Android DataBinding工作原理

朱雀 2023-07-25 06:28 107阅读 0赞

AndroidX提供的DataBinding可以实现数据与UI的双向绑定，对Android APP的开发提供很大灵活性，通过在Layout XML中提供数据与UI控件的映射关系，在Activity编程中只需要操作数据对象，UI界面就可以自动更新。

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上述过程都是DataBinding自动完成的，我们只要按照约定编程就可以实现。参照下面例程理解绑定过程。

## 例程一 ##

新建Android工程  
使用Android Studio开发工具创建工程，  
修改app模块中的build.gradle配置文件  
添加如下依赖和配置

dataBinding { 
            enabled = true
        }
    
        api 'android.arch.lifecycle:extensions:1.1.1'
        api 'com.squareup.retrofit2:retrofit:2.5.0'
        api 'com.squareup.retrofit2:converter-scalars:2.3.0'
        api 'com.squareup.retrofit2:converter-gson:2.4.0'
        api 'com.squareup.retrofit2:adapter-rxjava2:2.4.0'
        api 'io.reactivex.rxjava2:rxjava:2.1.16'
        api 'io.reactivex.rxjava2:rxandroid:2.0.2'
        api 'androidx.recyclerview:recyclerview:1.1.0'
        api 'com.github.bumptech.glide:glide:4.9.0'
        api 'com.android.support:design:29.0.0'
        api 'androidx.viewpager2:viewpager2:1.0.0'
        api 'com.google.android.material:material:1.1.0'
        implementation 'com.nostra13.universalimageloader:universal-image-loader:1.9.5'

完整的build.gradle文件内容

apply plugin: 'com.android.application'
    
    android { 
        compileSdkVersion 29
    
        dataBinding { 
            enabled = true
        }
    
        defaultConfig { 
            applicationId "com.hk.testapp"
            minSdkVersion 16
            targetSdkVersion 29
            versionCode 1
            versionName "1.0"
    
            testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        }
    
        buildTypes { 
            release { 
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
            }
        }
    
    }
    
    dependencies { 
        implementation fileTree(dir: 'libs', include: ['*.jar'])
    
        api 'android.arch.lifecycle:extensions:1.1.1'
        api 'com.squareup.retrofit2:retrofit:2.5.0'
        api 'com.squareup.retrofit2:converter-scalars:2.3.0'
        api 'com.squareup.retrofit2:converter-gson:2.4.0'
        api 'com.squareup.retrofit2:adapter-rxjava2:2.4.0'
        api 'io.reactivex.rxjava2:rxjava:2.1.16'
        api 'io.reactivex.rxjava2:rxandroid:2.0.2'
        api 'androidx.recyclerview:recyclerview:1.1.0'
        api 'com.github.bumptech.glide:glide:4.9.0'
        api 'com.android.support:design:29.0.0'
        api 'androidx.viewpager2:viewpager2:1.0.0'
        api 'com.google.android.material:material:1.1.0'
        implementation 'com.nostra13.universalimageloader:universal-image-loader:1.9.5'
    
        implementation 'androidx.appcompat:appcompat:1.1.0'
        implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
        testImplementation 'junit:junit:4.12'
        androidTestImplementation 'androidx.test.ext:junit:1.1.1'
        androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    }

创建MainActivity  
默认创建的Layout布局视图是androidx.coordinatorlayout.widget.CoordinatorLayout类型的，在此类型无法测试DataBinding例程，Google可能做了更多的封装，使用其他方式实现DataBinding，我们使用layout View

<?xml version="1.0" encoding="utf-8"?>
    <layout 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">
    
        <data>
            <variable name="course" type="com.hk.testapp.Course" />
        </data>
    
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:orientation="vertical">
    
            <TextView
                android:id="@+id/name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@{course.name}"
                android:textSize="24sp" />
    
            <TextView
                android:id="@+id/score"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text='@{course.score+""}'
                android:textSize="24sp" />
    
            <EditText
                android:id="@+id/teacher"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:ems="10"
                android:inputType="textPersonName"
                android:textSize="24sp"
                android:text="@{course.teacher}" />
    
        </LinearLayout>
    
        
    
    
    </layout>

定义一个数据对象com.hk.testapp.Course，并且将其属性绑定到UI控件上  
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Couse课程类

package com.hk.testapp;
    
    public class Course { 
        private String name = null;
        private Integer score = null;
        private String teacher = null;
    
        public Course(String name,Integer score,String teacher)
        { 
            this.name = name;
            this.score = score;
            this.teacher = teacher;
        }
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public Integer getScore() { 
            return score;
        }
    
        public void setScore(Integer score) { 
            this.score = score;
        }
    
        public String getTeacher() { 
            return teacher;
        }
    
        public void setTeacher(String teacher) { 
            this.teacher = teacher;
        }
    }

MainActivity类  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 2]

package com.hk.testapp;
    
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.databinding.DataBindingUtil;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.util.Log;
    
    import com.hk.testapp.databinding.ActivityMainBinding;
    
    public class MainActivity extends AppCompatActivity { 
        private ActivityMainBinding binding = null;
        private Course course = null;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            course = new Course("Math", 100,"ChenQX");
            binding.setCourse(course);
    
            after10seconds();
        }
    
        private void after10seconds() { 
            new Handler().postDelayed(new Runnable() { 
                @Override
                public void run() { 
                course = new Course("Chinese", 120,"陈岐祥");
                binding.setCourse(course);
                    Log.e("After10Seconds...",course.getTeacher());
                }
            }, 10000);
        }
    }

执行结果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 3]  
界面等待10秒钟后，对数据对象重新赋值，观察界面变化  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 4]  
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## 例程二 ##

在例程一中，重新赋值必须调用一次bind.setObject方法  
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我们在数据实体类上添加Binding注解方法，并且在set方法中通知观察者就不需要定义此方法。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 7]

package com.hk.testapp;
    
    import androidx.databinding.BaseObservable;
    import androidx.databinding.Bindable;
    
    public class Teacher extends BaseObservable { 
        private String name = null;
        private Integer age = null;
    
        public Teacher(String name,Integer age)
        { 
            this.name = name;
            this.age = age;
        }
    
        @Bindable
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
            notifyPropertyChanged(BR.name);
        }
    
        @Bindable
        public Integer getAge() { 
            return age;
        }
    
        public void setAge(Integer age) { 
            this.age = age;
            notifyPropertyChanged(BR.age);
        }
    }

Main2Activity

package com.hk.testapp;
    
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.databinding.DataBindingUtil;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.util.Log;
    
    import com.hk.testapp.databinding.ActivityMain2Binding;
    
    public class Main2Activity extends AppCompatActivity { 
        private ActivityMain2Binding binding = null;
        private Teacher teacher = null;
        private Teacher2 teacher2 = null;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main2);
    
            binding = DataBindingUtil.setContentView(this, R.layout.activity_main2);
            teacher = new Teacher("ChenQX", 40);
            binding.setTeacher(teacher);
    
            teacher2 = new Teacher2();
            teacher2.name.set("Chenqx2");
            teacher2.age.set(42);
            binding.setTeacher2(teacher2);
    
            after10seconds();
        }
    
        private void after10seconds() { 
            new Handler().postDelayed(new Runnable() { 
                @Override
                public void run() { 
                teacher.setName("陈岐祥");
    
                teacher2.name.set("陈岐祥2");
                Log.e("After10Seconds...",teacher.getName());
                }
            }, 10000);
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 8]  
例程二中数据类的另一种写法，代码更加简洁

package com.hk.testapp;
    
    import androidx.databinding.ObservableField;
    import androidx.databinding.ObservableInt;
    
    public class Teacher2 { 
        public final ObservableField<String> name = new ObservableField<>();
        public final ObservableInt age = new ObservableInt();
    }

## 例程三（绑定列表） ##

定义Layout View控件

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android">
        <data>
            <variable name="course" type="com.hk.testapp.Course"/>
        </data>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:orientation="horizontal">
    
            <TextView
                android:layout_width="150dp"
                android:layout_height="wrap_content"
                android:text="@{course.name}"
                android:textSize="24sp" />
    
            <TextView
                android:layout_width="150dp"
                android:layout_height="wrap_content"
                android:text="@{course.teacher}"
                android:textSize="24sp" />
    
            <TextView
                android:layout_width="150dp"
                android:layout_height="wrap_content"
                android:text='@{course.score+""}'
                android:textSize="24sp" />
        </LinearLayout>
    </layout>

定义RecyclerView控件

定义Adapter适配类

package com.hk.testapp;
    
    import android.view.LayoutInflater;
    import android.view.ViewGroup;
    
    import androidx.recyclerview.widget.RecyclerView;
    
    import com.hk.testapp.databinding.CourseItemBinding;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ListHolder>{ 
    
        private List<Course> courseList = new ArrayList<>();
    
        public ListAdapter(List<Course> courseList) { 
            this.courseList = courseList;
        }
    
        @Override
        public ListHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
            return ListHolder.create(LayoutInflater.from(parent.getContext()), parent);
        }
    
        @Override
        public void onBindViewHolder(ListHolder holder, int position) { 
            holder.bindTo(courseList.get(position));
        }
    
        @Override
        public int getItemCount() { 
            if (courseList == null)
                return 0;
            return courseList.size();
        }
    
        static class ListHolder extends RecyclerView.ViewHolder { 
            private CourseItemBinding binding;
    
            static ListHolder create(LayoutInflater inflater, ViewGroup parent) { 
                CourseItemBinding binding2 = CourseItemBinding.inflate(inflater, parent, false);
                return new ListHolder(binding2);
            }
    
            private ListHolder(CourseItemBinding binding) { 
                super(binding.getRoot());
                this.binding = binding;
            }
    
            public void bindTo(Course course) { 
                binding.setCourse(course);
                binding.executePendingBindings();
            }
    
        }
    }

定义Main3Activity

package com.hk.testapp;
    
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.recyclerview.widget.LinearLayoutManager;
    import androidx.recyclerview.widget.RecyclerView;
    
    import android.os.Bundle;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class Main3Activity extends AppCompatActivity { 
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main3);
    
            List<Course> data = new ArrayList<>();
            for (int i = 0; i < 100; i++) { 
                Course c = new Course("Android"+i,i,"Teacher"+i);
                data.add(c);
            }
            RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
            LinearLayoutManager layoutManager = new LinearLayoutManager(
                    this, LinearLayoutManager.VERTICAL, false);
            recyclerView.setLayoutManager(layoutManager);
            recyclerView.setAdapter(new ListAdapter(data));
        }
    }

RecyclerView 通过Adapter装载数据到UI层  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 9]

## 测试双向绑定 ##

将XML中的配置修改一下，即可实现双向绑定  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 10]  
Layout XML文件

<?xml version="1.0" encoding="utf-8"?>
    <layout 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">
    
        <data>
            <variable name="course" type="com.hk.testapp.Course" />
        </data>
    
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:orientation="vertical">
    
            <TextView
                android:id="@+id/name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@={course.name}"
                android:textSize="24sp" />
    
            <TextView
                android:id="@+id/score"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text='@={course.score+""}'
                android:textSize="24sp" />
    
            <EditText
                android:id="@+id/teacher"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:ems="10"
                android:inputType="textPersonName"
                android:textSize="24sp"
                android:text="@={course.name}" />
    
        </LinearLayout>
    
        
    
    
    </layout>

Course数据类

package com.hk.testapp;
    
    import androidx.databinding.BaseObservable;
    import androidx.databinding.Bindable;
    import androidx.databinding.ObservableField;
    import androidx.databinding.ObservableInt;
    
    public class Course  extends BaseObservable { 
        public final ObservableField<String> name = new ObservableField<>();
        public final ObservableInt score = new ObservableInt();
        public final ObservableField<String> teacher = new ObservableField<>();
    }

MainActivity

package com.hk.testapp;
    
    import androidx.appcompat.app.AppCompatActivity;
    import androidx.databinding.DataBindingUtil;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.util.Log;
    
    import com.hk.testapp.databinding.ActivityMainBinding;
    
    public class MainActivity extends AppCompatActivity { 
        private ActivityMainBinding binding = null;
        private Course course = null;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            course = new Course();
            course.name.set("Math");
            course.score.set(100);
            binding.setCourse(course);
    
            //after10seconds();
        }
    
        private void after10seconds() { 
            new Handler().postDelayed(new Runnable() { 
                @Override
                public void run() { 
                // = new Course("Chinese", 120,"陈岐祥");
                //binding.setCourse(course);
                }
            }, 10000);
        }
    }

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代码下载  
链接：https://pan.baidu.com/s/1Inn8P\_\_qmjr0a06MTdnVZQ  
提取码：wxpj

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