如何在 android 中从 'outside' 强制更新主 activity？

Question

此问题是 this 未回答问题的后续问题，包含更多更好的细节。

基本上，我有一个 android 主 activity 显示一些从数据库中获取的数据（通过 SQLiteDatabase）。现在我有一个 PreferenceActivity ，当用户想要更改某些偏好或删除数据库的内容时会显示它。在后一种情况下，数据库的内容被删除了——但是我该如何更新主 activity 呢？如果我在按下删除数据库内容的按钮后查看 main activity，我希望显示 main activity 零条目！

这里是正文的相关部分activity：

public class MainActivity extends AppCompatActivity  {

    SharedPreferences.OnSharedPreferenceChangeListener mPrefListener;
    private SharedPreferences settings;
    public interface MyCallBack
    {
        public void refreshMainActivity();
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Intent intent = new Intent(this, AlarmService.class);
        startService(intent);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        mCallback = new MyCallBack() {
            @Override
            public void refreshMainActivity() {
                Toast.makeText(MainActivity.this, "TOAST MAINACTIVITY", Toast.LENGTH_LONG).show();
                MainActivity.this.recreate();
            }
        };
        /*
        settings = PreferenceManager.getDefaultSharedPreferences(this);
        mPrefListener = new SharedPreferences.OnSharedPreferenceChangeListener() {
            @Override
            public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
                Log.d("TEST", "testtest");

                Toast.makeText(MainActivity.this, "TOAST MAINACTIVITY", Toast.LENGTH_LONG).show();

                finish();
                startActivity(getIntent());
            }
        };
        */

        // Register the listener on the SharedPreferences
        settings.registerOnSharedPreferenceChangeListener(mPrefListener);

这里是UserSettingActivity.java的内容：

public class UserSettingActivity extends PreferenceActivity {

    private Preference myPreference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
        myPreference = findPreference("reset");
        myPreference.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
            public boolean onPreferenceClick(Preference arg0) {
                AlertDialog.Builder alertDialog = new AlertDialog.Builder(UserSettingActivity.this);
                alertDialog.setMessage("Are you sure to delete the database?");
                alertDialog.setCancelable(true);
                alertDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        final DBAdapter db = new DBAdapter(UserSettingActivity.this);
                        db.open();
                        db.resetDatabase();
                        callBack = MainActivity.mCallback;
                        callBack.refreshMainActivity();
                    } });
                alertDialog.setNegativeButton("No", new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                    } });
                alertDialog.show();
                return false;
            }
        });

    }

}

最后，xml 文件描述了 xml/preferences.xml 中设置的布局：

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
    <EditTextPreference android:title="Your Name"
        android:key="username"
        android:summary="Please provide your username"></EditTextPreference>
    <CheckBoxPreference android:title="Application Updates"
        android:defaultValue="false"
        android:summary="This option if selected will allow the application to check for latest versions."
        android:key="applicationUpdates" />

    <Preference
        android:key="reset"
        android:title="Reset database"
        android:summary="This will remove every entry in the database"
         />
</PreferenceScreen>

当我在“设置”屏幕上单击按钮 reset 并确认此选择时，数据库被删除 resetDatabase 执行 DROP 和 CREATE TABLE数据库中的两个表）。但是，Toast 'TOAST MAINACTIVITY' 从未显示在显示屏上！

要使这项工作如我所愿，我在这里错过了什么？如何从 UserSettingActivity?

中触发主 activity 中的 method/function/something

Answer 1

使用回调的解决方案可能有点棘手，但我希望根据您的情况这对您有用..

首先在你的MainActivity.java中创建界面，像这样

public interface MyCallBack
{
 public void refreshMainActivity();
}

然后像这样在你的主 activity 中实现这个接口

public class MainActivity extends AppCompatActivity {
public static MyCallBack mCallback;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

mCallback = new MyCallBack() {
    @Override
    public void refreshMainActivity() {
           MainActivity.this.recreate();

              "OR"

              finish();
              startActivity(getIntent());
         }
    };
}

现在在你的 userSettingActivity.java 中使用这个接口，当你想更新你的 MainActivity.java

时调用它的方法

public class UserSettingActivity extends AppCompatActivity{
MainActivity.MyCallBack callBack;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.settingsactivity);
    callBack = MainActivity.mCallback;

    //this is sample code ..call this function when you want to update mainactivity
    callBack.refreshMainActivity();
}

}

如何在 android 中从 'outside' 强制更新主 activity？

How to force an update of the main activity from 'outside' in android?

java

xml

android

android-activity

android-settings