【发布时间】：2016-04-16 11:00:29
【问题描述】：
我有 2 个活动： - LoginActivity：稍后将处理登录内容 - MainActivity：主应用程序，所有功能都将在片段上提供。
我想正确使用后台堆栈，但我不能。
我想要（但不能）实现的目标： 应用程序从登录屏幕开始。我登录（现在按下开始按钮），然后出现主屏幕并加载第一个片段。 现在，如果我按下后退按钮，应用程序将关闭，它应该是这样工作的，它不能通过简单的后退按钮返回到登录屏幕。
但是现在如果我单击注销（并出现登录屏幕），然后按后退按钮，应用程序会将我带回主屏幕，这真的不行。如果我退出，从登录屏幕返回按钮应该关闭应用程序。
还有一个问题，关于 backstack 和 Fragments： 我有 3 个片段：第一个、第二个和第三个。如果我一个接一个地打开它们（当然是在主要活动中），并且我按下后退按钮，我希望它带我回到之前打开的片段，或者如果没有之前的片段，请关闭应用程序。 现在它成功了，打开了前一个片段，但同时关闭了整个应用程序。 （我可以看到它们是紧接着发生的）
缺少什么？应该修改什么来实现这种（正常）行为？
谢谢！
我的代码：
主活动：
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
public static final String SP_DATA = "SP_DATA";
public static final String FB_LOGIN_STATUS = "FB_LOGIN_STATUS";
public static final String FLRT = "FLRT";
public SharedPreferences sharedPreferences;
@Override
protected void onCreate(Bundle savedInstanceState) {
sharedPreferences = getSharedPreferences(SP_DATA, MODE_PRIVATE);
boolean bAlreadyLoggedIn = sharedPreferences.getBoolean(FB_LOGIN_STATUS, false);
if (bAlreadyLoggedIn) {
Log.d(FLRT, "Already logged in");
}
else {
Log.d(FLRT, "Not logged in");
Intent intent = new Intent(MainActivity.this, LoginActivity.class);
startActivity(intent);
}
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
showFragment(new FirstFragment(),"FirstFragment");
Button btnLogout = (Button) findViewById(R.id.btnLogout);
btnLogout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
logout();
showActivity(MainActivity.this, LoginActivity.class);
}
});
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
private void showActivity(Context context_fromActivity, Class<?> class_toActivty){
Intent intent = new Intent(context_fromActivity, class_toActivty);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
}
private void logout() {
Log.d(FLRT, "Logging out...");
sharedPreferences = getSharedPreferences(SP_DATA, MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putBoolean(FB_LOGIN_STATUS, false);
editor.commit();
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
if (getFragmentManager().getBackStackEntryCount() > 0 ){
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_first_layout) {
showFragment(new FirstFragment(), "FirstFragment");
}
else if (id == R.id.nav_second_layout) {
showFragment(new SecondFragment(), "SecondFragment");
}
else if (id == R.id.nav_third_layout) {
showFragment(new ThirdFragment(), "ThirdFragment");
}
else if (id == R.id.nav_share) {
}
else if (id == R.id.nav_send) {
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
private void showFragment(Fragment fragment, String sFragmentTAG) {
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
if (fragmentManager.findFragmentByTag(sFragmentTAG) != null) {
Log.d(FLRT, "Fragment found, using existing one: " + sFragmentTAG);
fragment = fragmentManager.findFragmentByTag(sFragmentTAG);
}
fragmentTransaction.replace(R.id.fragmentContainer, fragment, sFragmentTAG);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
}
登录活动：
public class LoginActivity extends AppCompatActivity {
public static final String SP_DATA = "SP_DATA";
public static final String FB_LOGIN_STATUS = "FB_LOGIN_STATUS";
public static final String FLRT = "FLRT";
public SharedPreferences sharedPreferences;
private Button btn_start;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
btn_start = (Button) findViewById(R.id.btn_start);
btn_start.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
login();
showActivity(LoginActivity.this, MainActivity.class);;
}
});
}
private void showActivity(Context context_fromActivity, Class<?> class_toActivty){
Intent intent = new Intent(context_fromActivity, class_toActivty);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
}
private void login() {
Log.d(FLRT, "Logging in...");
sharedPreferences = getSharedPreferences(SP_DATA, MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putBoolean(FB_LOGIN_STATUS, true);
editor.commit();
}
}
【问题讨论】：
标签： android android-fragments back-stack fragment-backstack