通过共享首选项更改其他活动onCheckedChange上按钮的背景颜色（？）

Question

我在MainActivity中有4个导致不同活动的按钮，默认情况下，它们被设置为具有图像背景。

我在主要活动中单击一个按钮，它将带我进入有开关的“选项”活动。 '

//creates instance of the button and redirects to appropriate activity/class on button click
        //options
        Button options = findViewById(R.id.options);
        options.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intentOptions = new Intent(MainActivity.this, Options.class);
                startActivity(intentOptions);
            }
        });

'

选中该开关后，我希望“选项”背景（供用户反馈）更改为一种颜色，因此MainActivity中有4个按钮（我不想启动MainActivity）。

但是，显然我收到了空对象引用错误，因为我尝试在另一个活动中更改smth。

我在这里阅读了很多类似的主题，并且我了解到我应该使用共享首选项存储smth（什么？），这将允许我更改另一个活动中按钮的背景，然后将其（如何？）传递给Options并将其传递返回（？）从开关上的选项中检查（???）。

我是Java和android的新手，我无法掌握如何解决问题。

选项类中的代码：

`
@Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.options);
        //on toggle switch changes options background and activities buttons background in main layout to plain color
            final Switch optionPlainColored = findViewById(R.id.switch1);
            optionPlainColored.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                    ImageView background = findViewById(R.id.background);
                    Button attractionsAndArchitecture = findViewById(R.id.attractions_and_architecture);
                    Button barsAndRestaurants = findViewById(R.id.bars_and_restaurants);
                    Button sportAndRecreations = findViewById(R.id.sports_and_recreation);
                    Button nightlifeAndCulture = findViewById(R.id.culture_and_nightlife);
                    //on switch toggle changes background of options activity and 4 buttons in main activity
                    if(optionPlainColored.isChecked()){
                        background.setImageResource(R.drawable.setoptionsbackgroundcolor2);
                        attractionsAndArchitecture.setBackgroundColor(getResources().getColor(R.color.attractionsPlainColor));
                        barsAndRestaurants.setBackgroundColor(getResources().getColor(R.color.barsPlainColor));
                        sportAndRecreations.setBackgroundColor(getResources().getColor(R.color.sportsPlainColor));
                       nightlifeAndCulture.setBackgroundColor(getResources().getColor(R.color.culturePlainColor));
                    }else{
                        //when unchecked reverses the change
                       background.setImageResource(R.drawable.optionsbackground);
                       attractionsAndArchitecture.setBackground(getResources().getDrawable(R.drawable.placestovisitbackground));
                       barsAndRestaurants.setBackground(getResources().getDrawable(R.drawable.barandrestuarantsbackground));
                       sportAndRecreations.setBackground(getResources().getDrawable(R.drawable.sportandrecreationbackground));
                       nightlifeAndCulture.setBackground(getResources().getDrawable(R.drawable.nightlifeandculturebackground));

                    }

                }
            });
            //displays toast message about the switch
            Toast.makeText(getApplicationContext(), "Toggling the switch will change background color of the Options and Homescreen to plain colored one",
                    Toast.LENGTH_LONG).show();
    }

`

我正在更改背景的行上的空对象引用。

MainActivity上的XML：

'<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/backgroundinfoadditional"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/attractions_and_architecture"
        style="@style/buttonToActivity"
        android:layout_width="205dp"
        android:layout_height="285dp"
        android:layout_marginBottom="8dp"
        android:background="@drawable/placestovisitbackground"
        android:text="@string/attractions_and_architecture"
        app:layout_constraintBottom_toTopOf="@+id/title"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/bars_and_restaurants"
        style="@style/buttonToActivity"
        android:layout_width="208dp"
        android:layout_height="280dp"
        android:layout_marginBottom="8dp"
        android:background="@drawable/barandrestuarantsbackground"
        android:text="@string/bars_and_restaurants"
        app:layout_constraintBottom_toTopOf="@+id/title"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

    <Button
        android:id="@+id/sports_and_recreation"
        style="@style/buttonToActivity"
        android:layout_width="208dp"
        android:layout_height="284dp"
        android:background="@drawable/sportandrecreationbackground"
        android:text="@string/sports_and_recreation"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/title"
        app:layout_constraintVertical_bias="0.0" />

    <Button
        android:id="@+id/culture_and_nightlife"
        style="@style/buttonToActivity"
        android:layout_width="204dp"
        android:layout_height="282dp"
        android:background="@drawable/nightlifeandculturebackground"
        android:text="@string/culture_and_nightlife"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/title" />


    <Button
        android:id="@+id/options"
        style="@style/options"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.024"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0" />

    <Button
        android:id="@+id/info"
        style="@style/info"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.952"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/title"
        app:layout_constraintVertical_bias="1.0" />

    <TextView
        android:id="@+id/title"
        style="@style/title"
        android:layout_width="match_parent"
        android:layout_height="39dp"
        android:text="@string/moscow_concise_guide"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

'

Answer 1

使用处理程序将消息传递给mainactivity。 喜欢

if (MainActivity.xhandler != null) {
        Message msg = new Message();
        msg.what = message;
        msg.obj = data1;
        MainActivity.xhandler.sendMessage(msg);
}

在MainActivity中定义处理程序。

Handler xhandler=new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            return false;
        }
    });

Answer 2

得到了一个从其他来源获得的答案，将其发布在此处（不使用共享的偏好）：“我认为使用单独的Activity作为选项的替代方法是使用DialogFragment。这将允许在其中显示浮动窗口在MainActivity布局的顶部，然后在其中加载选项布局，包括Switch。

按照这个想法，您需要为这些选项创建一个DialogFragment，而不是新的Activity。

然后，假设您在“活动”中有一个按钮，并且想要更改颜色。 您可以像这样参考按钮

getActivity（）。findViewById（R.id.button）就是这样：slight_smile：

这样一来，您就可以访问“活动”中的任何视图，更改背景颜色，分配其他图像或任何所需的内容，而不必处理首选项或访问其他“活动”。

OptionsDialogFragment类：

import android.app.DialogFragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CompoundButton;
import android.widget.Switch;

public class OptionsDialogFragment extends DialogFragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        // Here we inflate the layout to use with the options dialog
        View dialogView = inflater.inflate(R.layout.options, container, false);

        final Switch optionPlainColored = dialogView.findViewById(R.id.switch1);

        optionPlainColored.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean b) {

                if(optionPlainColored.isChecked()){
                    // we use getActivity() to refer to the views in the Activity layout.
                    getActivity().findViewById(R.id.attractions_and_architecture).setBackgroundColor(getResources().getColor(R.color.attractionsPlainColor));
                    getActivity().findViewById(R.id.bars_and_restaurants).setBackgroundColor(getResources().getColor(R.color.barsPlainColor));
                    getActivity().findViewById(R.id.sports_and_recreation).setBackgroundColor(getResources().getColor(R.color.sportsPlainColor));
                    getActivity().findViewById(R.id.culture_and_nightlife).setBackgroundColor(getResources().getColor(R.color.culturePlainColor));
                } else {
                    getActivity().findViewById(R.id.attractions_and_architecture).setBackground(getResources().getDrawable(R.drawable.backgroundattractionsandarchitecture));
                    getActivity().findViewById(R.id.bars_and_restaurants).setBackground(getResources().getDrawable(R.drawable.backgroundbarsandrestaurants));
                    getActivity().findViewById(R.id.sports_and_recreation).setBackground(getResources().getDrawable(R.drawable.backgroundsportsandrecreation));
                    getActivity().findViewById(R.id.culture_and_nightlife).setBackground(getResources().getDrawable(R.drawable.backgroundnightlifeandculture));
                }
            }
        });

        return dialogView;
    }
}'

在MainActivity中：

'        Button options = findViewById(R.id.options);
        options.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                OptionsDialogFragment dialogFrag = new OptionsDialogFragment();
                FragmentManager fm = getFragmentManager();
                dialogFrag.show(fm, "Options");

            }
        });'