Java 将数据从第二个活动发送到第一个活动不会';机器人不能工作
我目前正在开发一个应用程序,可以让你列出笔记:Java 将数据从第二个活动发送到第一个活动不会';机器人不能工作,java,android,android-intent,Java,Android,Android Intent,我目前正在开发一个应用程序,可以让你列出笔记: 该列表可在第一个活动中查看 “新建注释”按钮将导致第二个活动,其中包含编辑文本和一些文本格式按钮(粗体、斜体、大文本、小文本) 该应用程序允许您长时间单击以编辑或删除列表中的注释 问题是,当我将数据从一个活动发送到另一个活动时,我在日志中发现以下错误: java.lang.NullPointerException:尝试调用虚拟方法 空对象上的“java.lang.String java.lang.Object.toString()” 参考文献
- 该列表可在第一个活动中查看
- “新建注释”按钮将导致第二个活动,其中包含编辑文本和一些文本格式按钮(粗体、斜体、大文本、小文本)
- 该应用程序允许您长时间单击以编辑或删除列表中的注释
getText().toString()
很好用。以下是在活动和之间发送/接收数据的代码以及保存方法
public void sendMessage(View view)
{
editText = (EditText) findViewById(R.id.add_text);
String message = editText.getText().toString();
Intent intent = new Intent(this, MainActivity.class);
intent.putExtra(key_Message, message);
startActivity(intent);
}
@Override
protected void onResume() {
super.onResume();
Intent intent = getIntent();
String message = intent.getStringExtra(key_Message);
list.add(message);
adapter.notifyDataSetChanged();
}
下面是内部保存文本的方法(这很好)。请注意,我在writeMessage中添加了sendMessage函数(但对其进行了注释)
还有一个小问题,我也无法解决:
public void shrinkText(View view)
{ float modifySize = editText.getTextSize();
modifySize = modifySize - 3;
editText.setTextSize(modifySize);
}
是一种小方法,当用户单击按钮时,该方法可以从编辑文本中收缩文本。它总是增加文本。我们将非常感谢您的帮助
public void writeMessage(View view)
{
String Message = editText.getText().toString();
String file_name = "Notes_file";
try {
FileOutputStream fileOutputStream = openFileOutput(file_name, MODE_PRIVATE);
fileOutputStream.write(Message.getBytes());
fileOutputStream.close();
Toast.makeText(getApplicationContext(), "Message has been saved", Toast.LENGTH_SHORT).show();
String message = editText.getText().toString();
Intent intent = new Intent();
intent.putExtra(key_edit, message);
setResult(RESULT_OK, intent);
finish();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == 1){
if(resultCode == RESULT_OK){
String item_tobeadded1;
item_tobeadded1 = data.getStringExtra(key_edit);
list.add(item_tobeadded1);
//adapter.notifyDataSetChanged();
adapter = new ArrayAdapter<String>(this,android.R.layout.simple_expandable_list_item_1, list);
list_view.setAdapter(adapter);
}
}
}
public void writeMessage(视图)
{
String Message=editText.getText().toString();
字符串文件\u name=“Notes\u file”;
试一试{
FileOutputStream FileOutputStream=openFileOutput(文件名,模式\私有);
fileOutputStream.write(Message.getBytes());
fileOutputStream.close();
Toast.makeText(getApplicationContext(),“消息已保存”,Toast.LENGTH\u SHORT.show();
String message=editText.getText().toString();
意图=新意图();
intent.putExtra(按键编辑,信息);
设置结果(结果正常,意图);
完成();
}catch(filenotfounde异常){
e、 printStackTrace();
}捕获(IOE异常){
e、 printStackTrace();
}
}
@凌驾
受保护的void onActivityResult(int请求代码、int结果代码、意图数据){
super.onActivityResult(请求代码、结果代码、数据);
if(requestCode==1){
if(resultCode==RESULT\u OK){
字符串项_应为1;
item_tobeaded1=data.getStringExtra(键编辑);
列表。添加(项目1);
//adapter.notifyDataSetChanged();
adapter=new ArrayAdapter(这是android.R.layout.simple\u expandable\u list\u item\u 1,list);
列表\视图.设置适配器(适配器);
}
}
}
正如前面所建议的那样,您可以使用编辑时刚刚单击的列表视图
项上的数据,或者当您装入新文件时,开始您的第二项活动
通过这种方式,您可以编辑和创建新注释,而无需对代码进行太多更改
int RESPONSE_CODE = 123; // from this code will will differentiate if
// the activity which we started actually did the task or not
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
intent.putString("para1","arg1");
intent.putString("para2","arg2");
intent.putString("para3","arg3");
intent.putString("para4","arg4");
startActivityForResult(intent, RESPONSE_CODE);
}
});
一旦你完成了笔记的创建或编辑,将相关数据附加到意图上,然后像这样完成活动
Intent intent = new Intent();
intent.putExtra("para1","edited_data_1");
intent.putExtra("para2","edited_data_2");
intent.putExtra("para3","edited_data_3");
intent.putExtra("para4","edited_data_4");
setResult(RESULT_OK, intent);
finish();
如果任务成功,您将结果设置为result\u OK
附加意图,您就完成了
在上一个活动中,您必须重写名为onActivityResult()
的方法此方法从您开始执行某些任务的活动接收数据
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 1) {
if(resultCode == RESULT_OK){
String arg1 = data.getStringExtra("para1");
String arg2 = data.getStringExtra("para2");
String arg3 = data.getStringExtra("para3");
String arg4 = data.getStringExtra("para4");
// if you receive the data here,
// you can add another element to List from which the -
//`ListView` is populated and call `notifyDataSetChanged()` on the adapter.
// like this `adapter.notifyDataSetChanged();` it will update the `listview` -
//with new data that you received from the `NoteEditActivity.class`
adapter.notifyDataSetChanged(); // I am assuming you would add the changed item to the List
}
}
}
更新,我已经为您创建了一个虚拟代码,它确实有效,我已经测试过了,我还将它上传到Github上,您可以在那里检查它
NoteListActivity.java
public class NoteListActivity extends Activity {
private ListView listView;
private ArrayList<String> strings;
public static final String NEW_ELEMENT = "NEW_ELEMENT";
public static final String ELEMENT_VALUE = "ELEMENT_VALUE";
public static final String ELEMENT_POSITION = "ELEMENT_POSITION";
private ArrayAdapter<String> adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_note_list);
listView = (ListView) findViewById(R.id.NoteListActivity_listView);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String text = (String) listView.getItemAtPosition(position);
Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
intent.putExtra(NEW_ELEMENT, false);
intent.putExtra(ELEMENT_POSITION, position);
intent.putExtra(ELEMENT_VALUE, text);
startActivityForResult(intent, 123);
}
});
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.NoteListActivity_fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getApplicationContext(), NoteEditActivity.class);
intent.putExtra(NEW_ELEMENT, true);
startActivityForResult(intent, 123);
}
});
setUpList();
adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.simple_list_item_1, strings);
listView.setAdapter(adapter);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
Log.d("NoteListActivity1",""+data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
if (requestCode == 123) {
if (resultCode == RESULT_OK) {
Log.d("NoteListActivity2",""+data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
boolean isNewElement = data.getBooleanExtra(NoteListActivity.NEW_ELEMENT, false);
if (isNewElement) {
strings.add("" + data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
adapter.notifyDataSetChanged();
} else {
strings.set(data.getIntExtra(NoteListActivity.ELEMENT_POSITION, 0), "" + data.getStringExtra(NoteListActivity.ELEMENT_VALUE));
adapter.notifyDataSetChanged();
}
}
}
}
private void setUpList() {
strings = new ArrayList<>();
for (int i = 0; i < 4; i++) {
strings.add("Element_1_" + i);
}
}
}
public class NoteEditActivity extends Activity {
private EditText editText;
private Button button;
private boolean isNewElement;
private int position;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_note_edit);
editText = (EditText) findViewById(R.id.NoteEditActivity_editText);
button = (Button) findViewById(R.id.NoteEditActivity_button);
Intent myIntent = getIntent();
isNewElement = myIntent.getBooleanExtra(NoteListActivity.NEW_ELEMENT, false);
if (!isNewElement) {
editText.setText("" + myIntent.getStringExtra(NoteListActivity.ELEMENT_VALUE));
position = myIntent.getIntExtra(NoteListActivity.ELEMENT_POSITION,0);
}
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String text = editText.getText().toString();
if (text != null && text.trim().length() > 0) {
Intent intent = new Intent();
Log.d("NoteEditActivity",""+text);
intent.putExtra(NoteListActivity.ELEMENT_VALUE, text);
intent.putExtra(NoteListActivity.NEW_ELEMENT, isNewElement);
if (!isNewElement) {
intent.putExtra(NoteListActivity.ELEMENT_POSITION, position);
}
setResult(RESULT_OK, intent);
finish();
} else {
Toast.makeText(getApplicationContext(), "Kindly write a valid element name", Toast.LENGTH_SHORT).show();
}
}
});
}
}
活动\u注释\u edit.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.nimgade.pk.mytutorialapplication.MainActivity">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="activities.list.first.NoteListActivity">
<ListView
android:id="@+id/NoteListActivity_listView"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>
<android.support.design.widget.FloatingActionButton
android:id="@+id/NoteListActivity_fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_menu_add" />
</android.support.design.widget.CoordinatorLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical"
tools:context="activities.list.first.NoteEditActivity">
<EditText
android:id="@+id/NoteEditActivity_editText"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/NoteEditActivity_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Save"
android:textAllCaps="false" />
</LinearLayout>
这是一个很好的答案,可以帮助您实现您的逻辑。发送现在可以工作,但当我将特定项添加到listview时,它不会出现。请调用列表视图的适配器,并在发送对象时调用notifyDataSetChanged。确实如此。。。否则我就不可能在这里了。。但它仍然不会将项目添加到列表中,我使用list.add(item)和adapter.notifyDataSetChanged()@user3402719 ok,在这种情况下,将项目添加到列表后重新启动适配器,并将此适配器设置为listviewStill nothing。。。我添加该项,然后重新初始化适配器,并将其重新设置为用于listLast代码块。它发送数据,不会将其添加到列表中。您的列表是否为字符串类型?
public class NoteEditActivity extends Activity {
private EditText editText;
private Button button;
private boolean isNewElement;
private int position;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_note_edit);
editText = (EditText) findViewById(R.id.NoteEditActivity_editText);
button = (Button) findViewById(R.id.NoteEditActivity_button);
Intent myIntent = getIntent();
isNewElement = myIntent.getBooleanExtra(NoteListActivity.NEW_ELEMENT, false);
if (!isNewElement) {
editText.setText("" + myIntent.getStringExtra(NoteListActivity.ELEMENT_VALUE));
position = myIntent.getIntExtra(NoteListActivity.ELEMENT_POSITION,0);
}
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String text = editText.getText().toString();
if (text != null && text.trim().length() > 0) {
Intent intent = new Intent();
Log.d("NoteEditActivity",""+text);
intent.putExtra(NoteListActivity.ELEMENT_VALUE, text);
intent.putExtra(NoteListActivity.NEW_ELEMENT, isNewElement);
if (!isNewElement) {
intent.putExtra(NoteListActivity.ELEMENT_POSITION, position);
}
setResult(RESULT_OK, intent);
finish();
} else {
Toast.makeText(getApplicationContext(), "Kindly write a valid element name", Toast.LENGTH_SHORT).show();
}
}
});
}
}
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical"
tools:context="activities.list.first.NoteEditActivity">
<EditText
android:id="@+id/NoteEditActivity_editText"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="@+id/NoteEditActivity_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Save"
android:textAllCaps="false" />
</LinearLayout>