java - Android:将 arrayList 保存到文件不起作用

Question

我有一个 Activity DrinkWater其中包含 recyclerView 。我正在尝试保存 arrayList命名data保存在内部存储中以供将来引用，但不知何故它不起作用。

我确实在 list 文件中添加了权限，所以这不是问题。

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

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

下面是 DrinkWater.java 的(简化)代码文件。我出于调试目的做了一些 Toast。因此不要错过//评论

    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 中可能出现的异常:“未知错误(代码 14)无法打开数据库。” 2.“此处不支持读取空字符串” 3.“列 context_id 不唯一(代码 19)”

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。

保存(没有异常处理代码):

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

尝试一下，然后告诉我这是否适合您。

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