I have a stupid problem but i couldnt solve it yet. I have an activity with a button in toolbar, this button open one dialog with some filter params. Here is what a i did..
Spinner spinner_categoria;
Spinner spinner_vendedor;
SeekBar seek_preco;
TextView tv_filtro;
onCreate method {
 ...
}
 onClickEvent{
     dialogFiltro();
}
    public void dialogFiltro() {
    Context context = SalesActivity.this;
    final Dialog dialog;
    dialog = new Dialog(context);
    //dialog.setContentView(R.layout.dialog_filtro);
    // dialog.setTitle("Filtro");
    //dialog.show();
    VendedorDAO auxVendedor = new VendedorDAO();
    final List<String> listVendedor = auxVendedor.getVendedorList();
    View dialogView = LayoutInflater.from(context).inflate(R.layout.dialog_filtro, null, false);
    CardView bt_cancelar = (CardView) dialogView.findViewById(R.id.cb_filtro_cancelar);
    CardView bt_aceitar = (CardView) dialogView.findViewById(R.id.cb_filtro_aceitar);
    seek_preco = (SeekBar) dialogView.findViewById(R.id.sb_preco_max);
    tv_filtro = (TextView) dialogView.findViewById(R.id.tv_filtro_preco);
    spinner_categoria = (Spinner) dialogView.findViewById(R.id.spinner_categoria);
    spinner_vendedor = (Spinner) dialogView.findViewById(R.id.spinner_vendedor);
    spinner_categoria.setAdapter(ArrayAdapter.createFromResource(
            this, R.array.categoria_array, android.R.layout.simple_spinner_item));
    spinner_vendedor.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, listVendedor));
    String oi = "oi";
    tv_filtro.setText(oi);
    dialog.setContentView(dialogView);
    dialog.show();
    seek_preco.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
        @Override
        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
            // tv_filtro.setText("R$ " + progress);
            // Log.i("RS " , String.valueOf(progress));
        }
        @Override
        public void onStartTrackingTouch(SeekBar seekBar) {
        }
        @Override
        public void onStopTrackingTouch(SeekBar seekBar) {
        }
    });
    bt_cancelar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            dialog.dismiss();
        }
    });
    bt_aceitar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            categoria = (String) spinner_categoria.getSelectedItem();
            vendedor = (Integer) spinner_vendedor.getFirstVisiblePosition();
            Log.e("id vendedor ", String.valueOf(vendedor));
            if (vendedor == 0) {
                vendedor = -1;
            }
            int precoAux = seek_preco.getProgress();
            precoMax = (float) precoAux;
        }
    });
}
I have this in dialog_filtro.xml file:
 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:cardview="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:id="@+id/card"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:layout_margin="8dp"
        android:foreground="@drawable/border_card"
        card_view:cardElevation="2dp"
        card_view:cardMaxElevation="8dp">
        <ScrollView
            android:id="@+id/scrollView2"
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_margin="16dp"
                android:orientation="vertical">
                <FrameLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal">
                    <Button
                        android:id="@+id/cb_filtro_cancelar"
                        android:layout_width="70dp"
                        android:layout_height="30dp"
                        android:background="@color/colorPrimary"
                        android:elevation="2dp"
                        android:text="X"
                        android:textColor="@android:color/white" />
                    <Button
                        android:id="@+id/cb_filtro_aceitar"
                        android:layout_width="70dp"
                        android:layout_height="30dp"
                        android:layout_gravity="end"
                        android:background="@color/colorPrimary"
                        android:elevation="2dp"
                        android:text="Aceitar"
                        android:textColor="@android:color/white" />
                </FrameLayout>
                <TextView
                    android:id="@+id/textView9"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginTop="5dp"
                    android:text="Filtrar por"
                    android:textAppearance="?android:attr/textAppearanceLarge"
                    android:textColor="@color/colorPrimary" />
                <TextView
                    android:id="@+id/tv_label_categoria"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:layout_weight="1"
                    android:gravity="center"
                    android:text="Categoria"
                    android:textAppearance="?android:attr/textAppearanceMedium" />
                <Spinner
                    android:id="@+id/spinner_categoria"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:spinnerMode="dialog" />
                <TextView
                    android:id="@+id/tv_label_vendedor"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:layout_weight="1"
                    android:gravity="center"
                    android:text="Supermercado"
                    android:textAppearance="?android:attr/textAppearanceMedium" />
                <Spinner
                    android:id="@+id/spinner_vendedor"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:spinnerMode="dialog" />
                <TextView
                    android:id="@+id/textView7"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="Preço máximo"
                    android:textAppearance="?android:attr/textAppearanceMedium" />
                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:gravity="center_vertical"
                    android:orientation="horizontal">
                    <SeekBar
                        android:id="@+id/sb_preco_max"
                        android:layout_width="0dp"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:indeterminate="false"
                        android:max="100"
                        android:progress="0" />
                    <TextView
                        android:id="@+id/tv_filtro_preco"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_marginLeft="10dp"
                        android:layout_marginRight="10dp"
                        android:text="5"
                        android:textAppearance="?android:attr/textAppearanceSmall" />
                </LinearLayout>
                <View
                    android:id="@+id/rv_shoppingcart_separator"
                    android:layout_width="match_parent"
                    android:layout_height="1dp"
                    android:layout_marginBottom="2dp"
                    android:layout_marginTop="10dp"
                    android:background="@android:color/darker_gray" />
                <TextView
                    android:id="@+id/tv_label_oerdenar"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginTop="15dp"
                    android:text="Ordenar por"
                    android:textAppearance="?android:attr/textAppearanceLarge"
                    android:textColor="@color/colorPrimary" />
                <TextView
                    android:id="@+id/textView11"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:text="Preço:"
                    android:textAppearance="?android:attr/textAppearanceMedium" />
                <RadioGroup
                    android:id="@+id/group_preco"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:layout_gravity="center"
                    android:layout_marginLeft="5dp"
                    android:layout_marginTop="10dp"
                    android:gravity="center"
                    android:orientation="horizontal">
                    <RadioButton
                        android:id="@+id/rb_preco_maior"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:checked="false"
                        android:text="Maior" />
                    <RadioButton
                        android:id="@+id/rb_preco_menor"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:checked="false"
                        android:text="Menor" />
                </RadioGroup>
                <TextView
                    android:id="@+id/tv_label_data_Validade"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginTop="10dp"
                    android:layout_weight="1"
                    android:text="Data de validade:"
                    android:textAppearance="?android:attr/textAppearanceMedium" />
                <RadioGroup
                    android:id="@+id/group_validade"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center"
                    android:layout_marginLeft="10dp"
                    android:layout_marginTop="5dp"
                    android:layout_weight="1"
                    android:gravity="center"
                    android:orientation="horizontal">
                    <RadioButton
                        android:id="@+id/rb_validade_maior"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:checked="false"
                        android:text="Maior" />
                    <RadioButton
                        android:id="@+id/rb_validade_menor"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"
                        android:checked="false"
                        android:text="Menor" />
                </RadioGroup>
                <LinearLayout
                    android:id="@+id/linear_isoffer"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:orientation="vertical">
                    <TextView
                        android:id="@+id/tv_label_ofertas"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:layout_marginTop="10dp"
                        android:layout_weight="1"
                        android:text="Apenas ofertas:"
                        android:textAppearance="?android:attr/textAppearanceMedium" />
                    <CheckBox
                        android:id="@+id/cb_offer"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:layout_marginTop="5dp"
                        android:layout_weight="1"
                        android:checked="false"
                        android:text="Selecionar apenas ofertas" />
                </LinearLayout>
            </LinearLayout>
        </ScrollView>
    </android.support.v7.widget.CardView>
</LinearLayout>
Everything works fine (spinner, cardview etc) but i always get NullPointerException because the TextView and i don't know why. Here goes my log:
FATAL EXCEPTION: main
Process: com.catafeira.catafeira, PID: 2419
Theme: themes:{default=overlay:system, iconPack:system, fontPkg:system, com.android.systemui=overlay:system, com.android.systemui.navbar=overlay:system}
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.catafeira.catafeira.SalesActivity.dialogFiltro(SalesActivity.java:281)
at com.catafeira.catafeira.SalesActivity.onOptionsItemSelected(SalesActivity.java:432)
at android.app.Activity.onMenuItemSelected(Activity.java:2914)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:403)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:189)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:100)
at android.support.v7.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:69)
at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:169)
at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:760)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:948)
at android.support.v7.widget.ActionMenuView.invokeItem(ActionMenuView.java:618)
at android.support.v7.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:139)
at android.view.View.performClick(View.java:5204)
at android.view.View$PerformClick.run(View.java:21158)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5461)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
EDIT: I know what is a NullPointerException, I already checked the previous posts on the subject, but no problem is the same as mine
 
    