Question

我在网上搜索并继续尝试了5个小时，但我找不到解决问题的方法。我希望在方向改变后保持旋转器的状态。

我有两个动态创建的微调器。它们通过http请求获取项目，第一个微调器通过setOnItemSelectedListener（）方法更改第二个中的项目。我将字符串读入全局列表。

public class Global {
    public static String userName;
    public static String userType;
    public static String serverIp;
    public static int spinnerLeaguePos=0;
    public static int spinnerMatchPos=0;
    public static List<String> leagues;
    public static List<String> matches;
}

我的第一个问题是阻止活动重启。

android:configChanges="orientation|keyboardHidden"

我在清单文件中进行了此更改，以便自行处理方向更改并避免重新启动活动。

我找到了一种在互联网上处理方向更改的方法，但它对我不起作用。当我改变方向时，我得到空指针异常。

07-05 12:41:08.119: E/AndroidRuntime(26388): FATAL EXCEPTION: main
07-05 12:41:08.119: E/AndroidRuntime(26388): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MatchSelectionActivity}: java.lang.NullPointerException
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3351)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.access$700(ActivityThread.java:123)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1151)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.os.Looper.loop(Looper.java:137)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.main(ActivityThread.java:4424)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at java.lang.reflect.Method.invokeNative(Native Method)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at java.lang.reflect.Method.invoke(Method.java:511)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at dalvik.system.NativeStart.main(Native Method)
07-05 12:41:08.119: E/AndroidRuntime(26388): Caused by: java.lang.NullPointerException
07-05 12:41:08.119: E/AndroidRuntime(26388):    at com.example.MatchSelectionActivity.setLeagues(MatchSelectionActivity.java:90)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at com.example.MatchSelectionActivity.onCreate(MatchSelectionActivity.java:47)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.Activity.performCreate(Activity.java:4465)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
07-05 12:41:08.119: E/AndroidRuntime(26388):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
07-05 12:41:08.119: E/AndroidRuntime(26388):    ... 12 more

这是我到目前为止所做的。我甚至不确定我是否想要这样做。因此，任何更合适的方式都将受到赞赏。

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    spinnerLeague = (Spinner) findViewById(R.id.spinner_league);
    spinnerMatch = (Spinner) findViewById(R.id.spinner_match);

    if (savedInstanceState != null) {
        setLeagues();
        setMatches();
        spinnerLeague.setSelection(Global.spinnerLeaguePos);
        spinnerMatch.setSelection(Global.spinnerMatchPos);
    }
    else{
        Global.leagues = new ArrayList<String>();
        Global.matches = new ArrayList<String>();

        Global.leagues.add(getString(R.string.league_select));
        Global.matches.add(getString(R.string.match_select));

        GetLeagues task = new GetLeagues();
        String requestString = "http://" + Global.serverIp + ":8080/server/GetCurrentLeagues";
        task.execute(new String[] { requestString });
    }

    setContentView(R.layout.match_selection_layout);

}

public class GetLeagues extends AsyncTask<String, Void, String[]> {
    @Override
    protected String[] doInBackground(String... urls) {
        //this part works properly, and reads the leagues into Global.leagues List
    }

    @Override
    protected void onPostExecute(String[] result) {
        setLeagues();
    }
}
public class GetMatches extends AsyncTask<String, Void, String[]> {
    @Override
    protected String[] doInBackground(String... urls) {
        //this part works properly, and reads the matches into Global.matches List
    }

    @Override
    protected void onPostExecute(String[] result) {
        setMatches();
    }
}

 public void setLeagues() {

    spinnerLeague = (Spinner) findViewById(R.id.spinner_league);
    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item, Global.leagues);
    dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinnerLeague.setAdapter(dataAdapter);

    spinnerLeague.setOnItemSelectedListener(new OnItemSelectedListener() {

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

            spinnerLeague = (Spinner) findViewById(R.id.spinner_league);

            if(position!=0){
                spinnerMatch.setEnabled(true);
                Global.spinnerLeaguePos=position;

                GetMatches task = new GetMatches();
                String requestString = "http://" + Global.serverIp +":8080/server/GetCurrentMatches/"+Global.spinnerLeaguePos;
                task.execute(new String[] { requestString });
            }
            else{
                setMatches();
                spinnerMatch.setEnabled(false);
                Global.spinnerLeaguePos=position;
            }

        }

        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub

        }
    });
  }

    public void setMatches() {

    spinnerMatch = (Spinner) findViewById(R.id.spinner_match);
    ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item, Global.matches);
    dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinnerMatch.setAdapter(dataAdapter);


    spinnerMatch.setOnItemSelectedListener(new OnItemSelectedListener() {

        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            Global.spinnerMatchPos=position;
        }

        public void onNothingSelected(AdapterView<?> parent) {
            // TODO Auto-generated method stub

        }
    });
  }

Answer 1

在致电setContentView(R.layout.match_selection_layout)之前，您需要致电findViewById。否则，findViewById将返回null（因为父级View尚未充气/附加到屏幕上）。

此外，您应不使用configChanges作为绑定来修复您的活动。可以通过多种方式重新启动Activity;例如，如果用户将设备的语言设置从英语更改为西班牙语（这将导致整个Activity被销毁和创建）。始终确保方向更改正常工作...不要只是放弃它们而只是覆盖onConfigurationChanged。

使用动态微调器处理方向变化

1 个答案: