我有一个微调器,它已经包含一些物品。我试图通过setResult和onActivityResult从另一个活动中获取新项目之后添加一个新项目:
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,每次代码运行时,活动都会关闭。显示此异常:
03-29 19:20:30.925 26953-26953 / com.example.user.privatelessons E / AndroidRuntime:FATAL EXCEPTION:main进程:com.example.user.privatelessons,PID:26953 java.lang.RuntimeException:传递结果失败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需要android.app.ActivityThread.deleverResult(ActivityThread.java:4222)的android.app.ActivityThread.deleverResult(ActivityThread.java:4222)处的android.app.ActivityThread.-wrap20(ActivityThread.java)上的消息在android.app.A.运行Android.os.Holer.loop(Looper.java:163)上的android.app.A.运行时,Android.A.运行时,运行android.app.A.运行时,运行android.app.A活动线程(运动转发代码:。 app.ActivityThread.main(ActivityThread.java:6238)at java.lang.reflect.Method.invoke(Native Method)at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:9 04)at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)引起:java.lang.NullPointerException:println需要android.util上android.util.Log.println_native(Native Method)的消息.log.e(Log.java:236)位于android.app的android.app.Activity.dispatchActivityResult(Activity.java:7121)的com.example.user.privatelessons.AddLessonActivity.onActivityResult(AddLessonActivity.java:123)。 ActivityThread.deliverResults(ActivityThread.java:4175)在android.app.ActivityThread.handleSendResult(ActivityThread.java:4222)的android.app.ActivityThread.-wrap20(ActivityThread.java)android.app.ActivityThread $ H.handleMessage( ActivityThread.java:1581)android.app.Handler.dispatchMessage(Handler.java:102)android.app.Looper.loop(Looper.java:163)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()返回String []。
以下代码,只显示logcat中的名称(不将其添加到微调器),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);
}
对于Make List <> Variable,ArrayAdapter全局在onCreate方法之上。 在oncreate方法中添加默认项目,并为该微调器配置Arrayadapter。
然后在onActivityResult中添加List.add(“String”)中的新值。 之后添加此行。 adapter.notifydatasetchanges();它会将您的数据更新为微调控件。
如果需要更多帮助,我会在这里给出附加示例。
您必须将方法db.GetStudentslist()
的输出存储到类(Activity)中的某个字段(列表)。当你想添加/删除/更改元素时,只需修改列表,然后在适配器中更新它。
我创建了简单的例子:
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);
});
}
}
<?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>
如果您在onActivityResult()
中接收数据,则可以采用相同的方式进行:
// Read data
String name = data.getStringExtra("name");
// Add to list
listOfElements.add(name);
记得正确开始活动:
startActivityForResult(intent, GET_NEW_STUDENT_NAME);
如果你想发回数据:
Intent returnIntent = new Intent();
returnIntent.putExtra("name",result);
setResult(Activity.RESULT_OK,returnIntent);
finish();
在你的onActivityResult()
方法中,你必须检查两个条件:
@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);
}
}
}
我终于搞定了。事实证明,这个问题是Unable to modify ArrayAdapter in ListView: UnsupportedOperationException的重复