android - 一旦登录成功，Android 初始登录屏幕然后使用片段在屏幕之间滑动
问题描述
我正在尝试创建一个 Android 应用程序，然后有一个初始登录屏幕来检测用户是管理员还是用户。登录后，用户（取决于他们的角色）将看到不同的选项卡在不同的选项卡之间滑动。我有一个基本的应用程序，它以登录活动和登录来解密用户角色（目前使用静态值）。第一部分没问题。现在，当我在登录屏幕后尝试使用 Fragments 时，我被卡住了。
I have a LoginActivity that has an onClikcListener on a button after user enters credentials. Depending on whether the user is Amin or General Users, it will just to a new activity either activity_vote_admin or activity_vote_user. At this point I am stuck. Any ideas if what I am trying to do is valid. Or is there a better way to do this. At the moment I am getting this error.
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.confidencevotefragmentrebuild/com.example.confidencevotefragmentrebuild.activity_vote_admin}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference.
LoginActivity (this is my main activity)
...
package com.example.confidencevotefragmentrebuild;
import android.content.Intent;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class LoginActivity extends AppCompatActivity {
private static EditText username;
private static EditText password;
public static TextView attempts;
private static Button submit_button;
int attempt_counter = 5;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
loginButton();
}
public void loginButton() {
username = (EditText) findViewById(R.id.editText);
password = (EditText) findViewById(R.id.editText2);
attempts = (TextView) findViewById(R.id.textView_Attempts);
//Reference button view
final Button submit_button = findViewById(R.id.submit_button);
// perform click event on button
submit_button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (username.getText().toString().equals("admin") &&
password.getText().toString().equals("pass")) {
Toast.makeText(LoginActivity.this, "Welcome " + username.getText(),
Toast.LENGTH_SHORT).show();
Intent intent = new Intent(LoginActivity.this, activity_vote_admin.class);
startActivity(intent);
} else if (username.getText().toString().equals("user") &&
password.getText().toString().equals("pass")) {
Toast.makeText(LoginActivity.this, "Welcome " + username.getText(),
Toast.LENGTH_SHORT).show();
Intent intentUser = new Intent(LoginActivity.this, activity_vote_user.class);
startActivity(intentUser);
} else {
Toast.makeText(LoginActivity.this, "User or Password incorrect",
Toast.LENGTH_SHORT).show();
attempt_counter--;
attempts.setText(Integer.toString(attempt_counter));
if (attempt_counter == 0) {
Toast.makeText(LoginActivity.this, "Too many failed attempts, please close app and try again",
Toast.LENGTH_SHORT).show();
submit_button.setEnabled(false);
}
}
}
}
);
}
}
...
Activity_vote_admin
...
package com.example.confidencevotefragmentrebuild;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.RatingBar;
import android.widget.Spinner;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;
public class activity_vote_admin extends AppCompatActivity {
/**
* Field for selecting the number of confidence votes
*/
RatingBar mResults;
private RatingBar rBar;
Button mBtn;
/**
* Spinner field to enter the project name
*/
private Spinner mProjectSpinner;
/**
* Projects. The possible values are:
* stored locally - Needs to get values from a database. TODO
*/
int mProject = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_vote_main_admin);
// Find the view pager that will allow the user to swipe between fragments
ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
// Create an adapter that knows which fragment should be shown on each page
AdminFragmentPagerAdapter adapter = new AdminFragmentPagerAdapter(getSupportFragmentManager());
// Set the adapter onto the view pager
viewPager.setAdapter(adapter);
// initiate a rating bar
rBar = findViewById(R.id.rating_bar);
//float vote = rBar.getRating();
// Find all relevant views for user input
mResults = findViewById(R.id.rating_bar);
mProjectSpinner = findViewById(R.id.spinner_project);
// Run getRating method to get rating number from a rating bar
//getRating();
// Initiate button
mBtn = findViewById(R.id.voteButton);
// perform click event on button
mBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// get values and then displayed in a toast
//String totalStars = "Total Stars:: " + RatingBar.getNumStars();
float vote = rBar.getRating();
String rating = "Rating : " + vote;
Toast.makeText(getApplicationContext(), rating + "\n", Toast.LENGTH_LONG).show();
}
});
projectSpinner();
}
// Setup the dropdown spinner that allows the user to select the role.
private void projectSpinner() {
// Create adapter for spinner. The list options are from the String array it will use
// the spinner will use the default layout
ArrayAdapter projectSpinnerAdapter = ArrayAdapter.createFromResource(this,
R.array.projects, android.R.layout.simple_spinner_item);
// Specify dropdown layout style - simple list view with 1 item per line
projectSpinnerAdapter.setDropDownViewResource(android.R.layout.simple_dropdown_item_1line);
// Apply the adapter to the project spinner
mProjectSpinner.setAdapter(projectSpinnerAdapter);
// Set the integer mSelected to the constant values
mProjectSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String selection = (String) parent.getItemAtPosition(position);
if(mProjectSpinner.getSelectedItem() == "This is Hint Text");
if (!TextUtils.isEmpty(selection)) {
if (selection.equals(getString(R.string.nextGEMS1_5))) {
mProject = 0 ;
return;
} else if (selection.equals(getString(R.string.nextGEMS1_6))) {
mProject = 1;
return;
} else if (selection.equals(getString(R.string.nextGEMS1_7))) {
mProject = 2;
return;
} else if (selection.equals(getString(R.string.nextGEMS1_8))) {
mProject = 3;
return;
} else if (selection.equals(getString(R.string.nextGEMS1_9))) {
mProject = 4;
return;
}
else mProject = 0;
}
}
// Because AdapterView is an abstract class, onNothingSelected must be defined
@Override
public void onNothingSelected(AdapterView<?> parent) {
mProject = 0; // User
}
});
}
}
...
activity_vote_main_admin.xml
...
<?xml version="1.0" encoding="utf-8"?>
<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">
<androidx.viewpager.widget.ViewPager
android:name="com.example.confidencevotefragmentrebuild.testFragment1"
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
...
activity_login.xml
...
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context=".LoginActivity"
tools:showIn="@layout/activity_login">
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#5fb0c9"
android:orientation="vertical"
android:scrollbarAlwaysDrawVerticalTrack="true">
<TextView
android:id="@+id/login_title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="16dp"
android:layout_marginTop="16dp"
android:gravity="center_horizontal"
android:text="LOGIN"
android:textColor="#fff"
android:textSize="20sp"
android:textStyle="bold" />
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="500dp"
android:background="#ffffff"
android:elevation="4dp"
android:orientation="vertical"
android:padding="20dp"
android:layout_below="@+id/login_title"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="80dp">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="450dp"
android:orientation="vertical"
android:paddingTop="30dp">
<com.google.android.material.textfield.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="70dp">
<EditText
android:id="@+id/editText"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:drawableLeft="@drawable/usericon"
android:hint="User Name"
android:inputType="textEmailAddress"
android:maxLines="1" />
</com.google.android.material.textfield.TextInputLayout>
<com.google.android.material.textfield.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<EditText
android:id="@+id/editText2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="16dp"
android:drawableLeft="@drawable/lock"
android:hint="Password"
android:inputType="textPassword"
android:maxLines="1" />
</com.google.android.material.textfield.TextInputLayout>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right"
android:paddingTop="5dp"
android:text="Forgot Password?" />
<Button
android:id="@+id/submit_button"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="22dp"
android:background="@drawable/action_buttom"
android:text="Sign in"
android:textAllCaps="false"
android:textColor="#fff"
android:textSize="18sp" />
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="20dp"
android:orientation="horizontal"
android:paddingTop="1dp">
<TextView
android:id="@+id/attempts_text"
android:layout_width="wrap_content"
android:layout_height="25dp"
android:layout_gravity="center_horizontal"
android:paddingTop="1dp"
android:text="Number of attempts remaining: " />
<TextView
android:id="@+id/textView_Attempts"
android:layout_width="match_parent"
android:layout_height="25dp"
android:layout_gravity="center_horizontal"
android:paddingTop="1dp"
android:text="5" />
</LinearLayout>
<TextView
android:id="@+id/lnkRegister"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="1dp"
android:gravity="center"
android:paddingTop="30dp"
android:text="Register here"
android:textColor="#5fb0c9"
android:textSize="16sp" />
</LinearLayout>
</RelativeLayout>
<ImageButton
android:id="@+id/conferencevote_logo"
android:layout_width="210dp"
android:layout_height="180dp"
android:layout_below="@+id/login_title"
android:layout_centerHorizontal="true"
android:layout_marginTop="2dp"
android:elevation="4dp"
android:background="@drawable/rounded_button"
android:src="@drawable/confvotenew"
/>
</RelativeLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
...
AdminFragemntyPagerAdapter
...
package com.example.confidencevotefragmentrebuild;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
public class AdminFragmentPagerAdapter extends FragmentPagerAdapter {
public AdminFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
if (position == 0) {
return new testFragment1();
} else if (position == 1) {
return new testFragment2();
} else {
return new testFragment2();
}
}
@Override
public int getCount() {
return 3;
}
}
...
aactivity_vote_user.xml
...
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#5fb0c9"
android:orientation="vertical"
android:scrollbarAlwaysDrawVerticalTrack="true">
<TextView
android:id="@+id/vote_title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="16dp"
android:layout_marginTop="16dp"
android:gravity="center_horizontal"
android:text="USER VOTE"
android:textColor="#fff"
android:textSize="20sp"
android:textStyle="bold"/>
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="500dp"
android:background="#ffffff"
android:elevation="4dp"
android:orientation="vertical"
android:padding="20dp"
android:layout_below="@+id/vote_title"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginTop="80dp">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="450dp"
android:orientation="vertical"
android:paddingTop="70dp">
<com.google.android.material.textfield.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp">
<Spinner
android:id="@+id/spinner_project"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginTop="20dp"
android:layout_marginLeft="25dp"
android:layout_marginRight="25dp"
android:hint="@string/spinner_hint"
android:maxLines="1"
android:singleLine="true"
android:backgroundTint="@color/attCobalt"
android:popupBackground="@color/myBlue"
android:dropDownSelector="@color/attBlue"
/>
</com.google.android.material.textfield.TextInputLayout
>
<com.google.android.material.textfield.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
<RatingBar
android:id="@+id/rating_bar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:stepSize="1.0"
android:layout_marginTop="40dp"
android:theme="@style/rating_bar"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:paddingTop="5dp"
android:text="Vote and Submit" />
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</com.google.android.material.textfield.TextInputLayout>
<Button
android:id="@+id/voteButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="22dp"
android:background="@drawable/action_buttom"
android:text="Submit"
android:textAllCaps="false"
android:textColor="#fff"
android:textSize="18sp" />
/>
</LinearLayout>
<com.google.android.material.bottomnavigation.BottomNavigationView
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
<ImageButton
android:id="@+id/conferencevote_logo"
android:layout_width="210dp"
android:layout_height="180dp"
android:layout_below="@+id/login_title"
android:layout_centerHorizontal="true"
android:layout_marginTop="55dp"
android:elevation="4dp"
android:background="@drawable/rounded_button"
android:src="@drawable/confvotenew"
/>
</RelativeLayout>
...
My fragments are as follows.
...
package com.example.confidencevotefragmentrebuild;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
public class testFragment1 extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.activity_vote_user, container, false);
}
}
...
解决方案
这个问题有两个原因：
您没有在“activity_vote_main_admin.xml”上声明任何按钮，这就是为什么您的视图没有与活动绑定并给出空指针异常的原因。
可能是您在片段 xml 上声明按钮并尝试将其与活动绑定。
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