Dagger简单Demo

Dagger实现依赖注入，为了解决程序直接的耦合度。
本例子主要为了实现简单的依赖注入

配置：
Project级别的build.gradle

// 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:2.1.2'
        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
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

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

Module级别的build.gradle

apply plugin: 'com.android.application'
apply plugin: 'android-apt'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.android.demo"
        minSdkVersion 17
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.4.0'
    compile 'com.jakewharton:butterknife:8.0.1'
    apt 'com.jakewharton:butterknife-compiler:8.0.1'
    compile 'com.squareup.dagger:dagger:1.2.5'
    apt 'com.squareup.dagger:dagger-compiler:1.2.5'
}

布局

<RelativeLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <TextView
        android:id="@+id/message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />


    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/message"
        android:layout_margin="10dp"
        android:text="开始"/>
RelativeLayout>

Student.java

package com.android.demo;


/**
 * 学生
 */
public class Student {

    String id;
    String name;

    public void setId(String id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public Student(){}


}

AppModule.java

package com.android.demo;

import javax.inject.Singleton;

import dagger.Module;
import dagger.Provides;



@Module(injects = {MainActivity.class},complete = false ,library = true)
public class AppModule {

    @Provides @Singleton
    public Student provideStudent(){
        Student student = new Student();
        student.setId("2014");
        student.setName("WiseClown");
        return student;

    }
}

package com.android.demo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;


import javax.inject.Inject;

import butterknife.BindView;
import butterknife.ButterKnife;
import butterknife.OnClick;
import dagger.ObjectGraph;

public class MainActivity extends AppCompatActivity {

    @Inject
    Student student;

    @BindView(R.id.message)
    TextView message;

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

        ObjectGraph objectGraph = ObjectGraph.create(AppModule.class);
        objectGraph.inject(this);

        ButterKnife.bind(this);


    }

    @OnClick(R.id.btn)
    public void submit(View view){
       message.setText(student.getId()+"\n"+student.getName());
    }


}

分析：
在MainActivity中需要Student类的实例，所以通过依赖注入器将Student类在AppModule中实例化后再注入MainActivity中。