android studio：2錯誤：[找不到符號變量sharedPref] && [執行任務'：app：compileDebugJavaWithJavac'執行失敗]]

Question

我在MainActivity.java遇到兩個錯誤，這可能是什么原因引起的？ 在我的舊計算機上工作正常。 試圖在eclipse ADT上運行它，就像它在舊計算機上的工作方式一樣，但是仍然給我同樣的錯誤。

錯誤1：找不到符號變量sharedPref

錯誤2：任務compileDebugJavaWithJavac的執行失敗。

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import android.view.View;
import android.view.View.OnClickListener;


    public class MainScreenActivity extends Activity{

Button btnViewProducts;
Button btnNewProduct;

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

    // Buttons
    btnViewProducts = (Button) findViewById(R.id.btnViewProducts);
    btnNewProduct = (Button) findViewById(R.id.btnCreateProduct);

    // view products click event
    btnViewProducts.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {

            // display AlertDialog with EditText to input IP address
            AlertDialog.Builder IPalert = new AlertDialog.Builder(MainScreenActivity.this);

            IPalert.setTitle("Enter IP Address");

            // Set an EditText view to get user input 
            final EditText inputIP = new EditText(MainScreenActivity.this);
            inputIP.setText("192.168.0.115/tapmanager");
            IPalert.setView(inputIP);

            IPalert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int whichButton) {

                final String ip = inputIP.getText().toString();

                if(ip.matches("")){


                    inputIP.requestFocus();
                    inputIP.setError("Please Enter Valid IP Address!");
                    Toast.makeText(MainScreenActivity.this, "Please Enter Valid IP Address", Toast.LENGTH_LONG).show();
                }else{
                    //Toast.makeText(MainActivity.this, ip, Toast.LENGTH_LONG).show();


                    SharedPreferences.Editor editOffLine = sharedPref.edit();
                    editOffLine.putBoolean("isOnline", false);
                    editOffLine.putString("ip_address", ip);
                    editOffLine.commit();

                    // Launching All products Activity
                    Intent i = new Intent(getApplicationContext(), AllProductsActivity.class);
                    startActivity(i);

                }
              }
            });

            IPalert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
              public void onClick(DialogInterface dialog, int whichButton) {
                // Canceled.
              }
            });

            IPalert.show();

            //finish();
            //break; // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


        }
    });

    // view products click event
    btnNewProduct.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            // Launching create new product activity
            Intent i = new Intent(getApplicationContext(), NewProductActivity.class);
            startActivity(i);

        }
    });
}

Answer 1

添加代碼

SharedPreferences sharedPref = getSharedPreferences(
    "MyPreferenceName", Context.MODE_PRIVATE);

之前

SharedPreferences.Editor editOffLine = sharedPref.edit();
                editOffLine.putBoolean("isOnline", false);
                editOffLine.putString("ip_address", ip);
                editOffLine.commit();

並嘗試升級成績文件中的buildToolsVersion

compileSdkVersion 23
buildToolsVersion "23.0.1"

希望對您有幫助。