我有2个活动: - LoginActivity:它将在以后处理登录内容 - 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,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,这就是它应该如何工作,它不能通过简单的后退按钮返回到登录屏幕。
但是现在如果我点击退出(并显示登录屏幕),然后我按下后退按钮,应用程序会将我带回主屏幕,这真的不合适。如果我退出,则从登录屏幕返回按钮应该关闭应用程序。
另一个问题,关于backstack和片段: 我有3个片段:第一,第二和第三。如果我在彼此之后打开它们(当然是在主要活动中),然后按下后退按钮,我希望它将我带回到之前打开的片段,或者如果之前没有,请关闭应用程序。 现在它创建它,打开上一个片段,但同时它关闭了完整的应用程序。 (我可以看到他们正在发生在彼此之后)
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:
MainActivity:
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();
}
}
LoginActivity:
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();
}
}
答案 0 :(得分:1)
关于在Activities
之间切换。
一件重要的事情。
在showActivity()
时使用finish()
来转移到另一个时杀死当前Activity
。如果它没有帮助 - 见下文。
尝试同时使用FLAG_ACTIVITY_NEW_TASK
当前的标记,因为FLAG_ACTIVITY_CLEAR_TOP
只会关闭当前活动以上任务中的活动,但不会关闭。
所以,就是这样:intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK);
另一种选择是仅使用:FLAG_ACTIVITY_CLEAR_TASK
- 新活动将清除任务并成为其中的根。
如果两者都没有帮助 - 在每份android:launchMode = "singleInstance"
的清单中使用Actitivy
。
关于Fragments
- 我在您的代码中看到了一个小错误:它在super.onBackPressed();
Fragment
中弹出BackStack
之前调用了@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else if (getFragmentManager().getBackStackEntryCount() > 0 ){
getFragmentManager().popBackStack();
} else {
super.onBackPressed();
}
}
我会这样改变:
getFragmentManager().getBackStackEntryCount() > 0
!! 此外,您应该测试此行:0
条件1
和FragmentContainer
条件(因为在我的项目{{1}中的当前实现中}首先考虑BackStack
中的零值。只需测试0和1即可查看哪些有效。
感谢。
的 PS。更多提示。
您可以在FragmentManager fragmentManager
中声明Activity
,以便仅在onCreate()
中创建一次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) {
}
。这比每次都更好。(
考虑改变这个:
switch (item.getItemId()) {
case R.id.nav_first_layout:
showFragment(new FirstFragment(), "FirstFragment");
break;
case ...
}
要:
<com.example.myapplication.CustomTextView
android:id="@+id/tvScrollingMessage"
android:text="@string/scrolling_message_main_wish_list"
android:singleLine="true"
android:ellipsize="marquee"
android:marqueeRepeatLimit ="marquee_forever"
android:focusable="true"
android:focusableInTouchMode="true"
android:scrollHorizontally="true"
android:layout_width="match_parent"
android:layout_height="40dp"
android:background="@color/black"
android:gravity="center"
android:textColor="@color/white"
android:textSize="15dp"
android:freezesText="true"/>
等等。代码会更漂亮:))