Question

我试图让这个代码使用android studio工作，但是模拟器中的应用程序每次运行时都会崩溃并显示“App已停止”的错误。我看了一下logcat并得到了这个错误。

logcat的：

02-11 12：39：49.826 4852-4852 / co5025.example.com.week10 E / AndroidRuntime：FATAL EXCEPTION：main 处理：co5025.example.com.week10，PID：4852 java.lang.RuntimeException：无法启动活动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） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:865）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:755）引起：java.lang.ClassCastException：android.support.v7.widget.AppCompatEditText无法强制转换为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） at java.lang.reflect.Method.invoke（Native Method）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 - 您为该按钮使用的findByViewId是EditText

这些是相同的：

editUsername =(EditText) findViewById(R.id.edit_username);
butLogin = (Button) findViewById(R.id.edit_username);

将Button更改/指向xml布局中正确的id

Answer 2

根据这个： java.lang.ClassCastException：android.support.v7.widget.AppCompatEditText无法在android.app上强制转换为android.widget.Button

您正在投射Button但是登录到您的EditText

editUsername =（EditText）findViewById（R.id.edit_username）; butLogin =（Button）findViewById（R.id.edit_username）;

在这里，您将相同的ID转换为editUsername和butLogin

java.lang.RuntimeException：无法启动活动ComponentInfo：java.lang.ClassCastException：无法强制转换为android.widget.Button

2 个答案: