如何使用另一个 Activity 的 onBackPressed() 方法从 Activity 中清除/重置 SharedPreference？

Question

所以我将 SharedPreference 编码到（活动 1）中，它允许用户选择在应用启动时首先向他们呈现的活动。代码运行良好，但如果用户想要更改他们的选择怎么办？当用户按下后退按钮返回（活动 1）时，它会自动将他们重定向到他们之前选择的活动。当用户单击调用 onBackPressed() 方法的活动 2 上的“后退按钮”时，如何重置/清除（活动 1）中的共享首选项？

活动一

final SharedPreferences sharedPref = getPreferences(MODE_PRIVATE);
    int choice = sharedPref.getInt("default_activity", -1);


    if (choice == -1) {
        // show the option to choose the default activity to the user
        // e.g. dialog with list, then save the corresponding choice to
        // shared preference
        String[] activities = { "Activity 1", "Activity 2", "Activity 3" };

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setAdapter(
                new ArrayAdapter<String>(this,
                        android.R.layout.simple_list_item_1, activities),
                new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        SharedPreferences.Editor editor = sharedPref.edit();
                        editor.putInt("default_activity", which);

                        editor.apply();
                        launchActivity(which);
                    }
                }).show();
    } else {
        // start the activity and close this activity
        launchActivity(choice);
    }


}

private void launchActivity(int choice) {
    switch (choice) {
        case 0:
            startActivity(new Intent(this, Activity_1.class));
            break;
        case 1:
            startActivity(new Intent(this, Activity_2.class));
            break;
        case 2:
            startActivity(new Intent(this, Activity_3.class));
            break;
    }
    finish();
}

活动 2

@Override
public void onBackPressed() {
    super.onBackPressed();
    Intent i = new Intent (getApplicationContext(), PreActivity.class);
    startActivity(i);
}

Answer 1

经过数小时的研究和尝试，我找到了解决方案。

活动一

我将变量声明为静态

public static SharedPreferences sharedPref;

然后我更改了“GetPreferences”行代码

来自

final SharedPreferences sharedPref = getPreferences(MODE_PRIVATE);

到

sharedPref = getPreferences(MODE_PRIVATE);

然后我将其他所有内容都保留为相同的“活动 1”

 sharedPref = getPreferences(MODE_PRIVATE);
 int choice = sharedPref.getInt("default_activity", -1);


if (choice == -1) {
    // show the option to choose the default activity to the user
    // e.g. dialog with list, then save the corresponding choice to
    // shared preference
    String[] activities = { "Activity 1", "Activity 2", "Activity 3" };

    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.setAdapter(
            new ArrayAdapter<String>(this,
                    android.R.layout.simple_list_item_1, activities),
            new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    SharedPreferences.Editor editor = sharedPref.edit();
                    editor.putInt("default_activity", which);

                    editor.apply();
                    launchActivity(which);
                }
            }).show();
} else {
    // start the activity and close this activity
    launchActivity(choice);
   }
}



private void launchActivity(int choice) {
    switch (choice) {
        case 0:
            startActivity(new Intent(this, Activity_1.class));
            break;
        case 1:
            startActivity(new Intent(this, Activity_2.class));
            break;
        case 2:
            startActivity(new Intent(this, Activity_3.class));
            break;
    }
    finish();
}

然后在活动 2 和 3 中，我在 onBackPressed() 方法中添加了一行代码

活动 2 和 3

public void onBackPressed() {
        super.onBackPressed();
        Activity_2.sharedPref.edit().clear().commit(); // This line references 
                                      //"sharedPref" from the activity (Activity 2)
        Intent i = new Intent(getApplicationContext(), Activity_1.class);
        startActivity(i);
}

Answer 2

只需将重置共享偏好的代码放在活动 2 中即可。onBackPressed 应该会为您返回到上一个活动。

此外，您可能希望使用默认共享首选项来确保您访问的是相同的首选项存储：

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);

并在两个活动中使用这些首选项

 @Override
 public void onBackPressed() {
    PreferenceManager.getDefaultSharedPreferences(this).edit()
              .remove("default_activity")
              .apply()
   super.onBackPressed();
 }