Android：无法将 arrayList 保存到文件

Question

我有一个包含 recyclerView 的 activity DrinkWater。我正在尝试将名为 data 的 arrayList 保存到内部存储中的文件以供将来参考，但不知何故它不起作用。

我确实在 Manifest 文件中添加了权限，所以这不是问题所在。

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

下面是 DrinkWater.java 文件的（简化）代码。为了调试目的，我做了几个 Toast。因此不要错过 //comments

    public class DrinkWater extends ActionBarActivity {

Toolbar toolbar;
private RecyclerView recyclerView;
private InfoTodayAdapter adapter;
FileOutputStream fos;
FileInputStream fis;
List<InformationToday> data = new ArrayList<>();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_drink_water);

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

    recyclerView = (RecyclerView) findViewById(R.id.recyclerview_today);
    adapter = new InfoTodayAdapter(this,getData());
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
}

public List<InformationToday> getData(){
    try {
        fis = getBaseContext().openFileInput("arrayListToday");
        ObjectInputStream ois = new ObjectInputStream(fis);
        //Below Toast just for debugging. 
        Toast.makeText(this,"Try block for read data called 1",Toast.LENGTH_SHORT).show(); 
        data = (List<InformationToday>) ois.readObject(); // Cause of the error. 
        //Below toast for debugging. But it is never executed.
        Toast.makeText(this,"Try block for read data called 2",Toast.LENGTH_SHORT).show();  
        ois.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
        Log.d("TAG A","arrayListToday file not found");
    } catch (Exception e){
        Log.d("TAG A","Exception generated 1");
    }
    return data;
}


public void addWater(View view) {   // This method adds data to the recyclerView. It is called by on click of the Floating Action Button
    InformationToday i = new InformationToday();
    if(view.getId() == R.id.fifty_button)
    {
        i.volume = "50";
        Log.d("TAG A","i.volume = 50");
    }
    else
    {
        i.volume = "100";
    }
    data.add(0,i);          
    adapter.update(data);   //This method is described in recyclerView adapter. It updates the recyclerView data.
    try {
        fos = getBaseContext().openFileOutput("arrayListToday",Context.MODE_PRIVATE);
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        Toast.makeText(this,"Try block for wrtie data called 1",Toast.LENGTH_SHORT).show(); //For debugging.
        oos.writeObject(data); // Cause of the error. 
        Toast.makeText(this,"Try block for write data called 2",Toast.LENGTH_SHORT).show(); //For debugging. It is never executed.
        oos.close();
    } catch (FileNotFoundException e) {
        Toast.makeText(this,"Catch: File not gound exception",Toast.LENGTH_SHORT).show();
        Log.d("TAG A", "Catch: File not found");
        e.printStackTrace();
    }catch (Exception e){
        Toast.makeText(this,"Catch: Exception e",Toast.LENGTH_SHORT).show();
        Log.d("TAG A","Catch: Exception e");
    }
    com.getbase.floatingactionbutton.FloatingActionsMenu f = (FloatingActionsMenu) findViewById(R.id.multiple_actions);
    f.collapseImmediately();

}
}

没有这样的错误。但 Logcat 的可能例外："unknown error (code 14) could not open database." 2. "Reading a null string not supported here" 3."column context_id is not unique (code 19)"

所以解决错误（代码 14）无法打开数据库的问题没有帮助。

Answer 1

您必须序列化对象，然后将它们写入文件。

正在保存（w/o异常处理代码）：

FileOutputStream fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
ObjectOutputStream os = new ObjectOutputStream(fos);
os.writeObject(data);
os.close();
fos.close();

试试这个，如果它适合你，请告诉我。

Reference Link

Android：无法将 arrayList 保存到文件

Android: Saving arrayList to file not working

java

android

file

arraylist

save