我在一个计数程序中遇到一个问题，该问题显示了调用诸如onCreate，onStart等方法的次数，当我从Activity1转到Activity2然后又回到Activity1时，它似乎运行良好，但是当我切换方向时，仅mResume增加。
因此，例如，当我启动应用程序并切换方向3次时，结果如下所示：
onCreate() calls:1
onStart() calls:1
onResume() calls:4
onRestart() calls:1
另一个奇怪的事情是，当我从onRestoreInstanceState注释掉mResume，mRestart和mStart时，突然有两个变量更新了mStart和mResume。
public void onRestoreInstanceState(Bundle savedInstanceState) {
// Always call the superclass so it can restore the view hierarchy
super.onRestoreInstanceState(savedInstanceState);
Log.i(TAG, "Entered the onRestoreInstanceState() method");
// Restore state members from saved instance
//mResume = savedInstanceState.getInt(RESUME_KEY);
//mRestart = savedInstanceState.getInt(RESTART_KEY);
//mStart = savedInstanceState.getInt(START_KEY);
mCreate = savedInstanceState.getInt(CREATE_KEY);
这是完整的代码
public class ActivityOne extends Activity {
// Use these as keys when you're saving state between reconfigurations
private static final String RESTART_KEY = "restart";
private static final String RESUME_KEY = "resume";
private static final String START_KEY = "start";
private static final String CREATE_KEY = "create";
// String for LogCat documentation
private final static String TAG = "Lab-ActivityOne";
// Lifecycle counters
// TODO:
// Create variables named
// mCreate, mRestart, mStart and mResume
// to count calls to onCreate(), onRestart(), onStart() and
// onResume(). These variables should not be defined as static.
// You will need to increment these variables' values when their
// corresponding lifecycle methods get called.
int mCreate;
int mRestart;
int mStart;
int mResume;
// TODO: Create variables for each of the TextViews
// named mTvCreate, mTvRestart, mTvStart, mTvResume.
// for displaying the current count of each counter variable
TextView mTvCreate;
TextView mTvRestart;
TextView mTvResume;
TextView mTvStart;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_one);
// TODO: Assign the appropriate TextViews to the TextView variables
// Hint: Access the TextView by calling Activity's findViewById()
// textView1 = (TextView) findViewById(R.id.textView1);
mTvCreate = (TextView) findViewById(R.id.create);
mTvRestart = (TextView) findViewById(R.id.restart);
mTvStart = (TextView) findViewById(R.id.start);
mTvResume = (TextView) findViewById(R.id.resume);
Button launchActivityTwoButton = (Button) findViewById(R.id.bLaunchActivityTwo);
launchActivityTwoButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO:
// Launch Activity Two
// Hint: use Context's startActivity() method
// Create an intent stating which Activity you would like to
// start
Intent intent = new Intent(v.getContext(), ActivityTwo.class);
// Launch the Activity using the intent
startActivity(intent);
}
});
// Has previous state been saved?
if (savedInstanceState != null) {
// TODO:
// Restore value of counters from saved state
// Only need 4 lines of code, one for every count variable
mCreate = savedInstanceState.getInt(CREATE_KEY);
mRestart = savedInstanceState.getInt(RESTART_KEY);
mStart = savedInstanceState.getInt(START_KEY);
mResume = savedInstanceState.getInt(RESUME_KEY);
}
// Emit LogCat message
Log.i(TAG, "Entered the onCreate() method");
// TODO:
// Update the appropriate count variable
// Update the user interface via the displayCounts() method
mCreate += 1;
displayCounts();
}
// Lifecycle callback overrides
@Override
public void onStart() {
super.onStart();
// Emit LogCat message
Log.i(TAG, "Entered the onStart() method");
// TODO:
// Update the appropriate count variable
// Update the user interface
mStart += 1;
displayCounts();
}
@Override
public void onResume() {
super.onResume();
// Emit LogCat message
Log.i(TAG, "Entered the onResume() method");
// TODO:
// Update the appropriate count variable
// Update the user interface
mResume += 1;
displayCounts();
}
@Override
public void onPause() {
super.onPause();
// Emit LogCat message
Log.i(TAG, "Entered the onPause() method");
}
@Override
public void onStop() {
super.onStop();
// Emit LogCat message
Log.i(TAG, "Entered the onStop() method");
}
@Override
public void onRestart() {
super.onRestart();
// Emit LogCat message
Log.i(TAG, "Entered the onRestart() method");
// TODO:
// Update the appropriate count variable
// Update the user interface
mRestart += 1;
displayCounts();
}
@Override
public void onDestroy() {
super.onDestroy();
// Emit LogCat message
Log.i(TAG, "Entered the onDestroy() method");
}
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
Log.i(TAG, "Entered the onSaveInstanceState() method");
// TODO:
// Save state information with a collection of key-value pairs
// 4 lines of code, one for every count variable
savedInstanceState.putInt(CREATE_KEY, mCreate);
savedInstanceState.putInt(RESTART_KEY, mRestart);
savedInstanceState.putInt(START_KEY, mStart);
savedInstanceState.putInt(RESUME_KEY, mResume);
}
public void onRestoreInstanceState(Bundle savedInstanceState) {
// Always call the superclass so it can restore the view hierarchy
super.onRestoreInstanceState(savedInstanceState);
Log.i(TAG, "Entered the onRestoreInstanceState() method");
// Restore state members from saved instance
mResume = savedInstanceState.getInt(RESUME_KEY);
mRestart = savedInstanceState.getInt(RESTART_KEY);
mStart = savedInstanceState.getInt(START_KEY);
mCreate = savedInstanceState.getInt(CREATE_KEY);
//displayCounts();
}
// Updates the displayed counters
// This method expects that the counters and TextView variables use the
// names
// specified above
public void displayCounts() {
mTvCreate.setText("onCreate() calls: " + mCreate);
mTvStart.setText("onStart() calls: " + mStart);
mTvResume.setText("onResume() calls: " + mResume);
mTvRestart.setText("onRestart() calls: " + mRestart);
}
}
这是XML
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView android:id="@+id/create"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/onCreate" />
<TextView android:id="@+id/start"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/onStart" />
<TextView android:id="@+id/resume"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/onResume" />
<TextView android:id="@+id/restart"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/onRestart" />
<Button android:id="@+id/bLaunchActivityTwo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button" />
</LinearLayout>
最佳答案
您将在mCreate和mStart中两次从mRestart对象获取mResume，Bundle，onCreate和onRestoreInstanceState的值。这意味着两次检索值之间对计数所做的任何更改都将被忽略。
如果完全调用了onRestoreInstanceState，则在onCreate之后调用onRestoreInstanceState，因此您不应该还原onCreate中的值，因为它们已经在中还原了。