英文:
Clicking the button to second activity automatically closes app [Android Studio]
问题
以下是翻译好的部分:
Background
只是为了提供一些背景信息,我对Android应用程序开发非常陌生。在使用Android开发者指南开发一个教我如何创建一个“Hello, World!”项目的基本应用程序之后,我尝试学习如何构建用户界面并启动另一个活动。最终,主要关注的是在MainActivity中添加一些代码,以在用户点击“发送”按钮时启动一个新的活动来显示一条消息。在将应用程序运行在我的设备上之后,我尝试输入一条消息并点击发送,但发送按钮最终关闭了我的应用程序,没有任何延迟,也没有解释为什么关闭了应用程序。
MainActivity.java
package com.example.giglitz;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import static android.provider.AlarmClock.EXTRA_MESSAGE;
public class MainActivity extends AppCompatActivity {
public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
/** Called when the user taps the send button */
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.editText);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
}
AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.giglitz">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".DisplayMessageActivity">
android:parentActivityName=".MainActivity">
<!-- 如果您支持API级别为15或更低级别,则需要meta-data标签 -->
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value=".MainActivity" />
</activity>
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
DisplayMessageActivity.java
package com.example.giglitz;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
public class DisplayMessageActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_message);
// 获取启动此活动的Intent并提取字符串
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
// 获取布局的TextView并将字符串设置为其文本
TextView textView = findViewById(R.id.textView);
textView.setText(message);
}
}
activity_display_message.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".DisplayMessageActivity">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:text="TextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Logcat(在过滤错误后,只显示选定应用程序)
Process: com.example.giglitz, PID: 6422
java.lang.IllegalStateException: Could not execute method for android:onClick
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:402)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.example.giglitz.MainActivity.sendMessage(MainActivity.java:24)
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
<details>
<summary>英文:</summary>
## **Background** ##
Just to set some context, I'm very new to Android app development. After using Android Developers guide on developing a basic app that would teach me how to create a "Hello, World!" project. However, after learning to build a user interface and start another activity. Ultimately, the main focus was to add some code to the MainActivity that starts a new activity to display a message when the user would tap the Send button. After running the app on my device, I attempted to type out a message and click send, only for the send button to ultimately close my app with no lag, or explaination as to why it closed.
**MainActivity.java**
package com.example.giglitz;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import static android.provider.AlarmClock.EXTRA_MESSAGE;
public class MainActivity extends AppCompatActivity {
public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
/** Called when the user taps the send button */
public void sendMessage(View view) {
Intent intent = new Intent(this, DisplayMessageActivity.class);
EditText editText = (EditText) findViewById(R.id.editText);
String message = editText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);
}
}
**AndroidManifest.xml**
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.giglitz">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".DisplayMessageActivity">
android:parentActivityName=".MainActivity">
<!-- The meta-data tag is required if you support API level 15 and lower -->
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value=".MainActivity" />
</activity>
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
**DisplayMessageActivity.java**
package com.example.giglitz;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;
public class DisplayMessageActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_message);
// Get the Intent that started this activity and extract the string
Intent intent = getIntent();
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
// Capture the layout's TextView and set the string as its text
TextView textView = findViewById(R.id.textView);
textView.setText(message);
}
}
**activity_display_message.xml**
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".DisplayMessageActivity">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:text="TextView"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
**Logcat (after filtering Error, Show only selected application)**
Process: com.example.giglitz, PID: 6422
java.lang.IllegalStateException: Could not execute method for android:onClick
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:402)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.example.giglitz.MainActivity.sendMessage(MainActivity.java:24)
at java.lang.reflect.Method.invoke(Native Method)
at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
at android.view.View.performClick(View.java:7201)
at android.view.View.performClickInternal(View.java:7170)
at android.view.View.access$3500(View.java:806)
at android.view.View$PerformClick.run(View.java:27562)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7682)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)
**activity_main.xml**
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<EditText
android:id="@+id/editTextTextPersonName"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:ems="10"
android:hint="@string/edit_message"
android:inputType="textPersonName"
app:layout_constraintEnd_toStartOf="@+id/button"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:onClick="sendMessage"
android:text="@string/button_send"
app:layout_constraintBaseline_toBaselineOf="@+id/editTextTextPersonName"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toEndOf="@+id/editTextTextPersonName" />
</androidx.constraintlayout.widget.ConstraintLayout>
</details>
# 答案1
**得分**: 1
我认为你要么没有在按钮的 'onclick' 字段中放入任何内容,要么没有为你的 EditText 设置ID。你能发送你的 activity_main.xml 文件吗?如果你想知道它在哪里,进入 'res' 目录,然后进入 'layout' 目录。
<details>
<summary>英文:</summary>
I think you either did not put anything in the 'onclick' field for your button, or you didn't set an ID for your EditText. Can you send your activity_main.xml file as well? If you want to know where it is, go to the 'res' directory, and then go into the 'layout' directory.
</details>
# 答案2
**得分**: 0
我需要查看您的日志输出以确定您遇到了什么问题。通常在使用意图附加信息(Intent extras)时,我建议检查对象的可为null性,因为该字符串可能不存在,尽管在这种情况下它显然是存在的。所以,请发送您日志的文字记录。谢谢!
<details>
<summary>英文:</summary>
I will need to see your logcat output to determine what problems you encountered. Generally, when using Intent extras, I recommend checking for nullability of objects, as that string might not exist, although it clearly does in this case. So, please send a transcript of your logs.
Thanks!
</details>
# 答案3
**得分**: 0
好的,以下是您要翻译的内容:
看起来您在应用程序中没有正确实现“onclick”行为。在 XML 文件中,您应该为发送按钮添加这一行:`android:onClick="sendMessage"`
另外,查看以下链接以获取有关在 Android 中实现 onClick 行为的更多详细信息:https://developer.android.com/guide/topics/ui/controls/button#HandlingEvents,https://stackoverflow.com/a/4153842/1725535
<details>
<summary>英文:</summary>
It looks like you did not implement the 'onclick' behavior correctly in your app. In the XML file, you should add this line for your send button `android:onClick="sendMessage"`
Also, check out this for more details about implementing onClick behaviors in Android: https://developer.android.com/guide/topics/ui/controls/button#HandlingEvents, https://stackoverflow.com/a/4153842/1725535
</details>
# 答案4
**得分**: 0
看起来你在应用程序中没有正确实现 'onclick' 行为。在 XML 文件中,你应该为发送按钮添加这一行代码 android:onClick="sendMessage"
这样可以让活动监听按钮点击事件并调用 onClickListener 方法。
<details>
<summary>英文:</summary>
It looks like you did not implement the 'onclick' behavior correctly in your app. In the XML file, you should add this line for your send button android:onClick="sendMessage"
To tell activity to listen the button click and call the onClickListner method.
</details>
# 答案5
**得分**: 0
代码部分不要翻译,只返回翻译好的内容:
似乎您在应用程序中没有正确实现'onclick'行为。在XML文件中,您应该为发送按钮添加这行代码android:onClick="sendMessage",或者您可以通过按钮ID以编程方式使用它。例如:
```java
Button btn = (Button) findViewById(R.id.sendButton);
btn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// 在这里添加您的语句
}
});
通过这种方式,您可以告诉活动监听按钮点击事件并调用onClickListner方法。
英文:
It looks like you did not implement the 'onclick' behavior correctly in your app.
In the XML file, you should add this line for your send button
android:onClick="sendMessage" or you can use it programmatically by button id
For eg:-
Button btn = (Button) findViewById(R.Id.sendButton);
btn.setOnClickListner(new View.OnClickListner){
@Override
public onClick(View view){
// Your statement
}
}
To tell activity to listen the button click and call the onClickListner method.
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