使用動態微調器處理方向變化

Question

我已經在網上搜索並嘗試了5個小時，但找不到解決問題的方法。 方向更改后，我想保持微調器的狀態。

我有2個動態創建的微調器。 他們通過http請求獲取項目，第一個微調器通過setOnItemSelectedListener（）方法更改第二個項目。 我將字符串讀入全局列表。

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;
}

我的第一個問題是阻止活動重新啟動。

android:configChanges="orientation|keyboardHidden"

我已在清單文件中進行了此更改，以自己處理方向更改，並避免重新啟動活動。

我找到了一種方法來處理Internet上的方向更改，但對我不起作用。 更改方向時出現空指針異常。

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

到目前為止，這是我所做的。 我什至不確定我要嘗試做的事情。 因此，任何更合適的方式都可以實現。

@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

您需要先調用setContentView(R.layout.match_selection_layout)然后再調用findViewById 。 否則， findViewById將返回null （因為父View尚未被放大/附加到屏幕上）。

此外，你不應該使用configChanges作為綳帶來固定你的活動。 重新啟動Activity方法有很多。 例如，如果用戶將設備的語言設置從英語更改為西班牙語（這將導致整個Activity被銷毀和創建）。 始終確保方向更改正確起作用...不要僅僅放棄它們，而只需重寫onConfigurationChanged 。