Question

我正在创建一个应该显示公交路线的应用程序我的问题是在显示路线时出现NullpointerException 使用Lyoutinflater创建动态布局我从sqlite3数据库获取数据并用光标过滤掉它我试着在5个textViews的布局中显示它我认为在TextViews中创建布局和/或显示数据是失败的。

这是我的Logcat：

java.lang.RuntimeException: Unable to start activity ComponentInfo{at.atn.android/at.atn.android.PlanAusgabeSubActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:130)
            at android.app.ActivityThread.main(ActivityThread.java:3687)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at at.atn.android.PlanAusgabeSubActivity.getRoute(PlanAusgabeSubActivity.java:111)
            at at.atn.android.PlanAusgabeSubActivity.onCreate(PlanAusgabeSubActivity.java:65)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
            at android.app.ActivityThread.access$1500(ActivityThread.java:117)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:130)
            at android.app.ActivityThread.main(ActivityThread.java:3687)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:507)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
            at dalvik.system.NativeStart.main(Native Method)

这是我的计划：

public void getRoute() {

        db = myDbHelper.getReadableDatabase();

        LayoutInflater inflater = (LayoutInflater)getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        txtAbfahrt = (TextView)findViewById(R.id.txZeit);
        txtDauer = (TextView)findViewById(R.id.txDauer);
        txtRoute = (TextView)findViewById(R.id.txUmstieg);
        txtUmstiege = (TextView)findViewById(R.id.txRoute);

        db = myDbHelper.getReadableDatabase();
        // Alle Daten der Datenbank abrufen mithilfe eines Cursors
        Cursor cursor = db.rawQuery("SELECT \tstrftime('%H:%M', f.abfahrt) AS Abfahrt,\n" +
                "\tstrftime('%H:%M', f.ankunft) AS Ankunft,\n" +
                "\tstrftime('%H:%M', strftime('%s',f.ankunft)- strftime('%s',f.abfahrt), 'unixepoch') AS Dauer,\n" +
                "\tr.name AS Route,\n" +
                "\tcount(u.fahrt_id) AS Umstiege\n" +
                "FROM \tscotty_fahrt f\n" +
                "JOIN \tscotty_haltestelle start \tON f.start_id \t= start.id\n" +
                "JOIN \tscotty_haltestelle ziel \tON f.ziel_id \t= ziel.id\n" +
                "JOIN \tscotty_route r \t\t\tON f.route_id \t= r.id\n" +
                "LEFT OUTER JOIN        scotty_umstiegsstelle u\t\t ON f.id   = u.fahrt_id\n" +
                "WHERE \tstart.name = 'Linz/Donau Hbf (Busterminal)'\n" +
                "AND \tziel.name = 'Neufelden Busterminal (Schulzentrum)'\n" +
                "GROUP BY u.fahrt_id",null);

        cursor.moveToFirst();

        while (cursor.moveToNext()){
            //in this string we get the record for each row from the column "name"
            int i =0;
            View v = inflater.inflate(R.layout.layoutausgabe,null);
            View insertPoint = findViewById(R.id.layout);

            String abfahrtszeit = cursor.getString(0);
            String dauer = cursor.getString(1);
            String route = cursor.getString(2);
            String umstiege = cursor.getString(3);

            ((ViewGroup) insertPoint).addView(v, i, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.FILL_PARENT));
            txtAbfahrt.setText(abfahrtszeit);
            txtDauer.setText(dauer);
            txtRoute.setText(route);
            txtUmstiege.setText(umstiege);
            i++;
        }

        //here we close the cursor because we do not longer need it
        //}
        cursor.close();
        myDbHelper.close();
    }

Answer 1

请使用

inflater.findViewById(R.id.txZeit);

而不是

findViewById(R.id.txZeit);

Answer 2

我认为你不会夸大你的布局。请充气：

 view = inflater.inflate(R.layout.sub_layout, null, false);

然后使用此

访问您的组件

    txtAbfahrt = (TextView)view .findViewById(R.id.txZeit);
    txtDauer = (TextView)view .findViewById(R.id.txDauer);
    txtRoute = (TextView)view .findViewById(R.id.txUmstieg);
    txtUmstiege = (TextView)view .findViewById(R.id.txRoute);

Answer 3

我认为你的textViews txtAbfahrt，txtDauer，txtRoute和txtUmstiege都包含在你的layoutausgabe中。

你需要在给layoutausgabe充气后找到它们。你需要在v变量中找到它们。

while (cursor.moveToNext()){
    //in this string we get the record for each row from the column "name"
    int i =0;
    View v = inflater.inflate(R.layout.layoutausgabe,null);
    View insertPoint = findViewById(R.id.layout);

    String abfahrtszeit = cursor.getString(0);
    String dauer = cursor.getString(1);
    String route = cursor.getString(2);
    String umstiege = cursor.getString(3);

    txtAbfahrt = (TextView)v.findViewById(R.id.txZeit);
    txtDauer = (TextView)v.findViewById(R.id.txDauer);
    txtRoute = (TextView)v.findViewById(R.id.txUmstieg);
    txtUmstiege = (TextView)v.findViewById(R.id.txRoute);

    ((ViewGroup) insertPoint).addView(v, i, new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.FILL_PARENT));
    txtAbfahrt.setText(abfahrtszeit);
    txtDauer.setText(dauer);
    txtRoute.setText(route);
    txtUmstiege.setText(umstiege);
    i++;
}

Answer 4

{
// some code here
View v = inflater.inflate(R.layout.layoutausgabe,null);
// then find view by its id


}

首先夸大布局，然后找到相关的视图

在动态创建的布局中显示数据期间的NullpointerException

4 个答案: