Question

我是Android Studio的初学者。我正在使用Windows。我的主要活动出错了。错误：在android中非法启动表达式。请帮我解决这个问题。提前谢谢。

守则

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button Expense=(Button)findViewById(R.id.Expense);
        Button Income=(Button) findViewById(R.id.Income);

        Expense.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent intent = new Intent(MainActivity.this, Addpanel.class);
                startActivity(intent);

            }

        });

        Income.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                Intent intent1 = new Intent(MainActivity.this, Addincome.class);
                startActivity(intent1);

            }

        });

        public class MainActivity extends ActionBarActivity {
            DatabaseHelper myDb;
            EditText editproduct,editamount;
            Button btnsave;
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_addpanel);
                myDb = new DatabaseHelper(this);
                editproduct = (EditText)findViewById(R.id.product);
                editamount = (EditText)findViewById(R.id.amount);
                btnsave = (Button)findViewById(R.id.save);
                save();
            }
            public  void save() {
                btnsave.setOnClickListener(
                        new View.OnClickListener() {
                            @Override
                            public void onClick(View v) {
                                boolean isInserted = myDb.insertData(editproduct.getText().toString(),
                                        editamount.getText().toString()
                                );
                                if(isInserted == true)
                                    Toast.makeText(MainActivity.this,"Data Inserted",Toast.LENGTH_LONG).show();
                                else
                                    Toast.makeText(MainActivity.this,"Data not     Inserted",Toast.LENGTH_LONG).show();
                            }
                        }
                );
            }
            public void showMessage(String title,String Message){
                AlertDialog.Builder builder = new AlertDialog.Builder(this);
                builder.setCancelable(true);
                builder.setTitle(title);
                builder.setMessage(Message);
                builder.show();
            }
            @Override
            public boolean onCreateOptionsMenu(Menu menu) {
                getMenuInflater().inflate(R.menu.menu_main, menu);
                return true;
            }
            @Override
            public boolean onOptionsItemSelected(MenuItem item) {
                int id = item.getItemId();

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

                return super.onOptionsItemSelected(item);
            }
        }
    }
}

Answer 1

您已在代码中创建了两个MainActivity，因此您会收到非法启动表达式的错误。您必须在单一类Mainactivity中编写代码。

Answer 2

您有两个MainActivity，可能导致错误。试着摆脱其中一个。

Answer 3

在一个类中有两个活动需要为两个MainActivity创建两个单独的类。

主要活动上的错误消息

3 个答案: