When im pressing back button my list items are get

问题:

In this activity i was trying to store data dynamically but when im pressing back button in my emulator my list items are getting deleted.....

This is my main activity...

      public class Dynamic extends Activity {

    Button bt,bt2;
    EditText et,et2;

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bt = (Button) findViewById(R.id.nameok);
        et = (EditText) findViewById(R.id.name);

        final String input = et.getText().toString();

        bt.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                if (et.getText().length() == 0) {
                    Context context = getApplicationContext();
                    CharSequence text = "Enter Your Name";
                    int duration = Toast.LENGTH_SHORT;

                    Toast toast = Toast.makeText(context, text, duration);
                    toast.show();
                } else {
                    if (et.getText().length() == 0) {
                        Context context = getApplicationContext();
                        CharSequence text = "Enter Your Number";
                        int duration = Toast.LENGTH_SHORT;

                        Toast toast = Toast.makeText(context, text, duration);
                        toast.show();
                    } else {
                    et2.setVisibility(View.VISIBLE);
                    bt2.setVisibility(View.VISIBLE);
                      bt2.setOnClickListener(new View.OnClickListener() {

                        @Override
                        public void onClick(View v) {
                            // TODO Auto-generated method stub
                            String input = et.getText().toString();
                            String input1 = et2.getText().toString();
                            Intent in = new Intent(Dynamic.this, GetList.class);
                            in.putExtra("input", input);
                            in.putExtra("input1", input1);
                            startActivity(in);


                        }
                    });

                }
                }
            }
        });
    }
    protected void onStart() {
        // TODO Auto-generated method stub
        super.onStart();

        et2 = (EditText) findViewById(R.id.number);
        bt2 = (Button) findViewById(R.id.numberok);

    }
    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;
    }

}

this is my list where im giving List:

  public class GetList extends Activity {
public void onCreate(Bundle savedInstanceState) {
    ListView lv;
    Button bt3;

    ArrayAdapter<String> a_adapter;
    ArrayList<String> x_listItems;
    ArrayList<String> y_listItems;
    super.onCreate(savedInstanceState);

    setContentView(R.layout.list);

    lv = (ListView) findViewById(R.id.listView1);
    bt3 = (Button) findViewById(R.id.nameok1);
    bt3.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent in3=new Intent(GetList.this,Dynamic.class);
            startActivity(in3);
        }
    });

    x_listItems = new ArrayList<String>();
    y_listItems = new ArrayList<String>();

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

    lv.setAdapter(a_adapter);

    Intent in = getIntent();

    String inp = in.getStringExtra("input");
    String inp1 = in.getStringExtra("input1");

    if (null != inp && inp.length() > 0) {
        x_listItems.add(inp);

        a_adapter.notifyDataSetChanged();
    }
    if (null != inp1 && inp1.length() > 0) {
        y_listItems.add(inp1);
        Log.v("num", ""+y_listItems);


    }
}

     }

回答1:

Try to declare all variables out of your oncreate method..

    public class GetList extends Activity {
     ListView lv;
        Button bt3;

        ArrayAdapter<String> a_adapter;
        ArrayList<String> x_listItems;
        ArrayList<String> y_listItems;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);

        lv = (ListView) findViewById(R.id.listView1);
        bt3 = (Button) findViewById(R.id.nameok1);
        bt3.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent in3=new Intent(GetList.this,Dynamic.class);
                startActivity(in3);
            }
        });

        x_listItems = new ArrayList<String>();
        y_listItems = new ArrayList<String>();

        Intent in = getIntent();

        String inp = in.getStringExtra("input");
        String inp1 = in.getStringExtra("input1");

        if (null != inp && inp.length() > 0) {
            x_listItems.add(inp);

            a_adapter.notifyDataSetChanged();
        }
        if (null != inp1 && inp1.length() > 0) {
            y_listItems.add(inp1);
            Log.v("num", ""+y_listItems);


        }

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

         lv.setAdapter(a_adapter);
    }


}

回答2:

if you press back button when your on your GetList Activity the value of your ArrayList will be delete because the Activity is Destroy if you want to retain the value of the ArrayList make them

ArrayList<String> x_listItems;
ArrayList<String> y_listItems;

to this

public static ArrayList<String> x_listItems;
public static ArrayList<String> y_listItems;

回答3:

I'm not sure with this:

Just remove this two lines from OnStart and paste at OnCreate. I just say this according to android lifecycle. Removing OnStart is even better

et2 = (EditText) findViewById(R.id.number);
bt2 = (Button) findViewById(R.id.numberok);

and I found some mistake in your code:

          if (et.getText().length() == 0) {
            Context context = getApplicationContext();
            CharSequence text = "Enter Your Name";
            int duration = Toast.LENGTH_SHORT;

            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
        } else {
            if (et2.getText().length() == 0) { // you noticed this as et
                Context context = getApplicationContext();
                CharSequence text = "Enter Your Number";
                int duration = Toast.LENGTH_SHORT;

                Toast toast = Toast.makeText(context, text, duration);
                toast.show();
            }