尝试使一个按钮加载另一个活动，然而点击监听器导致应用崩溃。

huangapple
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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！

  1. public class LogInActivity extends AppCompatActivity implements View.OnClickListener {
  3.     // 用户输入变量
  4.     EditText emailAddressInput;
  5.     EditText passwordInput;
  6.     Button logInButton;
  7.     Button registerButton;
  9.     @Override
  10.     protected void onCreate(Bundle savedInstanceState) {
  11.         super.onCreate(savedInstanceState);
  12.         // 将布局设置为activity_login.xml
  13.         setContentView(R.layout.activity_login);
  15.         // 获取用户输入并设置到变量中
  16.         emailAddressInput = (EditText)findViewById(R.id.emailAddressInput);
  17.         passwordInput = (EditText)findViewById(R.id.passwordInput);
  18.         logInButton = (Button)findViewById(R.id.logInButton);
  19.         registerButton = (Button)findViewById(R.id.registerButton);
  21.         logInButton.setOnClickListener(this);
  22.         registerButton.setOnClickListener(this);
  23.     }
  25.     @Override
  26.     public void onClick(View view) {
  27.         Intent registerIntent = new Intent (LogInActivity.this, RegisterActivity.class);
  29.         switch (view.getId()) {
  30.             case R.id.logInButton:
  31.                 break;
  32.             case R.id.registerButton:
  33.                 startActivity(registerIntent);
  34.                 break;
  35.         }
  36.     }
  37. }

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)。

  2. <details>
  3. <summary>英文:</summary>
  5. 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&#39;t fix it. I also tried removing &#39;implements View.OnClickListner&#39; and using it how its shown in the examples and it didn&#39;t work. Also tried changing the xml file to a LinearLayout and that didn&#39;t work either. Thanks in advance!
  7.     public class LogInActivity extends AppCompatActivity implements View.OnClickListener {
  9.     //user input variables
  10.     EditText emailAddressInput;
  11.     EditText passwordInput;
  12.     Button logInButton;
  13.     Button registerButton;
  15.     @Override
  16.     protected void onCreate(Bundle savedInstanceState) {
  17.         super.onCreate(savedInstanceState);
  18.         //set the layout to activity_login.xml
  19.         setContentView(R.layout.activity_login);
  21.         //get user inputs and set to the variables
  22.         emailAddressInput = (EditText)findViewById(R.id.emailAddressInput);
  23.         passwordInput = (EditText)findViewById(R.id.passwordInput);
  24.         logInButton = (Button)findViewById(R.id.logInButton);
  25.         registerButton = (Button)findViewById(R.id.registerButton);
  27.         logInButton.setOnClickListener(this);
  28.         registerButton.setOnClickListener(this);
  29.     }
  31.     @Override
  32.     public void onClick(View view) {
  33.         Intent registerIntent = new Intent (LogInActivity.this,RegisterActivity.class);
  35.         switch (view.getId())
  36.         {
  37.             case R.id.logInButton:
  38.                 break;
  39.             case R.id.registerButton:
  40.                 startActivity(registerIntent);
  41.                 break;
  42.         }
  43.     }
  44. }
  46. EDIT:
  47. the logcat:
  49. 2020-04-04 16:02:10.759 12718-12718/com.example.blooddonorsystem E/AndroidRuntime: FATAL EXCEPTION: main
  50.     Process: com.example.blooddonorsystem, PID: 12718
  51.     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.blooddonorsystem/com.example.blooddonorsystem.RegisterActivity}: java.lang.NullPointerException: Attempt to invoke virtual method &#39;void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)&#39; on a null object reference
  52.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
  53.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
  54.         at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
  55.         at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
  56.         at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
  57.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
  58.         at android.os.Handler.dispatchMessage(Handler.java:107)
  59.         at android.os.Looper.loop(Looper.java:214)
  60.         at android.app.ActivityThread.main(ActivityThread.java:7356)
  61.         at java.lang.reflect.Method.invoke(Native Method)
  62.         at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
  63.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
  64.      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method &#39;void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)&#39; on a null object reference
  65.         at com.example.blooddonorsystem.RegisterActivity.onCreate(RegisterActivity.java:56)
  66.         at android.app.Activity.performCreate(Activity.java:7825)
  67.         at android.app.Activity.performCreate(Activity.java:7814)
  68.         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
  69.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
  70.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)&#160;
  71.         at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)&#160;
  72.         at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)&#160;
  73.         at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)&#160;
  74.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)&#160;
  75.         at android.os.Handler.dispatchMessage(Handler.java:107)&#160;
  76.         at android.os.Looper.loop(Looper.java:214)&#160;
  77.         at android.app.ActivityThread.main(ActivityThread.java:7356)&#160;
  78.         at java.lang.reflect.Method.invoke(Native Method)&#160;
  79.         at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)&#160;
  80.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)&#160;
  82.   [1]: http://Intent%20registerIntent%20=%20new%20Intent%20(LogInActivity.this,RegisterActivity.class);
  83.   [2]: https://stackoverflow.com/questions/58830966/android-why-does-my-onclicklistner-crashing-my-app
  85. </details>
  88. # 答案1
  89. **得分**: 1
  91. 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。
  93. <details>
  94. <summary>英文:</summary>
  96. 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.
  98. </details>
  102. # 答案2
  103. **得分**: 0
  105. 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。
  107. <details>
  108. <summary>英文:</summary>
  110. 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. 
  112. </details>

huangapple
  • 本文由 发表于 2020年4月4日 22:57:59
  • 转载请务必保留本文链接：https://go.coder-hub.com/61029969.html
  • android
  • android-studio
  • java
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