java - 通过 Bundle 在 Activity 之间保留值

Question

我正在使用以下方法在 Activity 之间保存用户输入的变量:

  // Save instance between activities
    @Override
    public void onSaveInstanceState(Bundle savedInstanceState)
    {

        Toast.makeText(searchParam.this, "onSaveInstanceState", Toast.LENGTH_SHORT).show();
        savedInstanceState.putString("subject", selectedSubject);
        savedInstanceState.putString("priceBand", priceBand);
        savedInstanceState.putFloat("rating", starRating);
        savedInstanceState.putBoolean("isCheck", checked);
        super.onSaveInstanceState(savedInstanceState);
    }

当用户选择高级选项时，他/她将被发送到 advancedSearch.class 以通过此方法执行其他操作:

 public void listenerForAdvSearch()
    {
        // Initialize advanced options button
        Button advancedOptionsBtn = (Button) findViewById(R.id.advancedButton);
        advancedOptionsBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent advancedOptions = new Intent(searchParam.this, advancedSearch.class);
                startActivity(advancedOptions);
            }
        });
    }

返回时我的 onCreate 方法被调用如下:

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


        setContentView(R.layout.activity_main);

        Toast.makeText(searchParam.this, "onCreate called", Toast.LENGTH_LONG).show();
         if (savedInstanceState != null)
         {
            Toast.makeText(searchParam.this, "if savedInstanceState != NULL", Toast.LENGTH_LONG).show();
            selectedSubject = savedInstanceState.getString("subject");
            priceBand = savedInstanceState.getString("priceBand");
            checked = savedInstanceState.getBoolean("isCheck");
            starRating = savedInstanceState.getFloat("rating");
         }
         else
            Toast.makeText(searchParam.this, "if savedInstanceState = NULL", Toast.LENGTH_SHORT).show();

        // Call all listeners
        listenerForRatingBar();
        listenerForSubject();
        listenerForSearch();
        listenerForAdvSearch();
        listenerForGeoCheck();
        listenerForPrice();

    }

我在其中有几条 toast 消息用于我的个人调试。我的问题出在 onCreate 方法中的 if 语句中； savedInstanceState 包返回为 NULL，并且不恢复从高级选项类返回的值。为什么会这样？

注意:这里是advancedSearch类的相关代码:

public class advancedSearch extends AppCompatActivity {

    // initialize variables
    int minute_x, hour_x;
    int year_x, month_x, day;
    static final int dialogid = 0;
    static final int tdialogid = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_advanced_search);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        // Call picker dialogs on button click
        showDialogOnButtonClick();
        showTimeDialogOnButtonClick();

    }

Answer 1

您需要将 Bundle 添加到您从中启动 Activity 的 Intent。 onSaveInstanceState() 在这里不起作用。在另一个 Activity 中，使用 getIntent().getExtras() 获取 Bundle 以提取您添加的值。

onSaveInstanceState() 用于在您所在的 Activity 的重新创建或配置更改期间恢复 Activity 状态，而不是跨越 Activity 到 Activity。

即:

删除对 onSaveInstanceState() 的覆盖。

启动新的Activity时，将需要的数据传入Intent:

public void listenerForAdvSearch()
{
    // Initialize advanced options button
    Button advancedOptionsBtn = (Button) findViewById(R.id.advancedButton);
    advancedOptionsBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
             Intent advancedOptions = new Intent(searchParam.this, advancedSearch.class);
             advancedOptions.putExtra("subject", selectedSubject);
             advancedOptions.putExtra("priceBand", priceBand);
             advancedOptions.putExtra("rating", starRating);
             advancedOptions.putExtra("isCheck", checked);
             startActivity(advancedOptions);
         }
     });
}

在您的新 Activity 中，从 Intent 中的 Bundle 获取数据:

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toast.makeText(searchParam.this, "onCreate called", Toast.LENGTH_LONG).show();

    //Get your precious data
    Bundle bundle = getIntent().getExtras();
    selectedSubject = bundle.getString("subject");
    priceBand = bundle.getString("priceBand");
    checked = bundle.getBoolean("isCheck");
    starRating = bundle.getFloat("rating");

    // Call all listeners
    listenerForRatingBar();
    listenerForSubject();
    listenerForSearch();
    listenerForAdvSearch();
    listenerForGeoCheck();
    listenerForPrice();

}