java.lang.ClassCastException: androidx.appcompat.widget.AppCompatImageButton 不能转换为 android.widget.Button

Question

问题：我在 android 工作室中有一个 java/xml 文件。 我需要播放两个按钮； 一个用于“地图页面”，第二个用于“创建新帐户”（注册活动）。 第一个按钮工作，但第二个关闭我的应用程序。 问题是什么？

我所知道的：如果它是空的 xml 文件，则将按钮用于 go 到 xml 文件工作。

错误：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.sampleapp, PID: 8062
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sampleapp/com.example.sampleapp.SignUpActivity}: java.lang.ClassCastException: androidx.appcompat.widget.AppCompatImageButton cannot be cast to android.widget.Button
        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.ClassCastException: androidx.appcompat.widget.AppCompatImageButton cannot be cast to android.widget.Button
        at com.example.sampleapp.SignUpActivity.onCreate(SignUpActivity.java:33)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        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) 

脚本：

登录活动.java：

package com.example.sampleapp;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class LoginActivity extends AppCompatActivity {
    public EditText username;
    public EditText password;
    public TextView errorView;
    public Button login;
    public Button createNewAccount;

    public void initMapPage(){
        Intent mapPage = new Intent(LoginActivity.this, MainActivity.class);
        startActivity(mapPage);
        finish();
    }

    public void initSignUpPage(){
        Intent signUpPage = new Intent(LoginActivity.this, SignUpActivity.class);
        startActivity(signUpPage);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        username = (EditText) findViewById(R.id.UsernameBox);
        password = (EditText) findViewById(R.id.PasswordBox);
        errorView = (TextView) findViewById(R.id.errorView);
        login = (Button) findViewById(R.id.LoginButton);
        createNewAccount = (Button) findViewById(R.id.SignupButton);

        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String errorMsg = "";
                if (username.getText().toString().equals("") || password.getText().toString().equals("")) {
                    if (username.getText().toString().equals("")) {
                        errorMsg += "Username block is empty\n";
                    }
                    if (password.getText().toString().equals("")) {
                        errorMsg += "Password block is empty\n";
                    }

                    errorView.setText(errorMsg);
                }
                else {
                    initMapPage();
                }
            }
        });

        createNewAccount.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                initSignUpPage();
            }
        });
    }
}

activity_login.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=".LoginActivity">

    <TextView
        android:id="@+id/WelcomeBox"
        android:layout_width="210dp"
        android:layout_height="101dp"
        android:layout_marginTop="64dp"
        android:text="Welcome \nTo Our App!"
        android:textAlignment="center"
        android:textColor="#000000"
        android:textSize="30sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/UsernameBox"
        android:layout_width="300dp"
        android:layout_height="55dp"
        android:layout_marginTop="40dp"
        android:ems="10"
        android:hint="Username"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/WelcomeBox" />

    <EditText
        android:id="@+id/PasswordBox"
        android:layout_width="300dp"
        android:layout_height="55dp"
        android:layout_marginTop="24dp"
        android:ems="10"
        android:hint="Password"
        android:inputType="textPassword"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/UsernameBox" />

    <Button
        android:id="@+id/SignupButton"
        android:layout_width="237dp"
        android:layout_height="55dp"
        android:layout_marginTop="24dp"
        android:text="Create New Acount"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView4" />

    <Button
        android:id="@+id/LoginButton"
        android:layout_width="115dp"
        android:layout_height="63dp"
        android:layout_marginTop="12dp"
        android:text="LOGIN"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/errorView" />

    <TextView
        android:id="@+id/textView4"
        android:layout_width="60dp"
        android:layout_height="29dp"
        android:layout_marginTop="24dp"
        android:text="OR"
        android:textAlignment="center"
        android:textColor="#D3000000"
        android:textSize="24sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/LoginButton" />

    <TextView
        android:id="@+id/errorView"
        android:layout_width="209dp"
        android:layout_height="62dp"
        android:layout_marginTop="16dp"
        app:layout_constraintEnd_toEndOf="parent"
        android:textAlignment="center"
        android:textColor="#FF0000"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/PasswordBox" />

</androidx.constraintlayout.widget.ConstraintLayout>

SignUpActivity.java：

package com.example.sampleapp;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class SignUpActivity extends AppCompatActivity {

    public Button backToLogin;
    public Button SignUp;
    public EditText username;
    public EditText password;
    public EditText email;


    public void initLoginPage(){
        Intent loginPage = new Intent(SignUpActivity.this, LoginActivity.class);
        startActivity(loginPage);
        finish();
    }

    @SuppressLint("WrongViewCast")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sign_up);
        SignUp = (Button) findViewById(R.id.suButton);
        backToLogin = (Button) findViewById(R.id.back_to_login);
        username = (EditText) findViewById(R.id.UsernameBoxSignUp);
        password = (EditText) findViewById(R.id.PasswordBoxSignUp);
        email = (EditText) findViewById(R.id.EmailBox);

        backToLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                initLoginPage();
            }
        });
    }
}

activity_sign_up.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=".SignUpActivity">

    <EditText
        android:id="@+id/UsernameBoxSignUp"
        android:layout_width="300dp"
        android:layout_height="40dp"
        android:layout_marginStart="54dp"
        android:layout_marginTop="160dp"
        android:ems="10"
        android:hint="Username"
        android:inputType="textPersonName"
        android:textSize="18sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/back_to_login" />

    <EditText
        android:id="@+id/PasswordBoxSignUp"
        android:layout_width="300dp"
        android:layout_height="40dp"
        android:layout_marginStart="55dp"
        android:layout_marginTop="20dp"
        android:ems="10"
        android:hint="Password"
        android:inputType="textPassword"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/EmailBox" />

    <Button
        android:id="@+id/suButton"
        android:layout_width="170dp"
        android:layout_height="53dp"
        android:layout_marginStart="120dp"
        android:layout_marginTop="36dp"
        android:text="SignUp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/PasswordBoxSignUp" />

    <EditText
        android:id="@+id/EmailBox"
        android:layout_width="300dp"
        android:layout_height="40dp"
        android:layout_marginStart="44dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:hint="Email"
        android:inputType="textEmailAddress"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/UsernameBoxSignUp" />

    <ImageButton
        android:id="@+id/back_to_login"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="54dp"
        android:layout_marginTop="28dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="?attr/actionModeCloseDrawable" />

</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

问题是ImageButton （因此也是appcompat ）是ImageView的子类，而不是Button的子类。 如果只使用setOnClickListener类的View方法，则应该将演员表更改为该演员表，或者将其完全删除。

Answer 2

是否设置了用户名或密码文本？

Android:text="" 提示只是提示，不是实际响应。 因此，当它查找尚未设置的内容时会出错。

Answer 3

您两次调用 SignUpActivity

放置意图

Intent signUpPage = new Intent(LoginActivity.this, SignUpActivity.class);
        startActivity(signUpPage);

关于 onClick 方法

并且不要忘记在您的按钮上添加android:onClick="OnCreateAccount"