应用程序在 listview.getSelectedItem() 时崩溃（Dialog 中的 ListView）Android

Question

我有一个对话框屏幕，在对话框中我有一个列表视图。我想通过吐司消息显示从列表视图中单击了哪个项目。因此，我尝试使用 listview.getSelectedItem().toString() 通过吐司消息显示被单击项目的消息，但在单击列表项时它崩溃了。但是，如果在列表视图中单击某个项目时，我只是按 toast 显示一个字符串，则不会发生崩溃。例如：

Toast.makeText(MainActivity.this, "Hello World", Toast.LENGTH_LONG).show();

但是在下面的代码中崩溃了：

private void showDialer()
{
    //DIALOG SCREEN
    final Dialog dialog = new Dialog(ActionModes.this);
    dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);

    dialog.setContentView(R.layout.dialer_dialog);

    final ListView book_list = (ListView)dialog.findViewById(R.id.listBooks);
    ArrayAdapter<?> adapter_booklist = ArrayAdapter.createFromResource(
            this, R.array.locations, android.R.layout.simple_spinner_item);
            adapter_booklist.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            book_list.setAdapter(adapter_booklist);  

            book_list.setOnItemClickListener(new OnItemClickListener() 
            {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position,
                        long id)
                {
                    Toast.makeText(MainActivity.this, book_list.getSelectedItem().toString(), Toast.LENGTH_LONG).show();
                }
            });              
    dialog.show();   
}

LOGCAT

06-02 23:53:34.521: I/class com.actionbarsherlock.sample.demos.ExternalDbOpenHelper(8581): Database already exists 06-02 23:53:35.321: W/KeyCharacterMap(8581): No keyboard for id -1 06-02 23:53:35.321: W/KeyCharacterMap(8581): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 06-02 23:53:41.291: W/dalvikvm(8581): threadid=1: thread exiting with uncaught exception (group=0x2aac8830) 06-02 23:53:41.291: E/AndroidRuntime(8581): FATAL EXCEPTION: main 06-02 23:53:41.291: E/AndroidRuntime(8581): java.lang.NullPointerException 06-02 23:53:41.291: E/AndroidRuntime(8581): at com.actionbarsherlock.sample.demos.ActionModes.onItemClick(ActionModes.java:87) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.widget.AdapterView.performItemClick(AdapterView.java:284) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.widget.ListView.performItemClick(ListView.java:3382) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.widget.AbsListView$PerformClick.run(AbsListView.java:1702) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.os.Handler.handleCallback(Handler.java:587) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.os.Handler.dispatchMessage(Handler.java:92) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.os.Looper.loop(Looper.java:123) 06-02 23:53:41.291: E/AndroidRuntime(8581): at android.app.ActivityThread.main(ActivityThread.java:4627) 06-02 23:53:41.291: E/AndroidRuntime(8581): at java.lang.reflect.Method.invokeNative(Native Method) 06-02 23:53:41.291: E/AndroidRuntime(8581): at java.lang.reflect.Method.invoke(Method.java:521) 06-02 23:53:41.291: E/AndroidRuntime(8581): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:876) 06-02 23:53:41.291: E/AndroidRuntime(8581): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:634) 06-02 23:53:41.291: E/AndroidRuntime(8581): at dalvik.system.NativeStart.main(Native Method)

Answer 1

通常，当您单击列表视图中的项目时，它不会立即将其状态更改为已选择。您应该通过以下方式获取该项目：

book_list.getItemAtPosition(position)

Answer 2

一方面，检查 book_list.getSelectedItem() 是否为 null。

接下来你想做一个 book_list.getItemAtPosition(pos)

应用程序在 listview.getSelectedItem() 时崩溃（Dialog 中的 ListView）Android

App crashed on listview.getSelectedItem() (ListView inside Dialog) Android

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dialog