问题
I am working on an Android application that requires a user to login before doing anything else. Currently I have created main Activity named LoginScreen and upon successful login this activity launches another Activity called Home. But I see a problem with this approach. What if user presses back button from Home activity? I dont want user going back to login screen. what is the correct way of stopping the user from doing that. Do I need to handle Key Press events?
回答1:
What I ended up doing was to make my Home activity handle the intent android.intent.action.MAIN. Home activity, when launched, checks if the user is signed in or not (using shared preferences), if its not then it starts LoginActivity and calls finish() on its self.
LoginActivity on successful login starts the Main activity and this time because the user is logged on, the Main activity will continue its normal course. LoginActivity is declared as following in the manifest file:
<activity android:name="LoginScreen" android:label="@string/app_name"
android:noHistory="true" android:excludeFromRecents="true">
</activity>
Setting noHistory and excludeFromRecents to true for LoginActivity means that the user cant return to this activity using back button.
回答2:
After you call startActivity(...) in the LoginScreen activity, call finish(). This will remove that activity from the activity stack, so pressing back will essentially close your app once you're in your Home activity.
回答3:
Try setting flags to the Intent.
Example:
new Intent(context, SomeActivity.class).setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
More information on flags: http://developer.android.com/reference/android/content/Intent.html#nestedclasses
回答4:
See: https://stackoverflow.com/a/41290453/4560689 (text below)
To do this, you should create a single launcher activity with No Display (using Android's NoDisplay theme), that runs the logic of whether to go to the home screen or to log in/register.
First, in your manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.example.android">
<-- Permissions etc -->
<application
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name">
<activity
android:name=".onboarding.StartupActivity"
android:label="@string/app_name"
android:launchMode="singleInstance"
android:theme="android:style/Theme.NoDisplay">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:launchMode="singleTop" />
<activity
android:name=".authentication.controller.AuthenticationActivity"
android:label="@string/title_sign_in"
android:launchMode="singleTask"
android:windowSoftInputMode="adjustResize|stateHidden" />
<-- Other activities, services, etc -->
</application>
Then, your StartupActivity:
package com.example.android.onboarding;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import com.example.android.MainActivity;
import com.example.android.authentication.controller.AuthenticationActivity;
import com.example.android.util.ResourceUtils;
public class StartupActivity extends Activity {
private static final AUTHENTICATION_REQUEST_CODE = 1000;
@Override
protected void onCreate(Bundle savedInstanceState) {
if (isLoggedIn()) {
Intent startupIntent = new Intent(this, MainActivity.class);
startupIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(startupIntent);
finish();
} else {
Intent startupIntent = new Intent(this, AuthenticationActivity.class);
startActivityForResult(startupIntent, AUTHENTICATION_REQUEST_CODE);
}
super.onCreate(savedInstanceState);
}
private boolean isLoggedIn() {
// Check SharedPreferences or wherever you store login information
return this.getSharedPreferences("my_app_preferences", Context.MODE_PRIVATE).getBoolean("loggedIn", false);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == AUTHENTICATION_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
Intent startupIntent = new Intent(this, MainActivity.class);
startupIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(startupIntent);
}
finish();
}
}
Gist here: https://gist.github.com/chanakin/c44bf1c6a9a80d2640440b5aaa92c8ee
回答5:
LoginActivity.xml
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fitsSystemWindows="true"
android:background="#263238">
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="80dp"
android:paddingLeft="16dp"
android:paddingRight="16dp">
<!-- App Logo -->
<ImageView android:id="@+id/logo"
android:src="@drawable/logo"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:layout_marginBottom="20dp"
android:layout_gravity="center_horizontal" />
<!--Title TextView-->
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="STOCK BUDDY"
android:id="@+id/title"
android:textSize="24sp"
android:textStyle="bold"
android:textColor="#7B869B"
android:layout_marginBottom="24dp"
android:layout_gravity="center_horizontal"/>
<!--User Email-->
<EditText
android:id="@+id/login_email"
android:layout_marginTop="10dp"
android:layout_marginBottom="5dp"
android:layout_centerVertical="true"
android:layout_width="match_parent"
android:layout_height="40dp"
android:ellipsize="start"
android:gravity="center"
android:hint="Email"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:textColorHint="#cccccc"
android:textColor="#7B869B"
android:maxLength="40"
android:maxLines="1"
android:inputType="textEmailAddress"
android:background="@drawable/edittextshape"/>
<!-- User Password -->
<EditText
android:id="@+id/login_password"
android:layout_marginTop="5dp"
android:layout_marginBottom="10dp"
android:layout_centerVertical="true"
android:layout_width="match_parent"
android:layout_height="40dp"
android:ellipsize="start"
android:gravity="center"
android:paddingRight="16dp"
android:paddingLeft="16dp"
android:hint="Password"
android:textColor="#7B869B"
android:textColorHint="#cccccc"
android:maxLength="20"
android:maxLines="1"
android:inputType="textPassword"
android:background="@drawable/edittextshape"/>
<!--Login Button-->
<android.support.v7.widget.AppCompatButton
android:id="@+id/btn_login"
android:layout_width="fill_parent"
android:layout_marginTop="5dp"
android:layout_marginBottom="24dp"
android:background="@drawable/buttonshape"
android:text="Login"
android:textSize="20sp"
android:layout_height="40dp"
android:textColor="#ffffff"
android:shadowRadius="5"
android:onClick="Login"/>
<!--signup Link TextView-->
<TextView android:id="@+id/link_signup"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="24dp"
android:text="No account yet? Create one"
android:gravity="center"
android:textSize="12sp"
android:textColor="#7B869B"/>
</LinearLayout>
</ScrollView>
buttonshape.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >
<corners
android:radius="44dp"
/>
<gradient
android:angle="45"
android:centerX="35%"
android:centerColor="#63D0C3"
android:startColor="#70DB9A"
android:endColor="#56C5EE"
android:type="linear"
/>
<padding
android:left="0dp"
android:top="0dp"
android:right="0dp"
android:bottom="0dp"
/>
<stroke
android:width="0dp"
android:color="#878787"
/>
</shape>
edittextshape.xml
<?xml version="1.0" encoding="utf-8" ?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:thickness="0dp"
android:shape="rectangle">
<solid android:color="#ffffff"/>
<stroke android:width="1dp"
android:color="#ffffff" />
<corners android:radius="44dp" />
</shape>
.....................
please see full code on https://androidpugnator.wordpress.com/2017/03/12/android-login-and-signup-screens
Image of login Screen
回答6:
Call startActivity(...) in the LoginActivity on some event(say login button click ). Use a separate database class also to store username and password of user from HomeActivity class.
Handle the onKeyDown() event for controlling back button in HomeActivity(use finish() method).
In OnCreate() method of LoginActivity class use database connection to check whether the username & password already exist in the database table if yes then call startActivity() there too to directly go to HomeScreen from LoginScreen.This will not show the LoginScreen.
Hope this will work for you. Try it.
来源：https://stackoverflow.com/questions/5859095/what-is-the-correct-way-of-creating-a-login-screen-activity-in-android