我正在进行一个测验，其中需要将问题和答案列表从活动1传递到活动2.相关的编码提取如下：
String[] NUM_ALLL_QuestionNames;
String[] NUM_ALLL_AnswerNames;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main_num_index);
Button ButtonStart= (Button) findViewById(R.id.buttonStart);
ButtonStart.setOnClickListener(startButtonListener);
Button ButtonBackkk= (Button) findViewById(R.id.buttonBackkk);
CheckTextView = (TextView) findViewById(R.id.checktextView);
NUM_SIM_QuestionNames = getResources().getStringArray(R.array.Num_Q_Simple_List);
NUM_MED_QuestionNames = getResources().getStringArray(R.array.Num_Q_Medium_List);
NUM_DIF_QuestionNames = getResources().getStringArray(R.array.Num_Q_Diff_List);
NUM_EXP_QuestionNames = getResources().getStringArray(R.array.Num_Q_Expert_List);
NUM_SIM_AnswerNames = getResources().getStringArray(R.array.Num_A_Simple_List);
NUM_MED_AnswerNames = getResources().getStringArray(R.array.Num_A_Medium_List);
NUM_DIF_AnswerNames = getResources().getStringArray(R.array.Num_A_Diff_List);
NUM_EXP_AnswerNames = getResources().getStringArray(R.array.Num_A_Expert_List);
NUM_ALL_QuestionNames = new ArrayList<String>();
NUM_ALL_AnswerNames = new ArrayList<String>();
};
private OnClickListener startButtonListener = new OnClickListener()
{
@Override
public void onClick(View v)
{
CheckBox CheckSim = (CheckBox) findViewById(R.id.checkBox2);
// other similar checkBox omitted here for simplicity //
NUM_ALL_QuestionNames.clear();
NUM_ALL_AnswerNames.clear();
if (CheckSim.isChecked())
{
QuestionImport= 0;
QuestionImport = NUM_SIM_QuestionNames.length;
int i =0;
while (i<QuestionImport)
{
String Q_toimport = NUM_SIM_QuestionNames[i];
String A_toimport = NUM_SIM_AnswerNames[i];
NUM_ALL_QuestionNames.add(Q_toimport);
NUM_ALL_AnswerNames.add(A_toimport);
++i;
}
};
// other similar checkBox omitted here for simplicity //
if ((!CheckSim.isChecked()) && (!CheckMed.isChecked()) && (!CheckDif.isChecked()) && (!CheckExp.isChecked()))
{
int k = 0;
if (NUM_ALL_QuestionNames.size() >0) {k= NUM_ALL_QuestionNames.size();}
CheckTextView.setText(String.valueOf(k));
AlertDialog.Builder builder = new AlertDialog.Builder(Num_index.this);
builder.setTitle("Error");
builder.setMessage("Please select at least one choice!!");
builder.setCancelable(false);
builder.setPositiveButton("OK", null);
AlertDialog ErrorDialog = builder.create();
ErrorDialog.show();
}
if ((CheckSim.isChecked()) || (CheckMed.isChecked()) || (CheckDif.isChecked()) || (CheckExp.isChecked()))
{
NUM_ALLL_QuestionNames = new String[NUM_ALL_QuestionNames.size()]; //convert ArrayList<String> to String[]
NUM_ALLL_AnswerNames = new String[NUM_ALL_AnswerNames.size()]; //convert ArrayList<String> to String[]
Intent senddata = new Intent (Num_index.this, Num.class); //transmit the list to num.java
Bundle bundle = new Bundle();
bundle.putStringArray("dataQ",NUM_ALLL_QuestionNames);
bundle.putStringArray("dataA",NUM_ALLL_AnswerNames);
senddata.putExtras(bundle);
startActivity(senddata);
int k = 0;
if (NUM_ALLL_QuestionNames.length >0) {k= NUM_ALLL_QuestionNames.length;}
CheckTextView.setText(String.valueOf(k));
}
Intent intent = new Intent (Num_index.this, Num.class);
startActivity(intent);
Num_index.this.finish();
} // end method onClick
}; // end OnClickListener
private String[] NUM_ALL_QuestionNames;
private String[] NUM_ALL_AnswerNames;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main_num);
//get bundle from Num_index.java
Bundle bundle = this.getIntent().getExtras();
if (bundle!= null)
{
NUM_ALL_QuestionNames = bundle.getStringArray("dataQ");
NUM_ALL_AnswerNames = bundle.getStringArray("dataA");
}
else
{
NUM_ALL_QuestionNames = getResources().getStringArray(R.array.Num_Q_Simple_List);
NUM_ALL_AnswerNames = getResources().getStringArray(R.array.Num_A_Simple_List);
}
11-18 20:26:20.905: E/AndroidRuntime(5463): FATAL EXCEPTION: main
11-18 20:26:20.905: E/AndroidRuntime(5463): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pearappx.iq_3/com.pearappx.iq_3.Num}: java.lang.NullPointerException
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread.access$600(ActivityThread.java:127)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.os.Handler.dispatchMessage(Handler.java:99)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.os.Looper.loop(Looper.java:137)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread.main(ActivityThread.java:4511)
11-18 20:26:20.905: E/AndroidRuntime(5463): at java.lang.reflect.Method.invokeNative(Native Method)
11-18 20:26:20.905: E/AndroidRuntime(5463): at java.lang.reflect.Method.invoke(Method.java:511)
11-18 20:26:20.905: E/AndroidRuntime(5463): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
11-18 20:26:20.905: E/AndroidRuntime(5463): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
11-18 20:26:20.905: E/AndroidRuntime(5463): at dalvik.system.NativeStart.main(Native Method)
11-18 20:26:20.905: E/AndroidRuntime(5463): Caused by: java.lang.NullPointerException
11-18 20:26:20.905: E/AndroidRuntime(5463): at com.pearappx.iq_3.Num.onCreate(Num.java:73)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.Activity.performCreate(Activity.java:4470)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
11-18 20:26:20.905: E/AndroidRuntime(5463): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
第73行
NUM_ALL_QuestionNames = bundle.getStringArray("dataQ");
表示StringArray没有正确存储在Activity1中，或者无法在Activity2中正确获取。它显示NullPointerException。
我搜索过这个网站，如String back from Bundle和How to pass the selectedListItem's object to another activity?，并按照所描述的方法进行搜索，但仍然失败。但为什么它是NullPointerException？怎么解决这个问题？
非常感谢!!
PS：在活动1中我有
if (NUM_ALLL_QuestionNames.length >0) {k= NUM_ALLL_QuestionNames.length;}
CheckTextView.setText(String.valueOf(k));
和k给出正确数量的项目。这意味着NUM_ALLL_QuestionNames不为空。
答案 0 :(得分：4)
http://developer.android.com/guide/components/activities.html#StartingAnActivity
您应该发送第二个意图的数据包。并完全删除第一个意图。
答案 1 :(得分：2)
与您的当前代码一样，您首先使用Num.class开始startActivity(senddata);活动两次，而第二次startActivity(intent);不包含任何捆绑对象，这就是您获得NullPointerException <的原因/ p>