英文:
Trying to get a button to load another activity however the is OnClickListner crashing the app
问题
当点击注册按钮时，应用程序应加载另一个活动，但实际上它只会崩溃。尝试在这里1和这里2寻求帮助，但仍然无法解决。我还尝试了删除'implements View.OnClickListener'，并按照示例中显示的方式使用它，但没有成功。还尝试将xml文件更改为LinearLayout，但也没有成功。提前致谢！
public class LogInActivity extends AppCompatActivity implements View.OnClickListener {
// 用户输入变量
EditText emailAddressInput;
EditText passwordInput;
Button logInButton;
Button registerButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// 将布局设置为activity_login.xml
setContentView(R.layout.activity_login);
// 获取用户输入并设置到变量中
emailAddressInput = (EditText)findViewById(R.id.emailAddressInput);
passwordInput = (EditText)findViewById(R.id.passwordInput);
logInButton = (Button)findViewById(R.id.logInButton);
registerButton = (Button)findViewById(R.id.registerButton);
logInButton.setOnClickListener(this);
registerButton.setOnClickListener(this);
}
@Override
public void onClick(View view) {
Intent registerIntent = new Intent (LogInActivity.this, RegisterActivity.class);
switch (view.getId()) {
case R.id.logInButton:
break;
case R.id.registerButton:
startActivity(registerIntent);
break;
}
}
}
编辑：
logcat日志：
2020-04-04 16:02:10.759 12718-12718/com.example.blooddonorsystem E/AndroidRuntime: 致命异常：主线程
进程：com.example.blooddonorsystem，PID：12718
java.lang.RuntimeException：无法启动活动ComponentInfo{com.example.blooddonorsystem/com.example.blooddonorsystem.RegisterActivity}：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)'
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
导致原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)'
at com.example.blooddonorsystem.RegisterActivity.onCreate(RegisterActivity.java:56)
at android.app.Activity.performCreate(Activity.java:7825)
at android.app.Activity.performCreate(Activity.java:7814)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)。
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)。
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)。
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)。
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)。
at android.os.Handler.dispatchMessage(Handler.java:107)。
at android.os.Looper.loop(Looper.java:214)。
at android.app.ActivityThread.main(ActivityThread.java:7356)。
at java.lang.reflect.Method.invoke(Native Method)。
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)。
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)。
<details>
<summary>英文:</summary>
When the register button is clicked the app should load another activity however it just crashes. Tried looking [here][1] and [here][2] for help but I still couldn't fix it. I also tried removing 'implements View.OnClickListner' and using it how its shown in the examples and it didn't work. Also tried changing the xml file to a LinearLayout and that didn't work either. Thanks in advance!
public class LogInActivity extends AppCompatActivity implements View.OnClickListener {
//user input variables
EditText emailAddressInput;
EditText passwordInput;
Button logInButton;
Button registerButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//set the layout to activity_login.xml
setContentView(R.layout.activity_login);
//get user inputs and set to the variables
emailAddressInput = (EditText)findViewById(R.id.emailAddressInput);
passwordInput = (EditText)findViewById(R.id.passwordInput);
logInButton = (Button)findViewById(R.id.logInButton);
registerButton = (Button)findViewById(R.id.registerButton);
logInButton.setOnClickListener(this);
registerButton.setOnClickListener(this);
}
@Override
public void onClick(View view) {
Intent registerIntent = new Intent (LogInActivity.this,RegisterActivity.class);
switch (view.getId())
{
case R.id.logInButton:
break;
case R.id.registerButton:
startActivity(registerIntent);
break;
}
}
}
EDIT:
the logcat:
2020-04-04 16:02:10.759 12718-12718/com.example.blooddonorsystem E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.blooddonorsystem, PID: 12718
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.blooddonorsystem/com.example.blooddonorsystem.RegisterActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
at com.example.blooddonorsystem.RegisterActivity.onCreate(RegisterActivity.java:56)
at android.app.Activity.performCreate(Activity.java:7825)
at android.app.Activity.performCreate(Activity.java:7814)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
at android.os.Handler.dispatchMessage(Handler.java:107) 
at android.os.Looper.loop(Looper.java:214) 
at android.app.ActivityThread.main(ActivityThread.java:7356) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
[1]: http://Intent%20registerIntent%20=%20new%20Intent%20(LogInActivity.this,RegisterActivity.class);
[2]: https://stackoverflow.com/questions/58830966/android-why-does-my-onclicklistner-crashing-my-app
</details>
# 答案1
**得分**: 1
在您的`RegisterActivity`中，似乎您将适配器设置给了空的Spinner。请确保它具有正确的值，通常是一个包含字符串的ArrayAdapter。
<details>
<summary>英文:</summary>
In your RegisterActivity, seems like the Spinner you are setting the adapter to is null. Make sure it has correct value, usually its an ArrayAdapter of String.
</details>
# 答案2
**得分**: 0
错误不在LoginActivity中，在RegisterActivity中。在RegisterActivity中存在一个空指针异常，当您为微调器设置适配器时发生异常。
<details>
<summary>英文:</summary>
The error is not in LoginActivity but in RegisterActivity.There is a null pointer exception in RegisterActivity when you are setting adapter to a spinner.
</details>
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论