java - 与 OnCreate() 一起使用的方法来更新 Activity ？

Question

我有一个 android studio Activity ，其中包含 RecyclerView、适配器和 Activity 底部的一个不可见按钮。 RecyclerView 内的每个 itemView 也有一个 CheckBox。在我的适配器类中，我初始化了复选框，并具有类似 - if checkbox.isChecked - then make public static int num = 1 else num = 2; 的内容；然后，这个静态变量被发送到我的 Activity_main，其中我需要变得可见的底部按钮可以使用 if 语句可见 - if Adapter.num == 1 then button.MakeVisible(true);

问题是它在我的 Oncreate 中，只有在 Activity 完成后才会被调用。静态号码发送没有问题，但 Activity 不会更新以实际显示这一点。我必须重新启动 Activity 才能使按钮真正可见。

适配器类

public static int p = 0;
 @Override
    public void onBindViewHolder(@NonNull final Adapter.CustomViewHolder holder, 
  final int position) {

                    addedCars = new ArrayList<>();

                    holder.car.setText(mCars.get(position).getCarName());






                    holder.mCheckBox.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            if(holder.mCheckBox.isChecked()){
                                Log.d("tag1", "checked");

                                addedCars.add(mCars.get(position));
                                String x = Integer.toString(addedCars.size());
                                Log.d("tag1", x );

                                p = 1;



                                holder.mButton2.setOnClickListener(new View.OnClickListener() {
                                    @Override
                                    public void onClick(View view) {

                                    }
                                });



            }
            else {
                Log.d("tag1", "unchecked");
                addedCars.remove(mCars.get(position));

                p = 2;

            }
        }

    });



}

Activity_Main类

 public class MainActivity extends AppCompatActivity {

RecyclerView mRecyclerView;
Adapter mAdapter;
RecyclerView.LayoutManager mLayoutManager;




Button mButton;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mRecyclerView = findViewById(R.id.RecyclerView);

    mButton = findViewById(R.id.button);





    ArrayList<Car> cars = new ArrayList<>();

    cars.add(new Car("Toyota"));
    cars.add(new Car("Ford"));
    cars.add(new Car("Tesla"));

    mAdapter = new Adapter(cars);
    mRecyclerView.setAdapter(mAdapter);
    mLayoutManager = new LinearLayoutManager(this);
    mRecyclerView.setLayoutManager(mLayoutManager);
    mRecyclerView.setHasFixedSize(true);



   if (mAdapter.p == 1){
       mButton.setVisibility(View.VISIBLE);
   }








       }


  }

Answer 1

如果您想将 num p 从 RecyclerView Adapter 发送到 Activity，您需要一个接口(interface)来执行以下步骤:

已经在android中测试了我的代码希望这对你有用

1. 在适配器中创建接口(interface)

       // create an instance of OnItemChangeListener 
       public OnItemChangeListener onItemChangeListener;
   
       public interface OnItemChangeListener {
            void onItemChanged(int p);
        }
   
        //set the instance of onItemChangeListener from the main activity
        public void setOnItemChangeListener(OnItemChangeListener onItemChangeListener) {
               this.onItemChangeListener = onItemChangeListener;
        }
   
         holder.mCheckBox.setOnClickListener(new View.OnClickListener() {
                   @Override
                   public void onClick(View view) {
                       if(holder.mCheckBox.isChecked()){
                           Log.d("tag1", "checked");
   
                           addedCars.add(mCars.get(position));
                           String x = Integer.toString(addedCars.size());
                           Log.d("tag1", x );
   
                           p = 1;
                           /*
                            * notify updated value using call back 
                            */
   
                            onItemChangeListener.onItemChanged(p);
   
   
   
                           holder.mButton2.setOnClickListener(new View.OnClickListener() {
                               @Override
                               public void onClick(View view) {
   
                               }
                           });
   
   
   
       }
   

2最终通知主activity更新

mAdapter = new Adapter(cars);

mAdapter.setOnItemChangeListener(new /*your adapter name */.OnItemChangeListener() {
        @Override
        public void onItemChanged(int p) {
            // here you will get the latest updated value of p 
            // now you can update you view accordingly
        }
});



mRecyclerView.setAdapter(mAdapter);
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setHasFixedSize(true);