Android 上的简单 MVVM 架构，Java 上的 AndroidX

Question

我真的很生气，想弄清楚这个混蛋是如何创建一个简单的 MVVM 模式的 Android activity.

我想要的只是将视图模型 public 方法（打印 "Eureka!" 日志）绑定到按钮（带有 onClick 操作）。

为了实现这一点，我现在所做的是：

data_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context="it.XXXXX.XXXXX.ui.data.DataActivity"
    >

    <data>
        <variable
            name="viewModel"
            type="it.XXXXX.XXXXX.ui.data.DataViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical">

            <TextView
                android:id="@+id/some_useless_id_1"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:gravity="center_horizontal"
                android:textAppearance="@style/TextAppearance.AppCompat.Body1"
                tools:text="Press this beautiful button ;)" />

            <Button
                android:id="@+id/some_useless_id_2"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:onClick="@{() -> viewModel.test()}"
                android:text="@string/button" />
        </LinearLayout>
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

DataViewModel.java

package it.XXXXX.XXXXX.ui.data;

import android.util.Log;

import androidx.lifecycle.ViewModel;

public class DataViewModel extends ViewModel {
    public void test() {
        Log.d("test", "EUREKA!");
    }
}

DataActivity.java

package it.XXXXX.XXXXX.ui.data;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;

import it.XXXXX.XXXXX.R;

public class DataActivity extends AppCompatActivity {

    private DataViewModel mViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.data_activity);
        this.mViewModel = new ViewModelProvider(this).get(DataViewModel.class);
    }
}

...最后（因为我正在处理现有的应用程序）我调用视图：

...
        ((Button)this.findViewById(R.id.btnDataSync2)).setOnClickListener(new OnClickListener(){
            public void onClick(View arg0) {
                Intent i = new Intent(MainActivity.this, DataActivity.class);
                MainActivity.this.startActivity(i);
            }
        });
...

预期的行为是通过按下 DataView（已加载）来读取日志，但没有任何反应（按钮按下动画除外）。

有人知道问题出在哪里吗？
提前致谢！

Answer 1

Step to enable data binding in an Android app:

add android.databinding.enableV2=true in your "gradle.properties" file;
add dataBinding { enabled = true } in the app "build.gradle" file, in the android section:

android {
    compileSdkVersion 28

    ...

    dataBinding {
        enabled = true
    }
}

运行 a gradle sync and build in Android Studio.

Update

I forgot to tell you have to modify your onCreate method like this:

package it.XXXXX.XXXXX.ui.data;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;

import android.os.Bundle;

import it.XXXXX.XXXXX.R;
import it.XXXXX.XXXXX.databinding.DataActivityBinding;

public class DataActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        DataViewModel mViewModel = new DataViewModel();

        DataActivityBinding binding = DataBindingUtil.setContentView(this, R.layout.data_activity);
        binding.setViewModel(mViewModel);
    }
}

Answer 2

我认为我没有正确绑定 Activity 中的 ViewModel:

DataActivity.java

public class DataActivity extends AppCompatActivity {

    private DataViewModel mViewModel;
    private DataActivityBinding mBinding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        this.mViewModel = new DataViewModel();
        this.mBinding = DataBindingUtil.setContentView(this, R.layout.data_activity);
        this.mBinding.setViewModel(this.mViewModel);
    }
}

希望这对某人有所帮助。

Ps。感谢 @medaip90 的有用建议！

Android 上的简单 MVVM 架构，Java 上的 AndroidX

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