当我试图在列表活动中显示对话框时出现NullPointerException

Question

我试图在用户单击某个项目时创建一个活动，它显示对话框。当我尝试在列表活动中显示对话框时出现错误。它立即崩溃，并出现NullPointerException异常。

public void onCreate(Bundle icicle) { 
    super.onCreate(icicle); 
    String[] values = new String[] { 
      "Créer un Point", 
      "Relever Ma position actuelle", 
      "Importer Geotiff", 
      "Importer KML", 
      "Exporter" }; 
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, 
     R.layout.menu_activity, R.id.label, values); 
    setListAdapter(adapter); 
    } 

    @Override 
    protected void onListItemClick(ListView l, View v, int position, long id) { 
    String item = (String) getListAdapter().getItem(position); 
        if(item.equals("Importer Geotiff")||item.equals("Importer KML")){ 
         { 
         Intent intent = new Intent(this,FileChooser.class); 
           startActivity(intent); 
         }} 
        else if(item.equals("Exporter")) 
        { 
         final Dialog dialog = new Dialog(this); 
         dialog.setContentView(R.layout.dialog_nom_fichier); 
         dialog.setTitle("Nom"); 
         dialog.show(); 
         } 
Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show(); 

         } 

，误差

03-30 00:56:01.465: E/AndroidRuntime(30155): FATAL EXCEPTION: main 
03-30 00:56:01.465: E/AndroidRuntime(30155): java.lang.NullPointerException 
03-30 00:56:01.465: E/AndroidRuntime(30155): at java.io.File.<init>(File.java:150) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at java.io.File.<init>(File.java:124) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at tn.pfe.ybn.sigl.MenuAct.onListItemClick(MenuAct.java:97) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.app.ListActivity$2.onItemClick(ListActivity.java:319) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.widget.AdapterView.performItemClick(AdapterView.java:295) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.widget.AbsListView.performItemClick(AbsListView.java:1073) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2577) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.widget.AbsListView$1.run(AbsListView.java:3302) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.os.Handler.handleCallback(Handler.java:605) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.os.Handler.dispatchMessage(Handler.java:92) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.os.Looper.loop(Looper.java:154) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at android.app.ActivityThread.main(ActivityThread.java:4624) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at java.lang.reflect.Method.invokeNative(Native Method) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at java.lang.reflect.Method.invoke(Method.java:511) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576) 
03-30 00:56:01.465: E/AndroidRuntime(30155): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

变化

final Dialog dialog = new Dialog(this); 

到

final Dialog dialog = new Dialog(YourActivity.this); 

只是无论是名字是你的活动取代YourActivity。

编辑：

而且改变

Intent intent = new Intent(this,FileChooser.class); 
startActivity(intent); 

到

Intent intent = new Intent(YourActivity.this,FileChooser.class); 
startActivity(intent); 

Answer 2

您需要提供上下文像这个 - 对话框类> MenuAct.this

@Override 
protected void onListItemClick(ListView l, View v, int position, long id) { 
String item = (String) getListAdapter().getItem(position); 
       if(item.equals("Importer Geotiff")||item.equals("Importer KML")){ 
        { 
        Intent intent = new Intent(this,FileChooser.class); 
          startActivity(intent); 
        }} 
       else if(item.equals("Exporter")) 
       { 
        final Dialog dialog = new Dialog(MenuAct.this); 
        dialog.setContentView(R.layout.dialog_nom_fichier); 
        dialog.setTitle("Nom"); 
        dialog.show(); 
        } 
Toast.makeText(this, item + " selected", Toast.LENGTH_LONG).show(); 
    }