Question

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.kartiggessan.srmp1">

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".LoginActivity" />
    <activity android:name=".Admin" />
    <activity android:name=".Kemaskini" />
    <activity android:name=".Padam" />
    <activity android:name=".Papar" />
    <activity android:name=".Tambah" />
    <activity android:name=".Daftar"></activity>
</application>

这是Android Manifest文件

package com.example.kartiggessan.srmp1;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

Button btnpensyarah,btnadmin;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    btnpensyarah = (Button) findViewById(R.id.btnpensyarah);
    btnadmin = (Button) findViewById(R.id.btnadmin);

    btnpensyarah.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent pensyarah = new Intent(MainActivity.this,LoginActivity.class);
            startActivity(pensyarah);
        }
    });

    btnadmin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent admin = new Intent(MainActivity.this, Admin.class);
            startActivity(admin);
        }
    });
}

这是MainActivity.java

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.kartiggessan.srmp1.MainActivity">

    <Button
        android:text="admin"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnadmin"
        android:layout_alignParentBottom="true"
        android:layout_alignEnd="@+id/btnpensyarah" />

    <Button
        android:text="Pensyarah"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnpensyarah"
        android:layout_above="@+id/btnadmin"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="88dp" />
</RelativeLayout>

这是activity_main.xml。

10-08 10:22:56.739 7018-7018/com.example.kartiggessan.srmp1 E/AndroidRuntime: FATAL EXCEPTION: main
                                                                              Process: com.example.kartiggessan.srmp1, PID: 7018
                                                                              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kartiggessan.srmp1/com.example.kartiggessan.srmp1.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.example.kartiggessan.srmp1.Session.loggedin()' on a null object reference
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                  at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                  at android.os.Looper.loop(Looper.java:148)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.example.kartiggessan.srmp1.Session.loggedin()' on a null object reference
                                                                                  at com.example.kartiggessan.srmp1.LoginActivity.onCreate(LoginActivity.java:29)
                                                                                  at android.app.Activity.performCreate(Activity.java:6237)
                                                                                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                  at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                  at android.os.Looper.loop(Looper.java:148) 
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                                  at java.lang.reflect.Method.invoke(Native Method) 
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是创建的日志

public static final String TAG = DbHelper.class.getSimpleName();

如何更改此代码

package com.example.kartiggessan.srmp1;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class LoginActivity extends AppCompatActivity implements View.OnClickListener {
    private Button btnLogin,btnDaftar;
    private EditText etNamaPensyarah,etKatalaluan;
    private DbHelper db;
    private Session session;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);

        btnLogin = (Button)findViewById(R.id.btnLogin);
        btnDaftar = (Button)findViewById(R.id.btnDaftar);
        etNamaPensyarah = (EditText)findViewById(R.id.etNamaPensyarah);
        etKatalaluan = (EditText)findViewById(R.id.etKataLaluan);
        btnLogin.setOnClickListener(this);
        btnDaftar.setOnClickListener(this);

        if(session.loggedin()){
            startActivity(new Intent(LoginActivity.this,Menu.class));
            finish();
        }
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.btnLogin:
                Intent login = new Intent(LoginActivity.this, Menu.class);
                startActivity(login);
                break;
            case R.id.btnDaftar:
                Intent daftar = new Intent(LoginActivity.this, Daftar.class);
                startActivity(daftar);
                break;
            default:
        }
    }

    private void login(){
        String namapensyarah = etNamaPensyarah.getText().toString();
        String katalaluan = etKatalaluan.getText().toString();

        if(db.getUser(namapensyarah,katalaluan)) {
            session.setLoggedin(true);
            startActivity(new Intent(LoginActivity.this, Menu.class));
            finish();
        }else{
            Toast.makeText(getApplicationContext(), "Nama  pensyarah dan KataLaluan adalah Salah",Toast.LENGTH_SHORT).show();
        }
    }
    }

这是login.java

问题是，当我点击按钮pensyarah时，应用程序不幸停止了。请解决它并立即评论。你的评论非常适用。

Android Studio停止出现问题？

0 个答案: