java - java.lang.RuntimeException:无法启动 Activity ComponentInfo:java.lang.ClassCastException:无法转换为android.widget.Button

Question

我试图使用android studio来使此代码正常工作，但是每次运行模拟器时，模拟器中的应用程序都会崩溃，并显示错误“应用程序已停止”。我查看了logcat并收到此错误。

Logcat:

02-11 12:39:49.826 4852-4852 / co5025.example.com.week10 E / AndroidRuntime:FATAL EXCEPTION:main
流程:co5025.example.com.week10，PID:4852
java.lang.RuntimeException:无法启动 Activity ComponentInfo {co5025.example.com.week10 / co5025.example.com.week10.MainActivity}:java.lang.ClassCastException:android.support.v7.widget.AppCompatEditText无法转换为android.widget.Button
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
在android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1460)
在android.os.Handler.dispatchMessage(Handler.java:102)
在android.os.Looper.loop(Looper.java:154)
在android.app.ActivityThread.main(ActivityThread.java:6077)
在java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:865)
在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
造成原因:java.lang.ClassCastException:android.support.v7.widget.AppCompatEditText无法转换为android.widget.Button
在co5025.example.com.week10.MainActivity.onCreate(MainActivity.java:42)
在android.app.Activity.performCreate(Activity.java:6664)
在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
在android.app.ActivityThread.-wrap12(ActivityThread.java)
在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1460)
在android.os.Handler.dispatchMessage(Handler.java:102)
在android.os.Looper.loop(Looper.java:154)
在android.app.ActivityThread.main(ActivityThread.java:6077)
在java.lang.reflect.Method.invoke(本机方法)
在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:865)
在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

MainActivity.java

package co5025.example.com.week10;

            import android.app.FragmentManager;
            import android.content.Intent;
            import android.os.Bundle;
            import android.support.design.widget.FloatingActionButton;
            import android.support.design.widget.Snackbar;
            import android.support.v7.app.AppCompatActivity;
            import android.support.v7.widget.Toolbar;
            import android.view.Menu;
            import android.view.MenuItem;
            import android.view.View;
            import android.widget.Button;
            import android.widget.EditText;
            import android.widget.TextView;
            import android.support.v4.app.FragmentManager.BackStackEntry;

            public class MainActivity extends AppCompatActivity implements View.OnClickListener {
                EditText editUsername;
                EditText editPassword;
                TextView errorMessage;
                Button butLogin;
                private FragmentManager.BackStackEntry v;

                @Override
                protected void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);
                    setContentView(R.layout.activity_main);
                    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
                    setSupportActionBar(toolbar);

                    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
                    fab.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                                    .setAction("Action", null).show();
                        }
                    });
                    editPassword    =   (EditText)  findViewById(R.id.edit_password);
                    editUsername    =   (EditText)  findViewById(R.id.edit_username);
                    butLogin    =   (Button) findViewById(R.id.edit_username);
                    butLogin.setOnClickListener(this);

                    if (getIntent().getBooleanExtra("EXIT", false)) finish();
                }

                @Override
                public void onClick(View view) {
                    if  (checkPassword())   {
                        Intent  i;
                        switch  (v.getId()) {
                            case    R.id.but_login:
                                i   =   new Intent(this,    GameActivity.class);
                                startActivity(i);
                                break;
                        }
                    }else{
                        errorMessage    =   (TextView)  findViewById(R.id.error_message);
                        errorMessage.setText("Error: Incorrect Password/Username. Try again!");
                    }
                }

                @Override
                public boolean onCreateOptionsMenu(Menu menu) {
                    // Inflate the menu; this adds items to the action bar if it is present.
                    getMenuInflater().inflate(R.menu.menu_main, menu);
                    return true;
                }

                @Override
                public boolean onOptionsItemSelected(MenuItem item) {
                    // Handle action bar item clicks here. The action bar will
                    // automatically handle clicks on the Home/Up button, so long
                    // as you specify a parent activity in AndroidManifest.xml.
                    int id = item.getItemId();

                    //noinspection SimplifiableIfStatement
                    if (id == R.id.action_settings) {
                        return true;
                    }

                    return super.onOptionsItemSelected(item);
                }

                public  boolean checkPassword(){
                    if  (editUsername.getText().toString().equals("test")   &&
                            (editPassword.getText().toString().equals("1234")))
                        return  true;
                    else
                        return  false;
                }
            }

Answer 1

Stacktrace告诉您出了什么问题:AppCompatEditText cannot be cast to android.widget.Button-您用于按钮的findByViewId用于EditText
这些都是一样的:
editUsername =(EditText) findViewById(R.id.edit_username);butLogin = (Button) findViewById(R.id.edit_username);

从您的xml布局中将Button更改/指向正确的id