Question

我正在学习Butterknife，这是我的简单示例代码。但是当我跑步时，它会在{strong>“NullPointerException”中抛出setText。是我在很多论坛上读过的Android工作室错误，还是编码错误

public class MainActivity extends AppCompatActivity {

    @Inject
    SharedPreferences mSharedPrefs;
    @BindView(R.id.txtName) EditText entervalue;
    @BindView(R.id.enternamelabel) TextView enternamelabel;

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

        //Call Butterknife
        ButterKnife.bind(MainActivity.this);

        enternamelabel.setText("Enter Name");

        //((DemoApplication) getApplication()).getComponent().inject(this);
        //mSharedPrefs.edit().putString("status", "success!").apply();

    }

应用模块

apply plugin: 'com.android.application'
apply plugin: 'com.neenbedankt.android-apt'   //For Butterknife

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.3"
    defaultConfig {
        applicationId "com.myandroidframework.myandroidframework"
        minSdkVersion 15
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        compileOptions.incremental = false
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'

    // Dependency Injection - Dagger2
    compile 'com.google.dagger:dagger:2.0'
    provided 'com.google.dagger:dagger-compiler:2.0'
    provided 'org.glassfish:javax.annotation:10.0-b28'

    // Dependency Injection - Butterknife
    testCompile 'junit:junit:4.12'
    compile 'com.jakewharton:butterknife:8.5.1'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.5.1'
}

项目模块

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.2'
        //For Butterknife
        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'

    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

错误：

07-19 16:11:22.422 21754-21754/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                   Process: com.myandroidframework.myandroidframework, PID: 21754
                                                   java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myandroidframework.myandroidframework/com.myandroidframework.myandroidframework.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                       at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                       at android.os.Handler.dispatchMessage(Handler.java:102)
                                                       at android.os.Looper.loop(Looper.java:154)
                                                       at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                                                       at com.myandroidframework.myandroidframework.MainActivity.onCreate(MainActivity.java:37)
                                                       at android.app.Activity.performCreate(Activity.java:6679)
                                                       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) 
                                                       at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) 
                                                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                       at android.os.Looper.loop(Looper.java:154) 
                                                       at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                       at java.lang.reflect.Method.invoke(Native Method) 
                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

以下是问题

我不需要添加此行

apply plugin: 'com.jakewharton.butterknife'

以下将是我的应用级别gradle

// Dependency Injection - Butterknife
    testCompile 'junit:junit:4.12'
    compile 'com.jakewharton:butterknife:8.5.1'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.5.1'
}

下面是我的项目级别gradle

dependencies {
        classpath 'com.android.tools.build:gradle:2.3.2'
        //For Butterknife
        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'

    }

Answer 2

App Level（build.gradle）

apply plugin: 'android-apt'
dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:24.2.1'
    testCompile 'junit:junit:4.12'
    compile 'com.jakewharton:butterknife:8.4.0'
    apt 'com.jakewharton:butterknife-compiler:8.4.0'
}


Project Level(build.gradle)

buildscript {
    repositories {
        jcenter()
    }
    dependencies {

        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

Butterknife - 空指针异常

2 个答案: