Android 片段内的按钮导致应用程序崩溃

Question

我是 Android 开发的新手。 我正在尝试在我的登录片段 class 中添加一个按钮，但当前代码会导致应用程序在加载时崩溃。 想知道有没有人知道为什么

package com.hidden.hidden.ui.login;

import android.content.Context;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Button;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.ViewModelProvider;

import com.hidden.hidden.R;
import com.hidden.hidden.databinding.FragmentLoginBinding;

public class LoginFragment extends Fragment {

    private LoginViewModel homeViewModel;
    private FragmentLoginBinding binding;
    private WebView webView;

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        homeViewModel =
                new ViewModelProvider(this).get(LoginViewModel.class);


        binding = FragmentLoginBinding.inflate(inflater, container, false);
        View root = binding.getRoot();

        webView = (WebView) root.findViewById(R.id.loginWebView);
        webView.setWebViewClient(new WebViewClient());
        webView.loadUrl("hiddenurl");
        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);


        Button button = (Button) root.findViewById(R.id.buttontest);
        button.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v)
            {
                // do some toast thing
            }
        });

        return root;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }

}

随着错误

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.hidden.hidden, PID: 10145
    java.lang.ClassCastException: androidx.constraintlayout.widget.ConstraintLayout cannot be cast to android.widget.Button
        at com.hidden.hidden.ui.login.LoginFragment.onCreateView(LoginFragment.java:44)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
        at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
        at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
        at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2629)
        at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:2577)
        at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2722)
        at androidx.fragment.app.FragmentStateManager.activityCreated(FragmentStateManager.java:346)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1188)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1356)
        at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1434)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1497)
        at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2625)
        at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:2577)
        at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:247)
        at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:541)
        at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:210)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1435)
        at android.app.Activity.performStart(Activity.java:8210)
        at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3800)
        at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
        at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
        at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2289)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:246)
        at android.app.ActivityThread.main(ActivityThread.java:8462)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:596)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)

我的最终目的是在登录后从我的 webapi 以及从登录活动到 MainActivity 得到回复

谢谢

<?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:id="@+id/buttontest"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.login.LoginFragment">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button" />

    <WebView
        android:id="@+id/loginWebView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </WebView>
</androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

id buttontest分配给您的约束布局，而不是您的按钮。 只是一个简单的错字。 例外情况也非常清楚地表明了这一点。 代替

Button button = (Button) root.findViewById(R.id.buttontest);

和

Button button = (Button) root.findViewById(R.id.button);

Answer 2

尝试删除：

binding = FragmentLoginBinding.inflate(inflater, container, false);
    View root = binding.getRoot();

    webView = (WebView) root.findViewById(R.id.loginWebView);
    webView.setWebViewClient(new WebViewClient());
    webView.loadUrl("hiddenurl");
    WebSettings webSettings = webView.getSettings();
    webSettings.setJavaScriptEnabled(true);


    Button button = (Button) root.findViewById(R.id.buttontest);
    button.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            // do some toast thing
        }
    });

    return root;

从：

public View onCreateView(@NonNull LayoutInflater inflater,
                         ViewGroup container, Bundle savedInstanceState) {
    homeViewModel =
            new ViewModelProvider(this).get(LoginViewModel.class);

}

尝试添加：

 @Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    binding = FragmentLoginBinding.inflate(inflater, container, false);
    View root = binding.getRoot();

    webView = (WebView) root.findViewById(R.id.loginWebView);
    webView.setWebViewClient(new WebViewClient());
    webView.loadUrl("hiddenurl");
    WebSettings webSettings = webView.getSettings();
    webSettings.setJavaScriptEnabled(true);


    Button button = (Button) root.findViewById(R.id.buttontest);
    button.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View v)
        {
            // do some toast thing
        }
    });

    return root;
}

希望这可以帮助...

请告诉它是否工作

Answer 3

在 OnCreateView 内部：

  return inflater.inflate(R.layout.login_fragment, container, false);

尝试删除：

binding = FragmentLoginBinding.inflate(inflater, container, false);
View root = binding.getRoot();

希望这对现在有帮助...谢谢

请让我知道它是否工作。