我正在构建一个包含3个文本字段，2个按钮和1个微调框下拉框的警告对话框。其布局在“custom_dialog.xml”中。
然而，当它弹出时，所有项目都为空。我得到一个空指针异常。如果我添加if条件，如下所示，则显示警告对话框，如果没有，我在微调器和按钮上得到空指针异常。
这是代码;请注意，在MainActivity中长按当前视图时会显示警报。
View promptsView = li.inflate(R.layout.custom_dialog, null);
AlertDialog.Builder alert = new AlertDialog.Builder(MainActivity.this);
alert.setView(promptsView);
alert.setIcon(R.drawable.airside);
alert.setTitle("Calculate Distance To");
final TextView from = new TextView(MainActivity.this);
from.setText("From: "+item.getTitle1());
final TextView to1 = new TextView(MainActivity.this);
to1.setText("To: "+item.getTitle1());
final TextView result = (TextView) dialog.findViewById(R.id.txt3);
final AlertDialog alertDialog = alert.create();
final Button btn1 = (Button) dialog.findViewById(R.id.btn1);
final Button btn2 = (Button) dialog.findViewById(R.id.btn2);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_spinner_item,airNames);
Spinner spinner = (Spinner) findViewById(R.id.spinner1);
if (spinner!=null){
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
spinner.setOnItemSelectedListener( new OnItemSelectedListener(){
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
toLat=items.get(position).getPosition().latitude;
toLon=items.get(position).getPosition().longitude;
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
});
}
if (btn1!=null)
btn1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Double dist=calculateDistance(fromLon,fromLat,toLon,toLat);
result.setText(dist.toString());
}
});
if (btn2!=null)
btn2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
dialog.dismiss();
}
});
alert.show();
请检查我是如何使用微调器，btn1和btn2添加if条件的。这意味着每次运行它们都是null。使用if条件，弹出警告对话框，我会看到所有警报框。
EDIT1：
Logcat错误（上面删除了if命令）;
12-02 14:44:17.305: E/OK(7093): LONGCLICKED
12-02 14:44:17.335: E/AndroidRuntime(7093): FATAL EXCEPTION: main
12-02 14:44:17.335: E/AndroidRuntime(7093): Process: com.mapsupport, PID: 7093
12-02 14:44:17.335: E/AndroidRuntime(7093): java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.mapsupport.MainActivity$2.onMapLongClick(MainActivity.java:457)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.android.gms.maps.GoogleMap$9.onMapLongClick(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.android.gms.maps.internal.zzk$zza.onTransact(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at android.os.Binder.transact(Binder.java:380)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.android.gms.maps.internal.bb.a(SourceFile:93)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.gmm6.c.ac.a(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.gmm6.m.bt.f(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.gmm6.m.ak.onLongPress(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.d.g.onLongPress(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.d.h.c(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.google.maps.api.android.lib6.d.i.handleMessage(Unknown Source)
12-02 14:44:17.335: E/AndroidRuntime(7093): at android.os.Handler.dispatchMessage(Handler.java:102)
12-02 14:44:17.335: E/AndroidRuntime(7093): at android.os.Looper.loop(Looper.java:135)
12-02 14:44:17.335: E/AndroidRuntime(7093): at android.app.ActivityThread.main(ActivityThread.java:5375)
12-02 14:44:17.335: E/AndroidRuntime(7093): at java.lang.reflect.Method.invoke(Native Method)
12-02 14:44:17.335: E/AndroidRuntime(7093): at java.lang.reflect.Method.invoke(Method.java:372)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:911)
12-02 14:44:17.335: E/AndroidRuntime(7093): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
答案 0 :(得分：2)
NPE发生，因为微调器位于对话框的布局中，而不在活动的布局中。
添加：
alertDialog.show();
这段代码之后：
final AlertDialog alertDialog = alert.create();
然后在您的alertDialog上调用show（）方法之后>初始化所有视图 之前
TextView result = (TextView) promptsView.findViewById(R.id.txt3);
Spinner spinner = (Spinner) promptsView.findViewById(R.id.spinner1);
final Button btn1 = (Button) promptsView.findViewById(R.id.btn1);
final Button btn2 = (Button) promptsView.findViewById(R.id.btn2);
还要确保在代码末尾删除此行：
alert.show();