MVVM的使用_HelloWorld_dongjie_mvvm

网络 02-07 7768

使用DataBinding需要三个步骤：

1、启用DataBinding

?2、修改布局文件为DataBinding布局

把传统的布局替换为dataBinding布局：在外层布局按住Ctrl+回车会提示是否转化成dataBinding布局，直接转化：

?3、数据绑定：替换setContentView:?经过上述步骤，系统会自动生成ActivityMainBinding类，类名是布局文件名+Binding，布局文件首字母大写

<?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="account" type="com.example.myapplication.databinding.MyAccount" /> <variable name="activity" type="com.example.myapplication.MainActivity" /> </data> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity"> <TextView android:id="@+id/text_view" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@{account.name + '|' + account.level}" android:textSize="30dp" android:layout_gravity="center_horizontal" android:layout_marginTop="30dp" /> <Button android:id="@+id/bt" android:layout_width="150dp" android:layout_height="wrap_content" android:text="加1" android:textSize="20dp" android:layout_gravity="center_horizontal" android:onClick="@{activity.onClick}" android:layout_marginTop="40dp" /> </LinearLayout> </layout> public class MainActivity extends AppCompatActivity { ActivityMainBinding binding; MyAccount mAccount; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(R.layout.activity_main); binding = DataBindingUtil.setContentView(this, R.layout.activity_main); // binding.textView.setText("你好"); mAccount = new MyAccount(); mAccount.setLevel("1"); mAccount.setName("dongjie"); binding.setAccount(mAccount); binding.setActivity(this); } public void onClick(View v) { Toast.makeText(this, "点击", Toast.LENGTH_LONG).show(); // binding.setAccount(mAccount); // binding.textView.setText("aaaaa"); mAccount = new MyAccount(); mAccount.setLevel("2"); mAccount.setName("dongjiejie"); binding.setAccount(mAccount); } }

经过上述步骤，修改数据就可以自动更新到界面上了。

上面的方法还可以优化，当数据变化的时候，自动更新界面数据：

1、继承BaseObservable

2、get方法添加@Bindable

3、set方法添加notifyPropertyChanged(BR.name);

package com.example.myapplication.databinding; import androidx.databinding.BaseObservable; import androidx.databinding.Bindable; import com.example.myapplication.BR; public class MyAccount extends BaseObservable { String name; String level; @Bindable public String getName() { return name; } public void setName(String name) { this.name = name; // 当name发生变化的时候，更新界面数据, BR是DataBinding生成的，类似于R notifyPropertyChanged(BR.name); } @Bindable public String getLevel() { return level; } public void setLevel(String level) { this.level = level; notifyPropertyChanged(BR.level); } }

经过上述步骤，上面的onClick方法就可以这么写：改变数据源以后会自动同步到界面上

public void onClick(View v) { mAccount.setLevel("2"); mAccount.setName("dongjiejie"); }

到目前为止都是单向绑定，数据更新以后会直接同步到界面上，在@后面加等号就是双向绑定了，一般用的比较多得是输入框

MVVM实现需求需要以下几个步骤：

?下面给一个完整的demo：?

SecondActivity.java 和activity_second.xml

package com.example.myapplication.databinding2; import androidx.appcompat.app.AppCompatActivity; import androidx.databinding.DataBindingUtil; import android.os.Bundle; import com.example.myapplication.R; import com.example.myapplication.databinding.ActivitySecondBinding; public class SecondActivity extends AppCompatActivity { ActivitySecondBinding mBinding; MVVMViewModel mVVMViewModel; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mBinding = DataBindingUtil.setContentView(this, R.layout.activity_second); mVVMViewModel = new MVVMViewModel(getApplication(), mBinding); // 在xml里的变量都得初始化 mBinding.setViewModel(mVVMViewModel); } } <?xml version="1.0" encoding="utf-8"?> <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools"> <data>  <variable name="viewModel" type="com.example.myapplication.databinding2.MVVMViewModel" /> <variable name="activity" type="com.example.myapplication.MainActivity" /> </data> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity"> <EditText android:id="@+id/edit_view" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginLeft="30dp" android:layout_marginRight="30dp" android:textSize="30dp" android:text="@={viewModel.inputStr}" android:layout_marginTop="30dp" />  <Button android:id="@+id/bt" android:layout_width="150dp" android:layout_height="wrap_content" android:text="点击" android:textSize="20dp" android:layout_gravity="center_horizontal" android:onClick="@{viewModel.getData}" android:layout_marginTop="40dp" /> <TextView android:id="@+id/text_view" android:textSize="20dp" android:textColor="#000" android:layout_marginTop="30dp" android:layout_gravity="center_horizontal" android:layout_width="match_parent" android:text="@{viewModel.result}" android:layout_height="wrap_content"/> </LinearLayout> </layout>

MVVMViewModel.java

这一层相当于MVP的Presenter，处理逻辑，它里面调用Model层来请求数据，然后通过DataBinding来设置到界面上，如果遇到请求权限等操作，此层可以持有Activity的对象，或者用EventBus也可以，不过一般不要这么做，一般用LiveData+ViewModel的方式来做。

package com.example.myapplication.databinding2; import android.app.Application; import android.view.View; import androidx.databinding.BaseObservable; import androidx.databinding.Bindable; import com.example.myapplication.BR; import com.example.myapplication.databinding.ActivitySecondBinding; // MVVMViewModel相当于MVP的Presenter，处理业务逻辑 public class MVVMViewModel extends BaseObservable { Application application; ActivitySecondBinding mBinding; String result; String inputStr; MVVMModel mModel; public MVVMViewModel(Application application) { this.application = application; mModel = new MVVMModel(); } public MVVMViewModel(Application application, ActivitySecondBinding binding) { this(application); mBinding = binding; } public void getData(View v) { // String editStr = mBinding.editView.getText().toString(); // String ret = mModel.getScreenData(editStr); // setResult(ret); // 必须调用setResult才能更新 // 因为inputStr和控件是双向绑定，所以输入的时候inputStr是最新值，这样就不用传ActivitySecondBinding参数 String ret = mModel.getScreenData(inputStr); setResult(ret); } @Bindable public String getResult() { return result; } public void setResult(String result) { this.result = result; notifyPropertyChanged(BR.result); } @Bindable public String getInputStr() { return inputStr; } public void setInputStr(String inputStr) { this.inputStr = inputStr; notifyPropertyChanged(BR.inputStr); } }

MVVMModel.java? ? ?

这里模拟请求数据，一般是通过回调返回数据给MVVMViewModel的，这里为了简单写了同步方法

package com.example.myapplication.databinding2; import com.example.myapplication.databinding.ActivitySecondBinding; public class MVVMModel { public MVVMModel() { } public String getScreenData(String inputStr) { String str = "请求参数：" + inputStr + "\n请求数据：谢谢谢谢谢寻寻寻寻寻"; return str; } }