android - 如何从android中的警报对话框添加字符串？

Question

我正在使用Android。现在我遇到了问题。我创建了一个程序，它将通过警报对话框从用户那里获取字符串。并将其添加到微调器中。但它在 logcat 中显示了一些异常。请任何人帮我解决这个问题。这是我的代码

**MainActivity.java**

package com.example.picker;

import java.util.ArrayList;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.text.Editable;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;

public class MainActivity extends Activity {
   Button add_button;

   Editable value;
   String inserted_value;
   AlertDialog.Builder alert;
   Spinner spinner;

   /** Items entered by the user is stored in this ArrayList variable */
   ArrayList<String> list = new ArrayList<String>();

   /** Declaring an ArrayAdapter to set items to ListView */
   ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        add_button = (Button)findViewById(R.id.addbutton);
        alert = new AlertDialog.Builder(this);
        final EditText input = new EditText(this);

         /** Getting a reference to Spinner object of the resource activity_main */
        spinner = (Spinner) findViewById(R.id.spin1);

        add_button.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                alert.setTitle("Picker");
                alert.setMessage("Enter a string...");

                // Set an EditText view to get user input 

                alert.setView(input);

                alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {
if(inserted_value !=null){

                       Log.d("GOT_TEXT",inserted_value);
                       list.add(input.getText().toString());
                     }
                    else{
                        Log.d("GOT_TEXT","inserted_value is null"); 
                     }


                    /** Setting the adapter to the ListView */
                    spinner.setAdapter(adapter);

                    /** Adding radio buttons for the spinner items */
                    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

                  }
                });

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

                alert.show();

            }
        });

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

logcat

    01-28 13:45:56.138: E/AndroidRuntime(701): FATAL EXCEPTION: main
01-28 13:45:56.138: E/AndroidRuntime(701): java.lang.NullPointerException
01-28 13:45:56.138: E/AndroidRuntime(701):  at com.example.picker.MainActivity$1$1.onClick(MainActivity.java:76)
01-28 13:45:56.138: E/AndroidRuntime(701):  at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:158)
01-28 13:45:56.138: E/AndroidRuntime(701):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-28 13:45:56.138: E/AndroidRuntime(701):  at android.os.Looper.loop(Looper.java:123)
01-28 13:45:56.138: E/AndroidRuntime(701):  at android.app.ActivityThread.main(ActivityThread.java:4627)
01-28 13:45:56.138: E/AndroidRuntime(701):  at java.lang.reflect.Method.invokeNative(Native Method)
01-28 13:45:56.138: E/AndroidRuntime(701):  at java.lang.reflect.Method.invoke(Method.java:521)
01-28 13:45:56.138: E/AndroidRuntime(701):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-28 13:45:56.138: E/AndroidRuntime(701):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-28 13:45:56.138: E/AndroidRuntime(701):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

尝试为:

if(inserted_value !=null){

   Log.d("GOT_TEXT",inserted_value); 
 }
else{
    Log.d("GOT_TEXT","inserted_value is null"); 
 }

因为当您尝试记录时inserted_value为NULL