LiveData 是将数据和UI分离。将数据独立到一个ViewModel里面
ViewModelTest类
定义了一个变量item
package com.example.viewmodel02;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;
public class ViewModelTest extends ViewModel {
private MutableLiveData<Integer> item;
public MutableLiveData<Integer> getItem() {
if(this.item == null){
this.item = new MutableLiveData<>();
this.item.setValue(0);
}
return item;
}
public void addItem(int n){
this.item.setValue(this.item.getValue()+n);
}
}
在activity_mian中就可以调用这个类来使用item变量
通过设置一个Observe来查看item的改变,然后改变textview里面的值
package com.example.viewmodel02;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
public class MainActivity extends AppCompatActivity {
ViewModelTest viewModelTest;
TextView textView;
ImageButton buttonlike;
ImageButton buttondislike;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
int textnumber = R.id.text00;
int buttonnumber = R.id.button1;
int buttonnumber2 = R.id.button2;
textView = findViewById(textnumber);
buttonlike = findViewById(buttonnumber);
buttondislike = findViewById(buttonnumber2);
viewModelTest = ViewModelProviders.of(this).get(ViewModelTest.class);
viewModelTest.getItem().observe(this, new Observer<Integer>() {
@Override
public void onChanged(Integer integer) {
textView.setText(String.valueOf(integer));
}
});
buttonlike.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
viewModelTest.addItem(1);
}
});
buttondislike.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
viewModelTest.addItem(-1);
}
});
}
}
layout
点击红心+1 点击空心-1
测试结果