空对象引用上的 Sharedpreferences Context()

Question

我是共享首选项的新手。我遵循了 youtube 上的教程，他的代码运行良好。但我的代码没有。我正在做的是为 Sharedpreferences 创建一个 class。然后另一个 class 在其上创建 Acions。然后我的第三个 class 访问这些操作并使它们在适配器中工作。这是我的代码，以及我遇到的错误。

PrefConfig

object PrefConfig {
private const val MY_PREFERENCE_NAME = "com.moataz.afternoonhadeeth.utils.helper"
private const val PREF_TOTAL_KEY = "pref_total_key"

fun saveTotalInPref(context: Context, total: Int) {
    val pref = context.getSharedPreferences(MY_PREFERENCE_NAME, Context.MODE_PRIVATE)
    val editor = pref.edit()
    editor.putInt(PREF_TOTAL_KEY, total)
    editor.apply()
}

fun loadTotalFromPref(context: Context): Int {
    val pref = context.getSharedPreferences(MY_PREFERENCE_NAME, Context.MODE_PRIVATE)
    return pref.getInt(PREF_TOTAL_KEY, 0)
    }
}

CounterActions

class CounterActions : AppCompatActivity() {

var counter = PrefConfig.loadTotalFromPref(this)

fun displayCounter(buttonCounter: Button) {
    buttonCounter.text = counter.toString()
}

fun addCounter(buttonCounter: Button) {
    counter++
    PrefConfig.saveTotalInPref(applicationContext, counter)
    buttonCounter.text = counter.toString()
    if (buttonCounter.text == 999.toString()) {
        counter = 0
        PrefConfig.saveTotalInPref(applicationContext, counter)
        buttonCounter.text = counter.toString()
    }
}

fun resetCounter(buttonCounter: Button) {
    counter = 0
    PrefConfig.saveTotalInPref(applicationContext, counter)
    buttonCounter.text = counter.toString()
  }
}

CounterActions 清单 class

        <activity
        android:name=".utils.helper.CounterActions"
        android:exported="true" />

HomeAdapter 并且我从 CounterActions 调用方法 class

    static class CounterViewHolder extends RecyclerView.ViewHolder {
    ItemHomeCounterBinding itemHomeCounterBinding;
    CounterActions counter = new CounterActions();

    CounterViewHolder(@NonNull ItemHomeCounterBinding itemView) {
        super(itemView.getRoot());
        itemHomeCounterBinding = itemView;
        counter.displayCounter(itemHomeCounterBinding.buttonCounter);
    }

    void setOnClick() {
        itemHomeCounterBinding.buttonCounter.setOnClickListener(v -> {
            counter.addCounter(itemHomeCounterBinding.buttonCounter);
            counter.vibrateOnce(itemView.getContext());
        });

        itemView.setOnClickListener(v -> {
            counter.addCounter(itemHomeCounterBinding.buttonCounter);
            counter.vibrateOnce(itemView.getContext());
        });

        itemHomeCounterBinding.resetButtonOnClick.setOnClickListener(v -> {
            counter.resetCounter(itemHomeCounterBinding.buttonCounter);
            counter.vibrateOnce(itemView.getContext());
        });
    }
}

错误代码

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.content.Context.getSharedPreferences(java.lang.String, int)' on a null object reference
    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:174)
    at com.moataz.afternoonhadeeth.utils.helper.PrefConfig.loadTotalFromPref(PrefConfig.kt:19)
    at com.moataz.afternoonhadeeth.utils.helper.CounterActions.<init>(CounterActions.kt:13)
    at com.moataz.afternoonhadeeth.ui.adapter.HomeAdapter$CounterViewHolder.<init>(HomeAdapter.java:339)
    at com.moataz.afternoonhadeeth.ui.adapter.HomeAdapter.onCreateViewHolder(HomeAdapter.java:88)

Answer 1

您的 CounterActions 未用作 Activity，因此不应扩展它（删除 : AppCompatActivity()）

class CounterActions {

同时删除相关清单条目

但是如何在里面得到合适的Context呢？只需从 buttonCounter 获取，每个 View 都需要 Context 才能创建。而View放在Activity里面，其实就是运行（通过system/user交互或者startActivity方法启动）

class CounterActions {

    fun displayCounter(buttonCounter: Button) {
        var counter = PrefConfig.loadTotalFromPref(buttonCounter.context)
        buttonCounter.text = counter.toString()
    }

    fun addCounter(buttonCounter: Button) {
        var counter = PrefConfig.loadTotalFromPref(buttonCounter.context)
        counter++
        PrefConfig.saveTotalInPref(buttonCounter.context, counter)
        buttonCounter.text = counter.toString()
        if (buttonCounter.text == 999.toString()) {
            resetCounter(buttonCounter)
        }
    }

    fun resetCounter(buttonCounter: Button) {
        counter = 0
        PrefConfig.saveTotalInPref(buttonCounter.context, counter)
        buttonCounter.text = counter.toString()
      }
}

空对象引用上的 Sharedpreferences Context()

Sharedpreferences Context() on a null object reference

android

nullpointerexception

kotlin