java - 实例化 Activity 时出错

Question

我已经解决了这个问题，我检查了我的 list 文件，它告诉我我的 Activity 不再具体，我错误地将类更改为抽象，将其从抽象改回修复了错误

我在我的应用程序中添加了一个界面，这样我就可以根据 ListView 中的按钮单击来编辑文本编辑，在我添加到此界面之前，该应用程序运行良好，现在当我尝试运行该应用程序时出现错误。我搜索了论坛，但找到了解决我的问题的方法，希望有人能提供帮助!

这是我的主要 Activity

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.os.Handler;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import com.pinchtapzoom.R;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.SQLException;

public abstract class MyActivity extends Activity implements MyAdapterInterface{

    private CustomCursorAdapter customAdapter;
    public ListView list1;

    com.example.rory.dbtest.DBAdapter db = new com.example.rory.dbtest.DBAdapter(this);

    //public EditText TotalCost;
    //public EditText TotalLitres;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        list1 = (ListView)findViewById(R.id.data_list);
        db.open();


        final MyAdapterInterface ad = new MyAdapterInterface() {
            @Override
            public void updateEditText(int value) {
                EditText myEditText = (EditText)findViewById(R.id.edit1);
                myEditText.setText(value);
            }
        };


        Button addBtn = (Button)findViewById(R.id.add);
        addBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent i = new Intent(MyActivity.this, addassignment.class);
                startActivity(i);
            }
        });

        Button deleteBtn = (Button)findViewById(R.id.delete);
        deleteBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent i = new Intent(MyActivity.this, Delete.class);
                startActivity(i);
            }
        });

        Button updateBtn = (Button)findViewById(R.id.update);
        updateBtn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent i = new Intent(MyActivity.this, Update.class);
                startActivity(i);
            }
        });


        try {
            String destPath = "/data/data/" + getPackageName() + "/databases/AssignmentDB";
            File f = new File(destPath);
            if (!f.exists()) {
                CopyDB( getBaseContext().getAssets().open("mydb"),
                        new FileOutputStream(destPath));
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }


        new Handler().post(new Runnable() {
            @Override
            public void run() {
                //Log.d("test", "customadapter is " + customAdapter.toString());
                //Log.d("test", "databaseHelper is " + databaseHelper.toString());
                customAdapter = new CustomCursorAdapter(MyActivity.this, db.getAllRecords(), ad);
                list1.setAdapter(customAdapter);
            }
        });




/*        @Override
        public void updateEditText(String value) {
            EditText myEditText = (EditText)findViewById(R.id.edit1);
            myEditText.setText(value);
        }*/


    }

    private class DBAdapter extends BaseAdapter {
        private LayoutInflater mInflater;
        //private ArrayList<>

        @Override
        public int getCount() {

            return 0;
        }

        @Override
        public Object getItem(int arg0) {

            return null;
        }

        @Override
        public long getItemId(int arg0) {

            return 0;
        }

        @Override
        public View getView(int arg0, View arg1, ViewGroup arg2) {

            return null;
        }

    }

    public void CopyDB(InputStream inputStream, OutputStream outputStream)
            throws IOException {
        //---copy 1K bytes at a time---
        byte[] buffer = new byte[1024];
        int length;
        while ((length = inputStream.read(buffer)) > 0) {
            outputStream.write(buffer, 0, length);
        }
        inputStream.close();
        outputStream.close();
    }    
}

这是我的适配器类

import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.CursorAdapter;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import com.pinchtapzoom.R;


public class CustomCursorAdapter extends CursorAdapter{

    public int counter = 0;
    private MyAdapterInterface mMyInterface;

    public CustomCursorAdapter(Context context, Cursor c, MyAdapterInterface myInterface) {

        super(context, c);
        this.context = context;
        this.mMyInterface = myInterface;
    }
    Context context;


    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        // when the view will be created for first time,
        // we need to tell the adapters, how each item will look
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View retView = inflater.inflate(R.layout.row, parent, false);

        return retView;
    }

    public void bindView(View view, Context context, Cursor cursor) {
        // here we are setting our data
        // that means, take the data from the cursor and put it in views
        TextView textViewPersonName = (TextView) view.findViewById(R.id.item1);
        textViewPersonName.setText(cursor.getString(cursor.getColumnIndex(cursor.getColumnName(1))));

        final EditText edit1 = (EditText) view.findViewById(R.id.runningTotal);

        Button plusButton = (Button) view.findViewById(R.id.plusButton);
        plusButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                counter++;
                edit1.setText(Integer.toString(counter));
                mMyInterface.updateEditText(counter);
            }
        });

        final Button minusButton = (Button) view.findViewById(R.id.minusButton);
        minusButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                counter--;
                edit1.setText(Integer.toString(counter));
                mMyInterface.updateEditText(counter);
            }
        });
    }
}

这是我的界面

public interface MyAdapterInterface {

    public void updateEditText(int value);
}

这是我收到的 logcat 错误

    Process: com.example.rory.dbtest, PID: 10950
    java.lang.RuntimeException: Unable to instantiate activity      ComponentInfo{com.example.rory.dbtest/com.example.rory.dbtest.MyActivity}:   java.lang.InstantiationException: can't instantiate class com.example.rory.dbtest.MyActivity
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5001)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.InstantiationException: can't instantiate class     com.example.rory.dbtest.MyActivity
        at java.lang.Class.newInstanceImpl(Native Method)
        at java.lang.Class.newInstance(Class.java:1208)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)

            

Answer 1

final MyAdapterInterface ad = new MyAdapterInterface() {
            @Override
            public void updateEditText(int value) {
                EditText myEditText = (EditText)findViewById(R.id.edit1);
                myEditText.setText(value);
            }
        };

不应该发生在 onCreate() 方法内部，而应该发生在类的其他地方，作为普通方法。应该这样写:

public void updateEditText(int value) {
      EditText myEditText = (EditText)findViewById(R.id.edit1);
      myEditText.setText(value);
}