Android - popUpWindow 中的 DatePicker

Question

我正在尝试在弹出窗口中显示日期选择器。当用户单击弹出窗口中的“选择日期”按钮时，应该显示日历。问题是我收到一个 NullPointerException ，因为显然我的 button 为空，我不明白为什么。

这是我的主要 Activity :

private void popUpWindow2() {
        LayoutInflater layoutInflater = LayoutInflater.from(MarkerActivity.this);
        View promptView2 = layoutInflater.inflate(R.layout.input_journey, null);
        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(MarkerActivity.this);
        alertDialogBuilder.setView(promptView2);

        button = (Button) findViewById(R.id.button_pick);
        button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                showDialog(DATE_DIALOG_ID);

            }

        });

        // setup a dialog window
        alertDialogBuilder.setCancelable(false)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int id) {
                        String msg3 = "The POI has been added to your journey on " + day + "-" + month+1 + "-" + year;
                        Toast.makeText(getApplicationContext(), msg3, Toast.LENGTH_LONG).show();
                    }

                })
                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });

        // create an alert dialog
        AlertDialog alert = alertDialogBuilder.create();
        alert.show();
    }

    @Override
    public Dialog onCreateDialog(int id) {

        switch (id) {
            case DATE_DIALOG_ID:
                // set date picker as current date
                return new DatePickerDialog(this, datePickerListener, year, month,day);
        }
        return null;
    }

    public DatePickerDialog.OnDateSetListener datePickerListener = new DatePickerDialog.OnDateSetListener() {

        // when dialog box is closed, below method will be called.
        public void onDateSet(DatePicker view, int selectedYear,int selectedMonth, int selectedDay) {
            year = selectedYear;
            month = selectedMonth;
            day = selectedDay;
        }
    };

input_journey.xml

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="10dp">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:layout_below="@+id/edittext1"
        android:text="Would you like to add this POI to your journey?"
        android:id="@+id/add_to_journey" />

    <Button
        android:id="@+id/button_pick"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Pick a date!" />

</LinearLayout>

我的日志猫:

08-04 20:52:07.748    3552-3552/com.example.diana.track E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.NullPointerException
            at com.example.diana.track.MarkerActivity.popUpWindow2(MarkerActivity.java:457)
            at com.example.diana.track.MarkerActivity.access$000(MarkerActivity.java:51)
            at com.example.diana.track.MarkerActivity$3.onClick(MarkerActivity.java:123)
            at android.view.View.performClick(View.java:4421)
            at android.view.View$PerformClick.run(View.java:17903)
            at android.os.Handler.handleCallback(Handler.java:730)
            at android.os.Handler.dispatchMessage(Handler.java:92)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5214)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:525)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
            at dalvik.system.NativeStart.main(Native Method)

知道可能出了什么问题吗？

Answer 1

您的按钮位于您正在使用(input_journey.xml)填充弹出窗口的 View 上，而您引用该按钮就像它是另一个 View 的一部分一样，因此无法访问.

在弹出窗口 View 中访问该按钮，如下所示:

button = (Button) promptView2.findViewById(R.id.button_pick);

请注意，您声明的 View promptView2 是按钮的父 View 。