainAcitivty
*编辑**
在Second中改变你获得额外内容的方式。变化
Intent i = getIntent();//MAking an intent called i
Bundle basket = this.getIntent().getExtras();
到
Intent i = getIntent();//MAking an intent called i
Bundle basket = i.getBundleExtra("basket");
由于您将Bundle放入Intent而不是每个extra本身，因此您可以这样做。如果您已将每个extra放入其中，那么您将获得Bundle当前拥有它的方式。
See this so answer（第二个）它可能会更清楚。
在您的第一次Activity更改
intent.putExtras(basket);
到
intent.putExtra("basket", basket);