如何将单个项目添加到现有微调器？
How to add a single item to an existing spinner?
我有一个微调器，其中已经包含了一些项目。在通过 setResult 和 onActivityResult:
从另一个 activity 获取新项目后，我试图向其中添加一个新项目
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && null
{...}
else if(requestCode == GET_NEW_STUDENT_NAME)
{
String name = data.getStringExtra("name");
ArrayAdapter<String> adapter = (ArrayAdapter<String>)studentsSpinner.getAdapter();
adapter.add(name);
studentsSpinner.setAdapter(adapter);
}
}
但是，每次运行代码时，activity 都会关闭。正在显示此异常：
03-29 19:20:30.925 26953-26953/com.example.user.privatelessons E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.user.privatelessons, PID: 26953
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=2, result=-1, data=Intent { (has extras) }} to activity {com.example.user.privatelessons/com.example.user.privatelessons.AddLessonActivity}: java.lang.NullPointerException: println needs a message
at android.app.ActivityThread.deliverResults(ActivityThread.java:4179)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:4222)
at android.app.ActivityThread.-wrap20(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1581)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:163)
at android.app.ActivityThread.main(ActivityThread.java:6238)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
Caused by: java.lang.NullPointerException: println needs a message
at android.util.Log.println_native(Native Method)
at android.util.Log.e(Log.java:236)
at com.example.user.privatelessons.AddLessonActivity.onActivityResult(AddLessonActivity.java:123)
at android.app.Activity.dispatchActivityResult(Activity.java:7121)
at android.app.ActivityThread.deliverResults(ActivityThread.java:4175)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:4222)
at android.app.ActivityThread.-wrap20(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1581)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:163)
at android.app.ActivityThread.main(ActivityThread.java:6238)
[编辑]：开始时，我使用以下代码初始化微调器：
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, db.GetStudentslist());;
spinner.setAdapter(adapter);
GetStudentslist() returns String[].
以下代码仅在 logcat 中显示名称（未将其添加到微调器），工作正常：
if(requestCode == GET_NEW_STUDENT_NAME && data != null)
{
String name = data.getStringExtra("name");
/* List<String> names = Arrays.asList(db.GetStudentslist());
names.add(name);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, names);;
studentsSpinner.setAdapter(adapter);*/
Log.e("Name", name);
}
您必须将方法 db.GetStudentslist() 的输出存储到 class (Activity) 中的某个字段（列表）中。当您想要 add/remove/change 元素时，只需修改列表，并在适配器中更新它。
我创建了一个简单的例子：
Activity
package training.com.myapplication;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class MainActivity extends AppCompatActivity {
// List with three predefined elements
private List<String> listOfElements = new ArrayList<>(Arrays.asList(
"Hello world", "Hello world", "Hello world"
));
// Adapter for the Spinner
private ArrayAdapter<String> adapter;
private Spinner spinner;
private Button addButton;
private Button removeButton;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initialize adapter
adapter = new ArrayAdapter<>(this,
android.R.layout.simple_spinner_item, listOfElements);
spinner = findViewById(R.id.action_bar_spinner);
addButton = findViewById(R.id.add_button);
removeButton = findViewById(R.id.remove_button);
// Set adapter
spinner.setAdapter(adapter);
addButton.setOnClickListener(view -> {
// Add new element to the list
listOfElements.add("Hello world");
});
removeButton.setOnClickListener(view -> {
// Remove last item from the list
int lastIndex = listOfElements.size() - 1;
listOfElements.remove(lastIndex);
});
}
}
布局简单：
<?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="match_parent"
android:layout_margin="40dp"
android:orientation="vertical">
<Spinner
android:id="@+id/action_bar_spinner"
android:layout_width="match_parent"
android:layout_height="50dp" />
<Button
android:id="@+id/add_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="+"
android:textSize="30sp" />
<Button
android:id="@+id/remove_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="-"
android:textSize="30sp" />
</LinearLayout>
预期输出
如果您在 onActivityResult() 中接收数据，您可以采用相同的方式：
// Read data
String name = data.getStringExtra("name");
// Add to list
listOfElements.add(name);
记得正确启动activity：
startActivityForResult(intent, GET_NEW_STUDENT_NAME);
如果您想发回数据：
Intent returnIntent = new Intent();
returnIntent.putExtra("name",result);
setResult(Activity.RESULT_OK,returnIntent);
finish();
并且在您的 onActivityResult() 方法中您必须检查两个条件：
@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
// Check result
if (resultCode == Activity.RESULT_OK) {
// And check what was requested
if (requestCode == GET_NEW_STUDENT_NAME) {
String name = data.getStringExtra("name");
listOfElements.add(name);
}
}
}
我终于让它工作了。原来这个问题和Unable to modify ArrayAdapter in ListView: UnsupportedOperationException
重复了
为此使List<>变量，ArrayAdapter全局在onCreate方法之上。
在 oncreate 方法中添加默认项并为该微调器配置 Arrayadapter。
然后在 onActivityResult 中添加 List.add("String") 中的新值。
之后添加这一行。
adapter.notifydatasetchanges();
它会将您的数据更新到微调器控件中。
如果需要更多帮助，我会在这里给出附加示例。
我有一个微调器，其中已经包含了一些项目。在通过 setResult 和 onActivityResult:
从另一个 activity 获取新项目后，我试图向其中添加一个新项目 protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == RESULT_LOAD_IMAGE && resultCode == RESULT_OK && null
{...}
else if(requestCode == GET_NEW_STUDENT_NAME)
{
String name = data.getStringExtra("name");
ArrayAdapter<String> adapter = (ArrayAdapter<String>)studentsSpinner.getAdapter();
adapter.add(name);
studentsSpinner.setAdapter(adapter);
}
}
但是，每次运行代码时，activity 都会关闭。正在显示此异常：
03-29 19:20:30.925 26953-26953/com.example.user.privatelessons E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.user.privatelessons, PID: 26953 java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=2, result=-1, data=Intent { (has extras) }} to activity {com.example.user.privatelessons/com.example.user.privatelessons.AddLessonActivity}: java.lang.NullPointerException: println needs a message at android.app.ActivityThread.deliverResults(ActivityThread.java:4179) at android.app.ActivityThread.handleSendResult(ActivityThread.java:4222) at android.app.ActivityThread.-wrap20(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1581) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:163) at android.app.ActivityThread.main(ActivityThread.java:6238) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794) Caused by: java.lang.NullPointerException: println needs a message at android.util.Log.println_native(Native Method) at android.util.Log.e(Log.java:236) at com.example.user.privatelessons.AddLessonActivity.onActivityResult(AddLessonActivity.java:123) at android.app.Activity.dispatchActivityResult(Activity.java:7121) at android.app.ActivityThread.deliverResults(ActivityThread.java:4175) at android.app.ActivityThread.handleSendResult(ActivityThread.java:4222) at android.app.ActivityThread.-wrap20(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1581) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:163) at android.app.ActivityThread.main(ActivityThread.java:6238)
[编辑]：开始时，我使用以下代码初始化微调器：
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, db.GetStudentslist());;
spinner.setAdapter(adapter);
GetStudentslist() returns String[].
以下代码仅在 logcat 中显示名称（未将其添加到微调器），工作正常：
if(requestCode == GET_NEW_STUDENT_NAME && data != null)
{
String name = data.getStringExtra("name");
/* List<String> names = Arrays.asList(db.GetStudentslist());
names.add(name);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, names);;
studentsSpinner.setAdapter(adapter);*/
Log.e("Name", name);
}
您必须将方法 db.GetStudentslist() 的输出存储到 class (Activity) 中的某个字段（列表）中。当您想要 add/remove/change 元素时，只需修改列表，并在适配器中更新它。
我创建了一个简单的例子：
Activity
package training.com.myapplication;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class MainActivity extends AppCompatActivity {
// List with three predefined elements
private List<String> listOfElements = new ArrayList<>(Arrays.asList(
"Hello world", "Hello world", "Hello world"
));
// Adapter for the Spinner
private ArrayAdapter<String> adapter;
private Spinner spinner;
private Button addButton;
private Button removeButton;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initialize adapter
adapter = new ArrayAdapter<>(this,
android.R.layout.simple_spinner_item, listOfElements);
spinner = findViewById(R.id.action_bar_spinner);
addButton = findViewById(R.id.add_button);
removeButton = findViewById(R.id.remove_button);
// Set adapter
spinner.setAdapter(adapter);
addButton.setOnClickListener(view -> {
// Add new element to the list
listOfElements.add("Hello world");
});
removeButton.setOnClickListener(view -> {
// Remove last item from the list
int lastIndex = listOfElements.size() - 1;
listOfElements.remove(lastIndex);
});
}
}
布局简单：
<?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="match_parent"
android:layout_margin="40dp"
android:orientation="vertical">
<Spinner
android:id="@+id/action_bar_spinner"
android:layout_width="match_parent"
android:layout_height="50dp" />
<Button
android:id="@+id/add_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="+"
android:textSize="30sp" />
<Button
android:id="@+id/remove_button"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:text="-"
android:textSize="30sp" />
</LinearLayout>
预期输出
如果您在 onActivityResult() 中接收数据，您可以采用相同的方式：
// Read data
String name = data.getStringExtra("name");
// Add to list
listOfElements.add(name);
记得正确启动activity：
startActivityForResult(intent, GET_NEW_STUDENT_NAME);
如果您想发回数据：
Intent returnIntent = new Intent();
returnIntent.putExtra("name",result);
setResult(Activity.RESULT_OK,returnIntent);
finish();
并且在您的 onActivityResult() 方法中您必须检查两个条件：
@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
// Check result
if (resultCode == Activity.RESULT_OK) {
// And check what was requested
if (requestCode == GET_NEW_STUDENT_NAME) {
String name = data.getStringExtra("name");
listOfElements.add(name);
}
}
}
我终于让它工作了。原来这个问题和Unable to modify ArrayAdapter in ListView: UnsupportedOperationException
重复了为此使List<>变量，ArrayAdapter全局在onCreate方法之上。
在 oncreate 方法中添加默认项并为该微调器配置 Arrayadapter。
然后在 onActivityResult 中添加 List.add("String") 中的新值。
之后添加这一行。
adapter.notifydatasetchanges();
它会将您的数据更新到微调器控件中。
如果需要更多帮助，我会在这里给出附加示例。