好的，想象一下。我在页面中动态添加和减少微调器，它们中都有250多个项目，它们是从ArrayList类型的对象的Course对象中获得的，而另一方面ArrayList从TreeMap中获取其值]，因为我需要对其进行排序。现在的问题。我希望有一个小按钮“关于课程”，单击该按钮时，它将显示当前所选课程的弹出窗口，并将视图设置为适当的值（我具有CRN，名称，描述和学分视图）。那么，如何指定要检索微调器上选定对象的对象信息，然后将TextView值设置为该对象呢？ Switch语句不是一种选择，因为我在这里处理大量对象。我正在尝试rn
CRN.setText(courseMap.get(courseSpinner.getSelectedItem()).getCRN());
但是我遇到了崩溃java.lang.ClassCastException: coda759.schedulebuilder2.Course cannot be cast to java.lang.Comparable也尝试过此
CRN.setText(courseMap.get(String.valueOf(courseSpinner.getSelectedItem())).getCRN());
我得到java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
方法：
public void aboutCoursePopup(View v) {
TextView CRN;
TextView name;
TextView credits;
TextView description;
aboutCourse.setContentView(R.layout.about_course_popup);
CRN = findViewById(R.id.crn_popup);
name = findViewById(R.id.name_popup);
credits = findViewById(R.id.credits_popup);
description = findViewById(R.id.desc_popup);
CRN.setText(courseMap.get(String.valueOf(courseSpinner.getSelectedItem())).getCRN());
aboutCourse.show();
//following commented out also causes a crash
// Button btnOk = findViewById(R.id.about_ok);
// btnOk.setOnClickListener(new View.OnClickListener() {
// @Override
// public void onClick(View v) {
// aboutCourse.dismiss();
// }
// });
}
public void aboutCoursePopup(View v) {
TextView CRN;
TextView name;
TextView credits;
TextView description;
aboutCourse.setContentView(R.layout.about_course_popup);
CRN = findViewById(R.id.crn_popup);
name = findViewById(R.id.name_popup);
credits = findViewById(R.id.credits_popup);
description = findViewById(R.id.desc_popup);
//need to setText of CRN, name, description and credits here
aboutCourse.show();
}
此位在onCreate（）方法中
aboutCourse = new Dialog(this);
//about course btn
Button abtCourseBtn = findViewById(R.id.about_course_btn);
abtCourseBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
aboutCoursePopup(v);
}
});
这里是弹出的xml布局
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="400dp"
android:layout_height="wrap_content"
android:padding="10dp"
android:background="@color/colorSecondaryDark"
android:layout_gravity="center">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@color/colorPrimary">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="CRN:"
android:textSize="25sp" />
<TextView
android:id="@+id/crn_popup"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="5"
android:text="PLHXXX"
android:textSize="25sp"
android:layout_marginLeft="38dp"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@color/colorPrimaryDark">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Name:"
android:textSize="25sp"/>
<TextView
android:id="@+id/name_popup"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="3"
android:text="Course Name"
android:textSize="25sp" />
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@color/colorPrimary">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Credits:"
android:textSize="25sp"/>
<TextView
android:id="@+id/credits_popup"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="3"
android:text="X.0"
android:textSize="25sp"/>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:background="@color/colorPrimaryDark">
<TextView
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="2"
android:text="Description:"
android:textSize="25sp"/>
<TextView
android:id="@+id/desc_popup"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="3"
android:text="Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."
android:textSize="20sp"
android:padding="4dp"/>
</LinearLayout>
<Button
android:id="@+id/about_ok"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OK"
android:background="@color/colorPrimary" />
</LinearLayout>
adapter = new ArrayAdapter（getApplicationContext（），android.R.layout.simple_spinner_item，英雄）;categoryspin.setAdapter（adapter）;
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
int selectedItemOfMySpinner = categoryspin.getSelectedItemPosition();
String actualPositionOfMySpinner = (String) categoryspin.getItemAtPosition(selectedItemOfMySpinner);
if (actualPositionOfMySpinner.isEmpty()) {
alertDialogueBox.setSpinnerError(categoryspin, getString(0));
}
categoryspin.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> parent, View view, final int pos, long id) {
if (pos >= 0 && pos < catheroList.size()) {
item = catheroList.get(pos).getId();
Log.e("item", item);
} else {
Toast.makeText(MainActivity.this, "Selected Category Does not Exist!", Toast.LENGTH_SHORT).show();
}