Java IllegalStateException:尝试迁移到另一个页面时无法执行android:onClick的方法？
由于大学实习的需要，我一直在开发一个应用程序，在讲师的推荐下，我从另一个学生的最后一年项目中接手了这个应用程序。我在从主菜单屏幕迁移到登录屏幕时遇到了问题 只有登录页面有问题，从应用程序的主菜单到注册页面没有任何问题，因此我假设问题可能在xml文件或LoginActivity.java中，但不知道如何解决 logcat错误如下所示：Java IllegalStateException:尝试迁移到另一个页面时无法执行android:onClick的方法？,java,android,Java,Android,由于大学实习的需要，我一直在开发一个应用程序，在讲师的推荐下，我从另一个学生的最后一年项目中接手了这个应用程序。我在从主菜单屏幕迁移到登录屏幕时遇到了问题 只有登录页面有问题，从应用程序的主菜单到注册页面没有任何问题，因此我假设问题可能在xml文件或LoginActivity.java中，但不知道如何解决 logcat错误如下所示： TAL EXCEPTION: main Process: com.finchvpn.androidcloudpark, PID: 1579 java.lan
TAL EXCEPTION: main
Process: com.finchvpn.androidcloudpark, PID: 1579
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:389)
at android.view.View.performClick(View.java:4438)
at android.view.View$PerformClick.run(View.java:18422)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:384)
at android.view.View.performClick(View.java:4438)
at android.view.View$PerformClick.run(View.java:18422)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.finchvpn.androidcloudpark.MainActivity.loginButtonClick(MainActivity.java:74)
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
android:background="@drawable/asd2">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar3"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@drawable/side_nav_bar"
app:popupTheme="@style/PopupOverlay" />
<TextView
android:id="@+id/toolbar_title"
android:layout_width="239dp"
android:layout_height="73dp"
android:layout_gravity="center"
android:layout_marginBottom="8dp"
android:text="CloudPark.my"
android:textColor="@color/md_white_1000"
android:textSize="14pt"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.11"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.014" />
<ImageButton
android:id="@+id/loginButtonPic"
android:layout_width="132dp"
android:layout_height="120dp"
android:layout_gravity="end"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_weight="1"
android:background="@null"
android:onClick="loginButtonClick"
android:scaleType="fitCenter"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.19"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.559"
app:srcCompat="@drawable/loginnew2"
tools:ignore="ContentDescription" />
<ImageButton
android:id="@+id/RegisterButtonPic"
android:layout_width="132dp"
android:layout_height="120dp"
android:layout_gravity="end"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_weight="1"
android:background="@null"
android:onClick="registerButtonClick"
android:scaleType="fitCenter"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.813"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.559"
app:srcCompat="@drawable/registernew1"
tools:ignore="ContentDescription" />
<TextView
android:id="@+id/textView2"
android:layout_width="279dp"
android:layout_height="63dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="CloudPark, the next generation parking app."
android:textColor="@color/md_white_1000"
android:textSize="10pt"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.505"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.181" />
</android.support.constraint.ConstraintLayout>
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
android:background="@drawable/asd2">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar3"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@drawable/side_nav_bar"
app:popupTheme="@style/PopupOverlay" />
<TextView
android:id="@+id/toolbar_title"
android:layout_width="307dp"
android:layout_height="91dp"
android:layout_gravity="center"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:text="Login"
android:textColor="@color/md_white_1000"
android:textSize="14pt"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.506"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<TextView
android:id="@+id/textView2"
android:layout_width="281dp"
android:layout_height="50dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Enter your credentials to access CloudPark."
android:textColor="@color/md_white_1000"
android:textSize="10pt"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.505"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.181" />
<EditText
android:id="@+id/textUsername"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Username"
android:inputType="textEmailAddress"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.352" />
<EditText
android:id="@+id/textPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Password"
android:inputType="textPassword"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.443" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:background="#0026FF"
android:onClick="loginButtonClick"
android:text="Login to CloudPark"
android:textColor="#FFFF"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.687" />
<android.support.constraint.Guideline
android:id="@+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_begin="20dp" />
</android.support.constraint.ConstraintLayout>
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
android:background="@drawable/asd2">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar3"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@drawable/side_nav_bar"
app:popupTheme="@style/PopupOverlay" />
<TextView
android:id="@+id/toolbar_title"
android:layout_width="239dp"
android:layout_height="73dp"
android:layout_gravity="center"
android:layout_marginBottom="8dp"
android:text="CloudPark.my"
android:textColor="@color/md_white_1000"
android:textSize="14pt"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.11"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.014" />
<ImageButton
android:id="@+id/loginButtonPic"
android:layout_width="132dp"
android:layout_height="120dp"
android:layout_gravity="end"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_weight="1"
android:background="@null"
android:onClick="loginButtonClick"
android:scaleType="fitCenter"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.19"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.559"
app:srcCompat="@drawable/loginnew2"
tools:ignore="ContentDescription" />
<ImageButton
android:id="@+id/RegisterButtonPic"
android:layout_width="132dp"
android:layout_height="120dp"
android:layout_gravity="end"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_weight="1"
android:background="@null"
android:onClick="registerButtonClick"
android:scaleType="fitCenter"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.813"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.559"
app:srcCompat="@drawable/registernew1"
tools:ignore="ContentDescription" />
<TextView
android:id="@+id/textView2"
android:layout_width="279dp"
android:layout_height="63dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="CloudPark, the next generation parking app."
android:textColor="@color/md_white_1000"
android:textSize="10pt"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.505"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.181" />
</android.support.constraint.ConstraintLayout>
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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"
android:background="@drawable/asd2">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar3"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@drawable/side_nav_bar"
app:popupTheme="@style/PopupOverlay" />
<TextView
android:id="@+id/toolbar_title"
android:layout_width="307dp"
android:layout_height="91dp"
android:layout_gravity="center"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:text="Login"
android:textColor="@color/md_white_1000"
android:textSize="14pt"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.506"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<TextView
android:id="@+id/textView2"
android:layout_width="281dp"
android:layout_height="50dp"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="Enter your credentials to access CloudPark."
android:textColor="@color/md_white_1000"
android:textSize="10pt"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.505"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.181" />
<EditText
android:id="@+id/textUsername"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Username"
android:inputType="textEmailAddress"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.352" />
<EditText
android:id="@+id/textPassword"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:ems="10"
android:hint="Password"
android:inputType="textPassword"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.503"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.443" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:background="#0026FF"
android:onClick="loginButtonClick"
android:text="Login to CloudPark"
android:textColor="#FFFF"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.687" />
<android.support.constraint.Guideline
android:id="@+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_begin="20dp" />
</android.support.constraint.ConstraintLayout>
public class LoginActivity extends AppCompatActivity {
private EditText textUsername;
private EditText txtPassword;
private static RestClient restClient = new RestClient();
private SharedPreferences.Editor sharedPreferencesEditor;
@SuppressLint("CommitPrefEdits")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
try {
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
Objects.requireNonNull(getSupportActionBar()).setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
} catch (Exception e) {
}
textUsername = findViewById(R.id.textUsername);
txtPassword = findViewById(R.id.textPassword);
SharedPreferences sharedPreferences = getSharedPreferences("UserInfo", 0);
sharedPreferencesEditor = sharedPreferences.edit();
textUsername.setText(sharedPreferences.getString("textUsername", ""));
txtPassword.setText(sharedPreferences.getString("txtPassword", ""));
}
public static RestClient getRestClient() {
return restClient;
}
public void loginButtonClick(View v) {
if (!textUsername.getText().toString().equals("") && !txtPassword.getText().toString().equals("")) {
apiPostLogin(Constants.ANDROID_KEY + ":" + textUsername.getText().toString() + ":" + txtPassword.getText().toString());
sharedPreferencesEditor.putString("textUsername", textUsername.getText().toString());
sharedPreferencesEditor.putString("txtPassword", txtPassword.getText().toString());
sharedPreferencesEditor.commit();
} else {
Toast.makeText(LoginActivity.this, "NULL", Toast.LENGTH_LONG).show();
}
}
private void apiPostLogin(String data) {
final ProgressDialog progress = new ProgressDialog(this);
progress.setTitle("Logging in");
progress.setMessage("Please wait ...");
progress.setCancelable(false); // disable dismiss by tapping outside of the dialog
progress.show();
Call<ResponseBody> call = getRestClient().getLoginService().postLogin(data);
call.enqueue(new Callback<ResponseBody>() {
@Override
public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
if (response.isSuccessful() && response.body() != null) {
try {
String data = response.body().string();
JSONObject jsonObject = new JSONObject(data);
Constants.uid = Integer.parseInt(jsonObject.getString("id"));
Constants.username = jsonObject.getString("username");
Constants.email = jsonObject.getString("email");
Constants.credit = jsonObject.getString("credit");
Constants.qr_code = jsonObject.getString("qr_code");
Constants.created_at = jsonObject.getString("created_at");
Constants.updated_at = jsonObject.getString("updated_at");
Toast.makeText(LoginActivity.this, "apiPostLogin onResponse <<<< \r\n\r\n" + jsonObject.toString(), Toast.LENGTH_LONG).show();
Intent returnIntent = new Intent();
setResult(Activity.RESULT_CANCELED, returnIntent);
finish();
} catch (IOException | JSONException e) {
e.printStackTrace();
}
}
progress.dismiss();
}
@Override
public void onFailure(Call<ResponseBody> call, Throwable t) {
Toast.makeText(LoginActivity.this, "Incorrect username/password, please try again." + t.getMessage(), Toast.LENGTH_LONG).show();
progress.dismiss();
}
});
}
}
我怀疑这个问题与主菜单xml和登录xml中的android:onClick=loginButtonClick的冲突有关 您不应该依赖android:onClick属性来处理视图单击。这是因为在使用android:onClick时，您无法确定处理onClick的方法是否有效。没有确切的机制来确保代码连接到视图。另一个问题是，android:onClick对Fragment不起作用。所以，我考虑使用Android：OnCalk作为坏的实践。 要解决此问题，请在视图上使用setOnClickListener。加上findViewById，您的代码将更加健壮，因为如果您为findViewById提供的id不正确，您将始终看到错误。为了使代码更加健壮并避免与id冲突，您需要为视图使用descriptive名称id。使用如下命名约定： 布局名称+\+视图的内容+\+视图类型 例如，对于登录xml，可以使用如下内容：
....
<Button
android:id="@+id/login_cloudpark_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:background="#0026FF"
android:text="Login to CloudPark"
android:textColor="#FFFF"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.687" />
<android.support.constraint.Guideline
android:id="@+id/login_begin_gdl"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_begin="20dp" />
...
通过执行上述操作，您将清晰地将xml视图与逻辑分离。请参见日志猫中的这一行，原因是：com.finchvpn.androidcloudpark.MainActivity.loginButtonClickMainActivity.java:74上的java.lang.NullPointerException。它告诉您在第74行的MainActivity中访问的某个值/变量为空，我应该将最后一段代码放在哪里？我尝试将它与findViewById一起放在LoginActivity中，但它说无法解析符号setOnClickListener.place在mBtnLogin=findViewByIdR.id.login\u cloudpark\u btn之后；