Question

我正在尝试使用“共享首选项”将列表视图中的数据保存，但是我遇到了一些错误。我有2个班级，一个是主要活动，第二个是编辑框。

MainActivity.java

public class MainActivity extends Activity 
{
    ListView listView1=null;


    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);



        final ListView listView1 = (ListView) findViewById(R.id.listView1);

         String[] items = { "List 1", "List 2", "List 3", "List 4" };



        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, items);

        listView1.setAdapter(adapter);



        listView1.setOnItemClickListener(new OnItemClickListener() 
        {

            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            {

                //String item = ((TextView)view).getText().toString();

                //Toast.makeText(getBaseContext(), item, Toast.LENGTH_LONG).show();

                //int pos = (int) listView1.getItemIdAtPosition(position);

                String value = listView1.getAdapter().getItem(position).toString();


                Intent it1 = new Intent(getApplicationContext(), editbox.class); 
                it1.putExtra("index", value );
                startActivity(it1);

            }
        });



    }

    public boolean onCreateOptionsMenu(Menu menu) 
    {

        super.onCreateOptionsMenu(menu);
        menu.add("List").setIntent(new Intent(this,MainActivity.class));
        return true;
    }

}

editbox.java

public class editbox extends Activity 
{   
    private TextView tv;
    private EditText nameText,nameText1;
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.editbox);

        //tv = (TextView) findViewById(R.id.textView1);

        //Bundle b = getIntent().getExtras();
        //int poss = b.getInt( "index");
      //  tv.setText("Position = " + poss);



        //Bundle extras=getIntent().getExtras();
        //Intent it = getIntent();
        //int myvalue = it.getIntExtra("id",0);
        //Bundle extras = it.getExtras();
        //String myvalue = extras.getString("data");

        //nameText=(EditText)findViewById(R.id.editText1);
        //nameText.setText(poss);

         Bundle b = getIntent().getExtras();
         String val = b.getString("index");
        //String val = b.getStringExtra("index");
        SharedPreferences setting = getSharedPreferences("List 1", 0);

        nameText.setText(setting.getString("List 1", "poss"));

        //nameText.setText(poss);

        //display=(EditText)findViewById(R.id.editText1);
        //display.setText(""+ myvalue);


    }

    protected void onStop() 
    {

        super.onStop();

        SharedPreferences setting = getSharedPreferences("List 1",0);
        SharedPreferences.Editor editor = setting.edit();
        editor.putString("List 1", nameText.getText().toString());

        editor.commit();

    }




    public boolean onCreateOptionsMenu(Menu menu) 
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        //getMenuInflater().inflate(R.menu.main, menu);
        super.onCreateOptionsMenu(menu);
        menu.add("List 1").setIntent(new Intent(this,MainActivity.class));

        return true;
    }
}

这些是错误

03-20 01:03:29.786: E/AndroidRuntime(1272): FATAL EXCEPTION: main
03-20 01:03:29.786: E/AndroidRuntime(1272): Process: com.example.list, PID: 1272
03-20 01:03:29.786: E/AndroidRuntime(1272): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.list/com.example.list.editbox}: java.lang.NullPointerException
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.os.Handler.dispatchMessage(Handler.java:102)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.os.Looper.loop(Looper.java:136)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread.main(ActivityThread.java:5017)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at java.lang.reflect.Method.invokeNative(Native Method)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at java.lang.reflect.Method.invoke(Method.java:515)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at dalvik.system.NativeStart.main(Native Method)
03-20 01:03:29.786: E/AndroidRuntime(1272): Caused by: java.lang.NullPointerException
03-20 01:03:29.786: E/AndroidRuntime(1272):     at com.example.list.editbox.onCreate(editbox.java:53)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.Activity.performCreate(Activity.java:5231)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-20 01:03:29.786: E/AndroidRuntime(1272):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
03-20 01:03:29.786: E/AndroidRuntime(1272):     ... 11 more

Answer 1

你有这个

nameText.setText(setting.getString("List 1", "poss"));

但是你还没有初始化nameText。其评论

//nameText=(EditText)findViewById(R.id.editText1)

Answer 2

从

中删除评论

nameText=(EditText)findViewById(R.id.editText1);

您setText至nameText未初始化(EditText)。

无法启动活动ComponentInfo {com.example.list / com.example.list.editbox}：java.lang.NullPointerException

2 个答案: