java - 如何修复此 DataBinding 和 LiveData 代码？

Question

我正在尝试将 DataBinding 与 LiveData 连接，但遇到了一些问题，我不知道如何修复。我不确定 LifecycleOwner 是否做错了什么，但它不起作用。还值得赞赏的是为什么正确的方法是正确的一些解释。该应用程序甚至没有启动，我不知道我的错误是什么。感谢您的帮助

package com.example.teststuff;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.databinding.Observable;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.example.teststuff.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {

    ActivityMainBinding binding;
    MainActivityViewModel model;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        model = ViewModelProviders.of(this).get(MainActivityViewModel.class);
        binding.setViewmodel(model);
        model.setText("Hello");
        binding.setLifecycleOwner(this);

    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>
        <variable name="viewmodel" type="com.example.teststuff.MainActivityViewModel" />
    </data>

    <RelativeLayout 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"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <EditText
            android:text="@{viewmodel.text}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </RelativeLayout>
</layout>

package com.example.teststuff;

import android.widget.Button;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MainActivityViewModel extends ViewModel {

    private MutableLiveData<String> text;

    public MutableLiveData<String> getText() {
        return text;
    }

    public void setText(String text) {
        this.text.setValue(text);
    }
}

Answer 1

您的代码通常是正确的。

您需要确保 build.gradle 中有以下行:

android {
    ...
    dataBinding {
        enabled = true
    }
}

dependencies {
    ...
    implementation 'androidx.lifecycle:lifecycle-extensions:2.0.0'
}

代码的更正版本

package com.example.teststuff;

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

import android.os.Bundle;

import com.example.teststuff.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {

    ActivityMainBinding binding;
    MainActivityViewModel model;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        model = ViewModelProviders.of(this).get(MainActivityViewModel.class);
        binding.setViewmodel(model);
        model.setText("Hello");
        binding.setLifecycleOwner(this);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>
        <variable name="viewmodel" type="com.example.teststuff.MainActivityViewModel" />
    </data>

    <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"
        tools:context=".MainActivity">

        <EditText
            android:text="@{viewmodel.text}"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </RelativeLayout>
</layout>

package com.example.teststuff;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MainActivityViewModel extends ViewModel {

    private MutableLiveData<String> text = new MutableLiveData<>();

    public MutableLiveData<String> getText() {
        return text;
    }

    public void setText(String text) {
        this.text.setValue(text);
    }
}