Java 尝试对空对象引用、无线组调用虚方法

我添加了这个单选组，带有单选按钮，尽管现在我发现我的整个单选组都是空的？一件非常有趣的事情是，当我在API为22的设备上运行时，我的应用程序没有检测到这个错误，但是当我在28API模拟器上重新运行它时，这个错误确实出现了。 代码如下：

radioGroup = findViewById(R.id.radioGroup2);
    Rd1= findViewById(R.id.radioButton5);
    Rd2= findViewById(R.id.radioButton6);
    radioGroup.setOnCheckedChangeListener( new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            if (Rd1.isChecked()) {
                attemptLogin();
                Intent intent = new Intent(LoginActivity.this, BottomActivity.class);
                startActivity(intent);
            }else {
                if(Rd2.isChecked()) {
                    attemptLogin();
                    Intent intent = new Intent(LoginActivity.this, LoginActivity2.class);
                    startActivity(intent);
                }
            }

        }
    } );

这是XML代码，我已经尝试将RadioGroup视图添加到我的登录活动中，以便将两个按钮放置在彼此的上方，尽管一旦这样做，我立即出现了此错误

<RadioGroup
            android:id="@+id/radioGroup2"
            android:layout_width="361dp"
            android:layout_height="125dp"
            android:layout_gravity="bottom"
            android:background="@color/licolor"
            android:gravity="center"
            android:layout_marginTop="20dp"
            android:orientation="vertical"
            tools:ignore="UselessParent">

            <RadioButton
                android:id="@+id/radioButton5"
                android:layout_width="match_parent"
                android:layout_height="45dp"
                android:layout_marginTop="16dp"
                android:background="@drawable/mybutton"
                android:gravity="center"
                android:text="@string/register"
                android:textColor="#fafafa"
                android:textStyle="bold"
                android:textSize="19sp"
                android:button="@null"/>

            <RadioButton
                android:id="@+id/radioButton6"
                android:layout_width="match_parent"
                android:layout_height="45dp"
                android:layout_marginTop="16dp"
                android:background="@drawable/mybutton"
                android:gravity="center"
                android:text="@string/login"
                android:textColor="#fafafa"
                android:textStyle="bold"
                android:textSize="19sp"
                android:button="@null"/>

        </RadioGroup>

这是gradle文件：

apply plugin: 'com.android.application'

android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.example.shrinkio"
    minSdkVersion 19
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner 
"android.support.test.runner.AndroidJUnitRunner"
    vectorDrawables.useSupportLibrary = true
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

}

}

---

您的RadioGroup具有id=“RadioGroup 2”

在代码中，您尝试查找“radioGroup”

只需将其更改为：

radioGroup = findViewById( R.id.radioGroup2 );

---

它显示空指针异常。检查它所指的线，找出空对象。@Ravi我不明白它说什么，你能帮忙吗？看起来它找不到你的广播组。检查您是否已使用正确的id@Ravi我有一个人，在XML上，射线组的名称是“射线组2”，它对应于Java的名称，请检查您的代码。您已发布为“radioGroup=findViewById（R.id.radioGroup）；”。它在XML和活动中应该是相同的。您可以重新执行活动吗，所以我希望单击单选按钮并开始一个新的活动activity@TomasMota更新的代码显示单击的按钮。你可以在识别点击时执行startActivity（）。我尝试过，尽管，它仍然显示相同的错误，有什么建议吗？我尝试过，尽管，它仍然显示相同的错误，有什么建议吗？此外，每当我在较低的API设备上运行应用程序时，它运行得非常好，只有在22 API或更高的设备上运行时，才会出现此错误。

RadioGroup radioGroup;
RadioButton RD1;
RadioButton RD2;
RadioButton RD3;

    radioGroup = (RadioGroup)findViewById(R.id.radioGroup);
    RD1 = (RadioButton)findViewById(R.id.radioButton1);
    RD2 = (RadioButton)findViewById(R.id.radioButton2);
    RD3 = (RadioButton)findViewById(R.id.radioButton3);

           radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup radioGroup, int checkedButtonId) {

            // This will get the radiobutton that has changed in its check state
            RadioButton checkedRadioButton = (RadioButton)radioGroup.findViewById(checkedButtonId);
            // This puts the value (true/false) into the variable
            boolean isChecked = checkedRadioButton.isChecked();
            // If the radiobutton that has changed in check state is now checked...
            if (isChecked)
            {
                switch (checkedButtonId)
                {
                    case R.id.radioButton1:
                        Log.i("test" , "Checked Button 1 ");
                        break;
                    case R.id.radioButton2:
                        Log.i("test" , "Checked Button 2 ");
                        break;
                    case R.id.radioButton3:
                        Log.i("test" , "Checked Button 3 ");
                        break;

                }
            }

        }
    });

apply plugin: 'com.android.application'

android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.example.shrinkio"
    minSdkVersion 19
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner 
"android.support.test.runner.AndroidJUnitRunner"
    vectorDrawables.useSupportLibrary = true
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
    }
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:28.0.0'
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
implementation 'com.android.support:design:28.0.0'
implementation 'com.android.support:support-vector-drawable:28.0.0'
implementation 'com.android.support:support-v4:28.0.0'
implementation 'com.android.support:recyclerview-v7:28.0.0'
implementation 'android.arch.lifecycle:extensions:1.1.1'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.google.firebase:firebase-core:16.0.7'
implementation 'com.google.firebase:firebase-auth:16.1.0'
implementation "com.google.android.gms:play-services-gcm:16.1.0"
implementation 'com.android.support:cardview-v7:28.0.0'

apply plugin: 'com.google.gms.google-services'

android:id="@+id/radioGroup2"

radioGroup = findViewById( R.id.radioGroup );

radioGroup = findViewById( R.id.radioGroup2 );