Question

我的代码是这样的：我点击选项菜单，选择＆＃34;编辑提示率＆＃34;。然后，会出现一个弹出窗口，其中包含文本字段，取消按钮和保存按钮。我在文本字段中输入一个值，然后单击“保存”。此时我得到文本字段的空指针异常（＆＃34;字段＆＃34;，在下面的代码中）

public class MainActivity extends Activity {

    public static final String PREFS_NAME = "MyPrefs";

    // tip and tax rates
    private String tax_rate;
    private String tip_rate;

    // default tip and tax
    private String default_tax_rate = "10.0";
    private String default_tip_rate = "12.0";

    // tip and tax rate keys
    public static final String TaxRate = "tax_rate_key";
    public static final String TipRate = "tip_rate_key";

    // dialog popup
    final Context context = this;
    SharedPreferences sharedpreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Retrieve preferences
        sharedpreferences = getSharedPreferences(PREFS_NAME,
                Context.MODE_PRIVATE);

        if (sharedpreferences.contains(TaxRate)) {
            tax_rate = sharedpreferences.getString(TaxRate, "");
        } else {
            tax_rate = default_tax_rate;
        }

        if (sharedpreferences.contains(TipRate)) {
            tip_rate = sharedpreferences.getString(TipRate, "");
        } else {
            tip_rate = default_tip_rate;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }


    // This method is called once the menu is selected
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        LayoutInflater layoutInflater = LayoutInflater.from(MainActivity.this);

        switch (item.getItemId()) {

        // If edit tip rate is selected
        case R.id.item1:
            View promptView1 = layoutInflater
                    .inflate(R.layout.prompt_tip, null);

            editDialog(promptView1, TipRate, R.id.userInput_tip);
            break;

        // If edit tax rate is selected
        case R.id.item2:
            View promptView2 = layoutInflater
                    .inflate(R.layout.prompt_tax, null);
            editDialog(promptView2, TaxRate, R.id.userInput_tax);
            break;

        }
        return true;

    }

    private void editDialog(View promptView, final String key, int id) {

        AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
                context);

        // set prompts.xml to be the layout file of the alertdialog builder
        alertDialogBuilder.setView(promptView);

        // setup a dialog window
        alertDialogBuilder
                .setCancelable(false)
                .setPositiveButton("Save",
                        new DialogInterface.OnClickListener() {

                            @Override
                            public void onClick(DialogInterface dialog, int id) {
                                final EditText field = (EditText) findViewById(id);
                                if (field.getText().toString().length() == 0) {
                                    Toast.makeText(context,
                                            "enter a valid number",
                                            Toast.LENGTH_LONG).show();
                                }

                                else {
                                    // Read the value inside the textfield as a
                                    // string
                                    SharedPreferences pref = getApplicationContext()
                                            .getSharedPreferences(PREFS_NAME, 0);

                                    // Initialize the sharedPreferences editor
                                    Editor editor = pref.edit();

                                    // get value in field
                                    String value = field.getText().toString();

                                    // pair the value in text field with the key
                                    editor.putString(key, value);

                                    editor.commit();
                                }
                            }
                        })

                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                dialog.cancel();
                            }
                        });

        // create an alert dialog
        AlertDialog alertD = alertDialogBuilder.create();
        alertD.show();
    }

}

Answer 1

替换：

final EditText field = (EditText) findViewById(id)

by：

final EditText field = (EditText) promptView.findViewById(id)

因为editText包含在promptView中而不包含在Activity Layout中。

Answer 2

您得到一个例外，因为您的EditText的id不是onClick方法中的参数。变量id是单击的按钮的id。你必须使用：

 final EditText field = (EditText) findViewById(R.id.editTextId);

请参阅documentation，解释变量id是什么。

Answer 3

onclick()中的

使用此：

final EditText field = (EditText) promptView.findViewById(id)

无法在OptionsMenu的Android AlertDialog弹出窗口中保存editText值

3 个答案: