Android：如果 - 否则收到意向

Question

我正在尝试使用 "Database is now updated" 创建返回主页并启动主页屏幕的活动。但是，只有在收到意图时，我才知道如何吐司。但是我不确定如何很好地接收 Intent，这是我的代码。

public class MainActivity extends Activity {

TextView time;
Button viewStock, descriptionSearch;
String lastUpdateStandard = "Last Update Time: ";

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

    viewStock = (Button) findViewById(R.id.detailSearchButton);
    descriptionSearch = (Button) findViewById(R.id.descriptionSearchButton);
    time = (TextView) findViewById(R.id.time);

    // retrieve time from database to see last update time
    DatabaseHandler db = new DatabaseHandler(getApplicationContext());
    List<String> lastUpdateTime = db.getLastUpdate();
    time.setText(lastUpdateStandard + lastUpdateTime.get(0));

    Intent receivedIntent = getIntent();
    /**
     *
     * What should I write if there is no received Intent? 
     * Probably I need an if-else statement, but I have no idea how it should be made. 
     */
}

Answer 1

不建议您当前想要执行的检查类型，因为所有活动都是由一个意图启动的（Android 是这样设计的），它们总是 return 一个意图。相反，您应该做的是检查用于启动 activity 的意图是否包含您希望提取的数据。您显然只需要意图，因为您需要来自意图的某种数据，对吗？因此，与其检查意图是否被 returned，不如检查从意图中获得的任何额外信息。例如，如果您想使用字符串 "hello" 作为键来提取额外内容，您将使用：

Intent receivedIntent = getIntent();
if(receivedIntent.getStringExtra("hello") != null) {
    // Means the intent has the data you expect
} else {
    // It does not have the data you expect
    // Do some processing here
}

如果你要检查是否收到了一个意图，你总是会得到一个值

Android：如果 - 否则收到意向

Android: Intent Received if - else

android

android-intent