如何比较日期和设置按钮来设置另一个背景资源

Question

我在 String 中有两个日期，我像这样比较它们：

SimpleDateFormat formatter = new SimpleDateFormat("MMMM' 'dd', 'yyyy");

Date date1 = formatter.parse(final_date.toString());
Log.e("Taggal Selected:",date1.toString());

String str2 = "March 10, 2017";
Date date2 = formatter.parse(str2);

if (date1.compareTo(date2)<0)
{
   btn_lunch.setBackgroundResource(R.drawable.lunch_inactive);
   btn_dinner.setBackgroundResource(R.drawable.dinner_inactive);
} else if(date1.compareTo(date2)==0) {
   date.setText("Tanggal 2 sama 1");
} else {
   btn_lunch.setBackgroundResource(R.drawable.lunch_inactive);
   btn_dinner.setBackgroundResource(R.drawable.dinner_inactive);
   date.setText("Tanggal 1 lebih besar dari tanggal 2");
}

但在尝试使用 setBackgroundResource 更改按钮时它给了我错误，错误说...

java.lang.NullPointerException: 尝试调用虚方法 'void android.widget.Button.setBackgroundResource(int)' 在一个空对象上 参考

代码在尝试更改按钮或设置启用按钮时出错.. 尝试使用 textview 时代码通常可以使用... 我的错在哪里？

这是我的完整课程..

public class ProductBuyActivity extends AppCompatActivity {

    private int year;
    private int month;
    private int day;
    private int user_id;
    public String token = "",difday,diff,val;
    static TextView date;
    ImageView imgbg;
    ProgressDialog pDialog;
    public Button btn_lunch,btn_dinner;
    Context context;
    public final GlobalVar globalvar = (GlobalVar)GlobalVar.getAppContex();
    public String final_date;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.product_buy_layout);
        SharedPreferences shared = getSharedPreferences(getResources().getString(R.string.shared), MODE_PRIVATE);
        final String userdata = shared.getString("user_data", "");
        Bundle extras = getIntent().getExtras();
        try {
            JSONObject userobject = new JSONObject(userdata);
            user_id = userobject.getInt("id");
        } catch (JSONException e) {
            e.printStackTrace();
        }
        AssetManager am = this.getApplicationContext().getAssets();


        TextView login_title = (TextView)findViewById(R.id.title);

        TextView product_name = (TextView)findViewById(R.id.product_name);

        product_name.setText(globalvar.getProductName());
        TextView product_portion = (TextView)findViewById(R.id.product_portion);

        product_portion.setText(String.valueOf(globalvar.getQty())+" Portion");

        imgbg = (ImageView) findViewById(R.id.imagebg);
        String detailimg = extras.getString("ImageURL");

        int total_price = 0;
        total_price = Integer.valueOf(globalvar.getProductPrice()) * globalvar.getQty();

        if(globalvar.getFrom().equals("main")){
            total_price = Integer.valueOf(globalvar.getProductPrice()) * globalvar.getQty();
        }else{
            total_price = Integer.valueOf(globalvar.getProductPrice()) * globalvar.getQty();
        }

        TextView product_price = (TextView)findViewById(R.id.product_price);
        product_price.setTypeface(font);
        product_price.setText(HelperClass.price(String.valueOf(total_price)));
        TextView txt = (TextView)findViewById(R.id.txt1);
        txt.setTypeface(font4);
        btn_lunch = (Button) findViewById(R.id.lunch);
        btn_dinner = (Button) findViewById(R.id.dinner);
        Button btn1 = (Button)findViewById(R.id.btn1);
        btn1.setTypeface(font);
        Button btn2 = (Button)findViewById(R.id.btn2);
        btn2.setTypeface(font);

        date = (TextView)findViewById(R.id.date);
        date.setTypeface(font);
        request_validation();
        // Get current date by calender


        // Button listener to show date picker dialog


            final Calendar c = Calendar.getInstance();
            year  = c.get(Calendar.YEAR);
            month = c.get(Calendar.MONTH);
            day   = c.get(Calendar.DAY_OF_MONTH);

            // Show current date

            StringBuilder current_date = new StringBuilder()
                    // Month is 0 based, just add 1
                    .append(month + 1).append("-").append(day).append("-")
                    .append(year).append(" ");

            SimpleDateFormat dateFormat = new SimpleDateFormat("M-dd-yyyy", Locale.getDefault());
            Date mydate = null;
            try{
                mydate = dateFormat.parse(current_date.toString());
            }catch(ParseException e){
                e.printStackTrace();
            }

            SimpleDateFormat custome_date = new SimpleDateFormat("MMMM' 'dd','yyyy", Locale.getDefault());
            String final_date = custome_date.format(mydate);
            globalvar.setDate(final_date);
            date.setText(final_date);


        // Button listener to show date picker dialog

        date.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                show_date_picker();

            }

        });

        ImageView back = (ImageView)findViewById(R.id.back_button);
        back.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                go_back();
            }
        });

        globalvar.setOrderTime(0);


    }

    public void setdate(){
        GlobalVar globalvar = (GlobalVar)GlobalVar.getAppContex();
        difday = globalvar.get_diffday();
        int adddate=0;
        String logadd = String.valueOf(adddate);

        Log.e("Logadd",logadd);
        if(difday.equals("2")){
            adddate = 2;
            logadd = String.valueOf(adddate);
            Log.e("Logadd2",logadd);
        }else {
            adddate = 1;
            logadd = String.valueOf(adddate);
            Log.e("Logadd1",logadd);
        }
        final Calendar c = Calendar.getInstance();
        year  = c.get(Calendar.YEAR);
        month = c.get(Calendar.MONTH);
        day   = c.get(Calendar.DAY_OF_MONTH);

        // Show current date

        StringBuilder current_date = new StringBuilder()
                // Month is 0 based, just add 1
                .append(month + 1).append("-").append(day+adddate).append("-")
                .append(year).append(" ");

        SimpleDateFormat dateFormat = new SimpleDateFormat("M-dd-yyyy", Locale.getDefault());
        Date mydate = null;
        try{
            mydate = dateFormat.parse(current_date.toString());
        }catch(ParseException e){
            e.printStackTrace();
        }

        SimpleDateFormat custome_date = new SimpleDateFormat("MMMM' 'dd','yyyy", Locale.getDefault());
        String final_date = custome_date.format(mydate);
        globalvar.setDate(final_date);
        date.setText(final_date);

    }

    public void go_checkout(View v){

        DatabaseHandler db = new DatabaseHandler(this);

        ShoppingCartList cartlist = new ShoppingCartList();
        cartlist.setProductId(globalvar.getProductId());
        cartlist.setProductName(globalvar.getProductName());
        cartlist.setProductPrice(globalvar.getProductPrice());
        cartlist.setImage(globalvar.getImage());
        cartlist.setQty(globalvar.getQty());
        cartlist.setDate(globalvar.getDate());
        cartlist.setOrderTime(globalvar.getOrderTime());
        cartlist.setProductSellingPrice(globalvar.getProductSellingPrice());
        cartlist.setuserID(user_id);
        //db.addCart(cartlist);
        if(globalvar.getFrom().equals("main")){
            if(db.Cart_Exists(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(), user_id)){
                ShoppingCartList cart_detail = db.getCart(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(), user_id);
            }

//        if(db.Cart_Exists(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate())){
//
//            ShoppingCartList cart_detail = db.getCart(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate());
//
//            cart_detail.setQty(cart_detail.getQty() + globalvar.getQty());
//
//            db.updateChart(cart_detail);

        }else{
            db.addCart(cartlist);
        }

        if(globalvar.getFrom().equals("main")){
            if(db.Cart_Exists(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id)){

                ShoppingCartList cart_detail = db.getCart(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id);

                cart_detail.setQty(cart_detail.getQty() + globalvar.getQty());

                db.updateChart(cart_detail);

            }else{
                db.addCart(cartlist);
            }
        }
        else{
            if(db.Cart_ExistsPaket(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id)){

                ShoppingCartList cart_detail = db.getCartPaket(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id);

                cart_detail.setQty(cart_detail.getQty() + globalvar.getQty());

                db.updateChartPaket(cart_detail);

            }else{
                db.addCartPaket(cartlist);
            }
        }

        db.close();

        Toast.makeText(ProductBuyActivity.this, "Added To Shopping Cart", Toast.LENGTH_LONG).show();


        if(globalvar.getFrom().equals("main")){
            this.finish();
            Intent intent = new Intent(this, ShoppingCartActivity.class);
            startActivity(intent);
        }else{
//            this.finish();
//            Intent intent = new Intent(this, OrderPacketActivity.class);
//            startActivity(intent);
        }
    }

    public void go_addchart(View v){

        DatabaseHandler db = new DatabaseHandler(this);

        ShoppingCartList cartlist = new ShoppingCartList();
        cartlist.setProductId(globalvar.getProductId());
        cartlist.setProductName(globalvar.getProductName());
        cartlist.setProductPrice(globalvar.getProductPrice());
        cartlist.setImage(globalvar.getImage());
        cartlist.setQty(globalvar.getQty());
        cartlist.setDate(globalvar.getDate());
        cartlist.setOrderTime(globalvar.getOrderTime());
        cartlist.setProductSellingPrice(globalvar.getProductSellingPrice());
        cartlist.setuserID(user_id);
        if(globalvar.getFrom().equals("main")){


            if(db.Cart_Exists(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id)){

                ShoppingCartList cart_detail = db.getCart(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id);

                cart_detail.setQty(cart_detail.getQty() + globalvar.getQty());

                db.updateChart(cart_detail);

            }else{
                db.addCart(cartlist);
            }
        }else{
            if(db.Cart_ExistsPaket(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id)){

                ShoppingCartList cart_detail = db.getCartPaket(globalvar.getProductId(), globalvar.getOrderTime(), globalvar.getDate(),user_id);

                cart_detail.setQty(cart_detail.getQty() + globalvar.getQty());

                db.updateChartPaket(cart_detail);

            }else{
                db.addCartPaket(cartlist);
            }
        }

        db.close();

        Toast.makeText(ProductBuyActivity.this, "Added To Shopping Cart", Toast.LENGTH_LONG).show();
        if(globalvar.getFrom().equals("main")){

            this.finish();
            Intent intent = new Intent(this, MainActivity.class);
            startActivity(intent);
        }
    }

    public void selectlunch(View v){


        btn_lunch.setBackgroundResource(R.drawable.lunch_active);


        btn_dinner.setBackgroundResource(R.drawable.dinner_inactive);

        globalvar.setOrderTime(0);

    }

    public void selectdinner(View v){


        btn_lunch.setBackgroundResource(R.drawable.lunch_inactive);


        btn_dinner.setBackgroundResource(R.drawable.dinner_active);

        globalvar.setOrderTime(1);

    }

    private void show_date_picker(){
        DialogFragment newFragment = new DatePickerFragment();
        newFragment.show(getSupportFragmentManager(), "datePicker");
    }

    public static class DatePickerFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener,DatePicker.OnDateChangedListener {

        @Override
        public Dialog onCreateDialog(Bundle savedInstanceState) {
            GlobalVar globalvar = (GlobalVar)GlobalVar.getAppContex();
            String difdays = globalvar.get_diffday();
            int adddate=0;
            String logadd = String.valueOf(adddate);
            Log.e("Logadd",logadd);
            if(difdays.equals("2")){
                adddate = 2;
                logadd = String.valueOf(adddate);
                Log.e("Logadd2",logadd);
            }else {
                adddate = 1;
                logadd = String.valueOf(adddate);
                Log.e("Logadd1",logadd);
            }
            // Use the current date as the default date in the picker
            final Calendar c = Calendar.getInstance();
            int year = c.get(Calendar.YEAR);
            int month = c.get(Calendar.MONTH);
            int day = c.get(Calendar.DAY_OF_MONTH)+adddate;

            DatePickerDialog dpd = new DatePickerDialog(getActivity(), android.R.style.Theme_Holo_Light_Dialog, this, year, month, day+adddate);

            //dpd.setInverseBackgroundForced(false);
            dpd.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
            dpd.getDatePicker().setMinDate(System.currentTimeMillis() - 1000 );
            dpd.setTitle("Select Day"); // Uncomment this line to activate it

            // Create a new instance of DatePickerDialog and return it
            return dpd;
        }
        @Override
        public void onDateChanged(DatePicker datePicker, int year, int month, int dayOfMonth) {
            Log.d("Date", "Year=" + year + " Month=" + (month + 1) + " day=" + dayOfMonth);

        }
        public void onDateSet(DatePicker view, int year, int month, int day) {
            GlobalVar globalvar = (GlobalVar)GlobalVar.getAppContex();

            StringBuilder current_date = new StringBuilder()
                    // Month is 0 based, just add 1
                    .append(month + 1).append("-").append(day).append("-")
                    .append(year).append(" ");

            SimpleDateFormat dateFormat = new SimpleDateFormat("M-dd-yyyy", Locale.getDefault());
            Date mydate = null;
            try{
                mydate = dateFormat.parse(current_date.toString());
            }catch(ParseException e){
                e.printStackTrace();
            }


            SimpleDateFormat custome_date = new SimpleDateFormat("MMMM' 'dd', 'yyyy", Locale.getDefault());
            String final_date = custome_date.format(mydate);

            globalvar.setDate(final_date);
            date.setText(final_date);
            ProductBuyActivity product = new ProductBuyActivity();
            product.compareDate(final_date);
//            product.differenDate(final_date,"0");
        }


    }
    public void enabled_button(){
        btn_lunch.setBackgroundResource(R.drawable.lunch_active);
        btn_lunch.setEnabled(true);
        btn_dinner.setBackgroundResource(R.drawable.dinner_active);
        btn_dinner.setEnabled(true);
//                Toast.makeText(getBaseContext(), "date2 is Greater than my date1", Toast.LENGTH_LONG).show();

    }

    public void disabled_button(){
        btn_lunch.setBackgroundResource(R.drawable.lunch_inactive);
        btn_lunch.setEnabled(false);
        btn_dinner.setBackgroundResource(R.drawable.dinner_inactive);
        btn_dinner.setEnabled(false);
//                Toast.makeText(getBaseContext(), "date2 is Greater than my date1", Toast.LENGTH_LONG).show();

    }

    public void compareDate(String final_date) {
        try{
            Context context;
            SimpleDateFormat formatter = new SimpleDateFormat("MMMM' 'dd', 'yyyy");

            Date date1 = formatter.parse(final_date.toString());
            Log.e("Taggal Selected:",date1.toString());

            String str2 = "March 10, 2017";
            Date date2 = formatter.parse(str2);

            if (date1.compareTo(date2)<0)
            {
                System.out.print("Date2 is Greater than mydate1");
                date.setText("Tanggal 2 lebih besar dari tanggal 1");
////                btn_lunch.setBackgroundResource(R.drawable.lunch_inactive);
//                btn_lunch.setEnabled(false);
////                btn_dinner.setBackgroundResource(R.drawable.dinner_inactive);
//                btn_dinner.setEnabled(false);
                    enabled_button();
//                Toast.makeText(getBaseContext(), "date2 is Greater than my date1", Toast.LENGTH_LONG).show();
            }
            else if(date1.compareTo(date2)==0){
//                Toast.makeText(getBaseContext(), "Same Date", Toast.LENGTH_SHORT).show();
                System.out.print("Same Date");
                date.setText("Tanggal 2 sama 1");
            }
            else{
//                disabled_button();

                System.out.print("Date1 is Greater than mydate2");
                date.setText("Tanggal 1 lebih besar dari tanggal 2");
            }

        }catch (ParseException e1){
            e1.printStackTrace();
        }
    }

    public void request_token() {


        StringRequest stringRequest = new StringRequest(Request.Method.POST, getResources().getString(R.string.API) + "oauth/token",
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {

                        Log.i("respon token", response);

                        //Toast.makeText(getBaseContext(), response, Toast.LENGTH_LONG).show();Toast.makeText(getBaseContext(), response, Toast.LENGTH_LONG).show();

                        //String token = "";

                        try {

                            JSONObject return_val = new JSONObject(response);
                            token = return_val.getString("access_token");


                        } catch (JSONException e) {
                            e.printStackTrace();
                            //Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_LONG).show();
                        }

                        SharedPreferences.Editor editor = getSharedPreferences(getResources().getString(R.string.shared), MODE_PRIVATE).edit();
                        editor.putString("token", token);
                        editor.commit();

                        request_validation();

                    }
                },
                new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Toast.makeText(ProductBuyActivity.this, error.toString(), Toast.LENGTH_LONG).show();
                    }
                }) {
            @Override
            protected Map<String, String> getParams() throws AuthFailureError {
                Map<String, String> map = new HashMap<String, String>();
                map.put("grant_type", getResources().getString(R.string.grant_type));
                map.put("username", getResources().getString(R.string.username));
                map.put("password", getResources().getString(R.string.password));
                map.put("client_id", getResources().getString(R.string.client_id));
                map.put("client_secret", getResources().getString(R.string.client_secret));
                return map;
            }
        };

        RequestQueue requestQueue = Volley.newRequestQueue(this);
        stringRequest.setRetryPolicy(new DefaultRetryPolicy(15000,
                DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
                DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
        requestQueue.add(stringRequest);
    }

    private void go_back(){
        this.finish();
    }
    private void showPDialog() {
        pDialog = new ProgressDialog(ProductBuyActivity.this, R.style.MyTheme);
        //pDialog.setTitle("Loading... Please Wait");
        pDialog.setCancelable(false);
        pDialog.setProgressStyle(android.R.style.Widget_Material_ProgressBar_Large);
        pDialog.show();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

    @Override
    public void onBackPressed() {

        go_back();

    }

}

Answer 1

ProductBuyActivity product = new ProductBuyActivity();

您在没有任何意图的情况下实例化您的活动。因此，onCreate 将不会被调用。

这会使您的 compareDate 方法因尝试使用 product 的 btn_lunch 和 btn_dinner 而感到困惑，这将是未初始化的 - 因此是 null

compareDate()是公共方法，可以直接调用compareDate(final_date);可以尝试使用

ProductBuyActivity.this.compareDate(final_date);

无需实例化新的活动项目。

编辑：

如果完全重构您的代码不是一个选项，那么您需要为您的DatePickerDialog 设置一个侦听器回调。

让您的DatePickerDialog 保持静态。

不要在您的片段上实现OnDateSetListener 接口。 相反，在您的 Activity

上实现它

public static class DatePickerFragment extends DialogFragment implements DatePicker.OnDateChangedListener

public class ProductBuyActivity extends AppCompatActivity implements DatePickerDialog.OnDateSetListener

将您的 onDataSet 移动到 Activity，覆盖界面

public class ProductBuyActivity extends AppCompatActivity implements DatePickerDialog.OnDateSetListener{


    .....


    @Override
    public void onDateSet(DatePicker view, int year, int month, int day) {
        GlobalVar globalvar = (GlobalVar)GlobalVar.getAppContex();

        StringBuilder current_date = new StringBuilder()
                // Month is 0 based, just add 1
                .append(month + 1).append("-").append(day).append("-")
                .append(year).append(" ");

        SimpleDateFormat dateFormat = new SimpleDateFormat("M-dd-yyyy", Locale.getDefault());
        Date mydate = null;
        try{
            mydate = dateFormat.parse(current_date.toString());
        }catch(ParseException e){
            e.printStackTrace();
        }


        SimpleDateFormat custome_date = new SimpleDateFormat("MMMM' 'dd', 'yyyy", Locale.getDefault());
        String final_date = custome_date.format(mydate);

        globalvar.setDate(final_date);
        date.setText(final_date);
        //ProductBuyActivity product = new ProductBuyActivity();
        //product.compareDate(final_date);
        compareDate(final_date);
    }
}

编辑 2：

更改您的 DatePickerDialog 实例化：

DatePickerDialog dpd = new DatePickerDialog(getActivity(), android.R.style.Theme_Holo_Light_Dialog, (ProductBuyActivity)getActivity(), year, month, day+adddate);

Answer 2

使用下面来获得不同并实现您的目标..

public static void differenDate(String startDate, String endDate) {
    Log.d("S D", "--->   S D = " + startDate);
    Log.d("E D", "--->   E D = " + endDate);

    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd' 'HH:mm:ss.sss");
    Date sDate = null;
    Date eDate = null;
    try {
        sDate = format.parse(startDate);
        eDate = format.parse(endDate);
    } catch (ParseException e) {
        e.printStackTrace();
    }
    // final int MILLI_TO_HOUR = 1000 * 60 * 60;
    // int diff = (int) ( (eDate.getTime() - sDate.getTime()) / MILLI_TO_HOUR );
    System.out.println("DIFF = " + (eDate.getTime() - sDate.getTime()));

    int calcDiff = (int) (eDate.getTime() - sDate.getTime());

}