重定向按钮 - Android Studio 登录活动

Question

遇到问题，我编写了登录管理器应用程序，但最后我遇到了应用程序"不幸已停止"的问题

也许你可以帮助这有什么问题？

package com.example.micha.notes;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity  {
    Button b1,b2;
    EditText ed1,ed2;
    TextView tx1;
    int counter = 3;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        b1 = (Button)findViewById(R.id.button);
        ed1 = (EditText)findViewById(R.id.editText);
        ed2 = (EditText)findViewById(R.id.editText2);
        b2 = (Button)findViewById(R.id.button2);
        tx1 = (TextView)findViewById(R.id.textView3);
        tx1.setVisibility(View.GONE);
        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(ed1.getText().toString().equals("a") &&
                        ed2.getText().toString().equals("a")) {
                   // Toast.makeText(getApplicationContext(), "Redirecting...", Toast.LENGTH_SHORT).show();
                    Intent toy = new Intent(MainActivity.this, ListActivity.class);
                    startActivity(toy);
                }else{
                    Toast.makeText(getApplicationContext(), "Wrong Credentials",Toast.LENGTH_SHORT).show();
                            tx1.setVisibility(View.VISIBLE);
                    tx1.setBackgroundColor(Color.RED);
                    counter--;
                    tx1.setText(Integer.toString(counter));
                    if (counter == 0) {
                        b1.setEnabled(false);
                    }
                }
            }
        });
        b2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
    }
}

我认为错误在这里的某个地方，但不知道该怎么办:(

public void onClick(View v) {
                if(ed1.getText().toString().equals("a") &&
                        ed2.getText().toString().equals("a")) {
                   // Toast.makeText(getApplicationContext(), "Redirecting...", Toast.LENGTH_SHORT).show();
                    Intent toy = new Intent(MainActivity.this, ListActivity.class);
                    startActivity(toy);
                }else{

Answer 1

您是否向清单添加了活动？

Intent toy = new Intent(MainActivity.this, ListActivity.class);

列表活动？

<activity
        android:name=".ListActivity"
        android:configChanges="keyboardHidden|orientation|screenSize"/>