我是java的新手，我可以使用一些帮助。在以下程序中，当我旋转屏幕时，ListView消失。当我单击返回时，然后将应用程序拉回我的两个TextView并清除我的ListView。我读了一些，并从我收集它的内容，因为活动基本上重新启动这些操作。在这些情况下，我寻找一种保存信息的好方法，但我尝试过的任何工作都没有。任何帮助将不胜感激。如果我的代码很乱，我道歉，就像我说我是初学者一样。我试图使用onSavedInstanceState（）方法，但我不能让它工作。我意识到这可能是我犯的一些愚蠢的错误，但我已经在这里呆了几个小时，我无法弄清楚我做错了什么。提前谢谢。
package dev.rogueinteractive.barcodescannershoppingcartii;
import android.app.Activity;
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements OnClickListener {
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
savedInstanceState.putStringArrayList("myKey", (ArrayList<String>) productReport);
}
private static final String USER_AGENT = "Mozilla/5.0";
private static String GET_URL ;
private ArrayAdapter<String> listAdapter ;
List<String> productReport = new ArrayList<String>();
public void sendGET() throws IOException {
URL obj = new URL(GET_URL);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("GET");
con.setRequestProperty("User-Agent", USER_AGENT);
int responseCode = con.getResponseCode();
System.out.println("GET Response Code :: " + responseCode);
if (responseCode == HttpURLConnection.HTTP_OK) { // success
BufferedReader in = new BufferedReader(new InputStreamReader(
con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
// print result
fullResponse = response.toString();
String[]responseArray = fullResponse.split("\"");
String price = new String(responseArray[30]);
price = new StringBuffer(price).insert(1, " ").toString();
price = new StringBuffer(price).insert(2, "$").toString();
responseArray[30] = price;
List<String> modifiedArray = new ArrayList<String>();
modifiedArray.add(responseArray[27]);
modifiedArray.add("\n");
modifiedArray.add("\n");
modifiedArray.add(responseArray[28]);
modifiedArray.add(responseArray[29]);
modifiedArray.add(responseArray[30]);
modifiedResponse = modifiedArray.toString();
modifiedResponse= modifiedResponse.replaceAll(",", "");
modifiedResponse = modifiedResponse.replaceAll("[\\[\\]]", "");
productReport.add(modifiedResponse);
} else {
responseTXT.setText("GET request not worked");
}
}
public String modifiedResponse;
public String fullResponse;
public String scanContent;
private Button scanBtn;
private TextView formatTxt, contentTxt, responseTXT;
public ListView mainListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null) {
List<String> productReport = savedInstanceState.getStringArrayList("myKey");
if (productReport != null) {
listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, productReport);
}
}
setContentView(R.layout.activity_main);
if (android.os.Build.VERSION.SDK_INT > 9) {
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}
mainListView = (ListView) findViewById( R.id.mainListView );
scanBtn = (Button) findViewById(R.id.scan_button);
formatTxt = (TextView) findViewById(R.id.scan_format);
contentTxt = (TextView) findViewById(R.id.scan_content);
responseTXT = (TextView) findViewById(R.id.response);
scanBtn.setOnClickListener(this);
}
public void onClick(View v) {
if (v.getId() == R.id.scan_button) {
IntentIntegrator scanIntegrator = new IntentIntegrator(this);
scanIntegrator.initiateScan();
}
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent intent) {
IntentResult scanningResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, intent);
if (scanningResult.getFormatName() != null) {
this.scanContent = scanningResult.getContents();
String scanFormat = scanningResult.getFormatName();
formatTxt.setText("FORMAT: " + scanFormat);
contentTxt.setText("CONTENT: " + scanContent);
GET_URL="http://api.walmartlabs.com/v1/search?query="+scanContent+"&format=json&apiKey=5sk5b7u25b4qawku5zsm289z";
try {
sendGET();
} catch (IOException e) {
e.printStackTrace();
}
listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, productReport);
mainListView.setAdapter( listAdapter );
} else if (scanningResult==null){
Toast toast = Toast.makeText(getApplicationContext(),
"No scan data received!", Toast.LENGTH_SHORT);
toast.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.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
主要活动
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button android:id="@+id/scan_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:text="@string/scan" />
<TextView
android:id="@+id/scan_format"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textIsSelectable="true"
android:layout_centerHorizontal="true"
android:layout_below="@id/scan_button" />
<TextView
android:id="@+id/scan_content"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textIsSelectable="true"
android:layout_centerHorizontal="true"
android:layout_below="@id/scan_format" />
<ListView android:id="@+id/mainListView"
android:layout_height="fill_parent"
android:layout_width="fill_parent"
android:layout_below="@id/scan_content"/>
<TextView
android:id="@+id/response"
android:maxLines = "10000"
android:scrollbars = "vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textIsSelectable="true"
android:layout_centerHorizontal="true"
android:layout_below="@id/scan_content" />
</RelativeLayout>
行布局
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/rowTextView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:padding="10dp"
android:textSize="16sp" >
</TextView>
答案 0 :(得分：1)
我认为你错过了两件事。
首先，您没有设置mainListView适配器来接收您在onSaveInstanceState上保存的列表。请注意，如果savedInstanceState不为null，则您在onCreate方法上获取myList，但listView未接收您正在创建的新适配器。我建议在onCreate方法上添加：
...
//current code
scanBtn.setOnClickListener(this);
//New Code to be added
mainListView.setAdapter( listAdapter );
其次，如果savedInstanceState不为null，则您需要创建一个新的productReport列表以接收您在轮换之前保存的列表，但是您在其他位置使用listReport列表。您应该添加从此列表中保存的捆绑包中收到的所有商品，甚至可以重新创建产品列表。
//Current code
if (savedInstanceState != null) {
List<String> productReport = savedInstanceState.getStringArrayList("myKey");
if (productReport != null) {
listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, productReport);
}
}
//Replaced code
if (savedInstanceState != null) {
productReport = savedInstanceState.getStringArrayList("myKey");
if (productReport != null) {
listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, productReport);
}
}
另一件事：我不认为你对你获得数据的网站返回的json 100％肯定。检索数据并试图获得类似
之类的东西并不是一个好主意String price = response[30];
因为您可以轻松获得数组越界异常。 检查GSON库，也许你可以创建一个模型类来保存结果，比如
new Gson().fromJson(//your response string goes here, //your model class goes here)
最后，按下后退按钮时无法保持状态，除非您将其设置为静态或再次检索数据。