弹出窗口中 ArrayList 的 SetText NullPointerException。 Android

Question

我想在弹出窗口的 TextView 中显示数组 window。阵列中只有 1 个项目随机。在这种情况下，我在 MainActivity 中使用 ArrayList 并调用 randomArray() 进行显示。它不适用于 Screen_popup.xml。但它确实适用于 Main_activity.xml。我使用 TextView textView1 作为 main_activity 和 TextView txtViewArrayContent 作为弹出窗口 window。我认为 TextView 已正确初始化但与 setContentView 有关？任何指点都会很好，谢谢！

log cat 中的错误是：

07-17 09:25:34.655  25779-25779/com.example.testarray_02 E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.testarray_02, PID: 25779
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testarray_02/com.example.testarray_02.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

主要ActivityJava:

public class MainActivity extends Activity {

Button btnClosePopup;
Button btnCreatePopup;
TextView newArray;
String item;

//***** Random Generator & ArrayList *****
final Random randomGenerator = new Random();
final ArrayList sample = new ArrayList() {{ add("Random Facts about Stuff"); add("Random Facts about Stuff 2"); add("Random Facts about Stuff 3"); add("Random Facts about Stuff 4");}};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //Works - main activity layout
   // newArray = (TextView)findViewById(R.id.textView1);

    // Does NOT work. ... popup layout
    newArray = (TextView)findViewById(R.id.txtViewArrayContent);

    randomArray();
    btnCreatePopup = (Button) findViewById(R.id.button1);
    btnCreatePopup.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            customPopupWindow(v);
        }
    });
}

private void randomArray() {
    //setContentView(R.layout.screen_popup);
    item = (String) sample.get(randomGenerator.nextInt(sample.size()));
    newArray.setText(item);  // Error logcat points to this line
                             // Null Exception Error
}
private PopupWindow popupWin;
private void customPopupWindow(View v){
    try {
        LayoutInflater inflater = (LayoutInflater) MainActivity.this
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View layout = inflater.inflate(R.layout.screen_popup,
                (ViewGroup) findViewById(R.id.popup_element));
        popupWin = new PopupWindow(layout, 600, 600, true);
        popupWin.showAtLocation(layout, Gravity.CENTER, 0, 0);
        btnClosePopup = (Button) layout.findViewById(R.id.btn_close_popup);
        btnClosePopup.setOnClickListener(cancel_button_click_listener);
    } catch (Exception e) {
        e.printStackTrace();
    }
}
private View.OnClickListener cancel_button_click_listener = new View.OnClickListener() {
    public void onClick(View v) {
        popupWin.dismiss();
    }
};
}

XML 屏幕弹出窗口的片段

    <TextView
    android:id="@+id/txtViewArrayContent"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="5sp"
    android:text="" />

Answer 1

您正试图通过在 activity_main.xml 文件中通过 ID 找到它来初始化 newArray，但它不存在，所以您得到 NullPointerException。要修复您的代码，请从 onCreate() 方法中删除 newArray 初始化和调用 randomArray() 并将其添加到 customPopupWindwo(View v) 中，如下所示：

private void customPopupWindow(View v) {
    LayoutInflater inflater = (LayoutInflater) MainActivity.this
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View layout = inflater.inflate(R.layout.screen_popup,
            (ViewGroup) findViewById(R.id.popup_element));
    newArray = (TextView) layout.findViewById(R.id.txtViewArrayContent);
    //omitted rest for brevity
}

弹出窗口中 ArrayList 的 SetText NullPointerException。 Android

SetText NullPointerException for ArrayList in PopupWindow. Android

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