java - 使用 AlertDialog 中的上下文函数从 MainActivity 获取方法时出现问题

Question

我的 MainActivity() 中有这段代码，用于计算总记录并读取它。

public void countRecords() {
    int recordCount = new TableControllerStudent(this).count();

    TextView textViewRecordCount = (TextView) findViewById(R.id.textViewRecordCount);
    textViewRecordCount.setText(recordCount + " records found.");

}

public void readRecords() {

    LinearLayout linearLayoutRecords = (LinearLayout) findViewById(R.id.linearLayoutRecords);
    linearLayoutRecords.removeAllViews();

    List<ObjectStudent> students = new TableControllerStudent(this).read();

    if (students.size() > 0) {

        for (ObjectStudent obj : students) {

            int id = obj.id;
            String studentFirstname = obj.firstname;
            String studentEmail = obj.email;

            String textViewContents = studentFirstname + " - " + studentEmail;

            TextView textViewStudentItem= new TextView(this);
            textViewStudentItem.setPadding(0, 10, 0, 10);
            textViewStudentItem.setText(textViewContents);
            textViewStudentItem.setTag(Integer.toString(id));

            linearLayoutRecords.addView(textViewStudentItem);
        }

    }

    else {

        TextView locationItem = new TextView(this);
        locationItem.setPadding(8, 8, 8, 8);
        locationItem.setText("No records yet.");

        linearLayoutRecords.addView(locationItem);
    }
}

并且在 Activity OnListenerCreateStudent 中，此代码不起作用并出现错误。

    package com.example.coba_crud_db_1;

import android.content.Context;
import android.content.DialogInterface;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

import androidx.appcompat.app.AlertDialog;

public class OnClickListenerCreateStudent implements View.OnClickListener {
    @Override
    public void onClick(View view) {
        final Context context = view.getRootView().getContext();

        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        final View formElementsView = inflater.inflate(R.layout.student_input_form, null, false);

        final EditText editTextStudentFirstname = (EditText) formElementsView.findViewById(R.id.editTextStudentFirstname);
        final EditText editTextStudentEmail = (EditText) formElementsView.findViewById(R.id.editTextStudentEmail);

        new AlertDialog.Builder(context)
                .setView(formElementsView)
                .setTitle("Create Student")
                .setPositiveButton("Add",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                String studentFirstname = editTextStudentFirstname.getText().toString();
                                String studentEmail = editTextStudentEmail.getText().toString();

                                ObjectStudent objectStudent = new ObjectStudent();
                                objectStudent.firstname= studentFirstname;
                                objectStudent.email= studentEmail;

                                boolean createSuccessful = new TableControllerStudent(context).create(objectStudent);

                                if(createSuccessful){
                                    Toast.makeText(context, "Student information was saved.", Toast.LENGTH_SHORT).show();

                                }else{
                                    Toast.makeText(context, "Unable to save student information.", Toast.LENGTH_SHORT).show();
                                }
                                ((MainActivity)context).countRecords();
                                dialog.cancel();
                            }
                        }).show();
    }
}

错误日志:

2020-01-31 11:39:18.357 12917-12917/com.example.coba_crud_db_1 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.coba_crud_db_1, PID: 12917
java.lang.ClassCastException: com.android.internal.policy.DecorContext cannot be cast to com.example.coba_crud_db_1.MainActivity
    at com.example.coba_crud_db_1.OnClickListenerCreateStudent$1.onClick(OnClickListenerCreateStudent.java:46)
    at androidx.appcompat.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:201)
    at android.app.ActivityThread.main(ActivityThread.java:6810)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
    2020-01-31 11:39:18.417 12917-12917/com.example.coba_crud_db_1 I/Process: Sending signal. PID: 
    12917 SIG: 9

问题出在 ((MainActivity)context).countRecords();和 ((MainActivity)context).readRecords();我猜。我尝试了不同的代码，但它不起作用，如果我添加新记录，它就会强制关闭。

Answer 1

您能否分享您显示警报对话框的代码？此外，将上下文转换到 Activity 中也不是一个好的做法。当您拥有大型代码库并且多次使用相同的对话框时，这将是一个问题。最好创建一个接口(interface)并传递给alertdialog，并在您的 Activity/fragment 中使用接口(interface)的回调。