RecyclerView中使用CheckBox出现勾选混乱的解决方法
熟悉RecyclerView的人应该都知道,RecyclerView使用了复用机制,当在RecyclerView中得每一项都添加一个CheckBox时,勾选当前页面的几个CheckBox会发现下面还有其他的CheckBox也被勾选了,今天我们就来讨论一下如何解决这个问题。
首先当然是创建一个项目,然后在activity_main中添加一个RecyclerView控件,当然,在这之前,我们需要先添加RecyclerView的依赖,如下图:
然后 开始编辑activity_main:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <android.support.v7.widget.RecyclerView android:id="@+id/id_recycler_view" android:layout_width="match_parent" android:layout_height="match_parent"> </android.support.v7.widget.RecyclerView> </LinearLayout>
接下来为这个RecyclerView创建一个item布局文件,命名为item_recyclerview,并添加一个CheckBox空间,代码如下:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="60dp" android:gravity="center_vertical"> <CheckBox android:id="@+id/id_check_box" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginLeft="10dp" android:text="CheckBox"/> </LinearLayout>
接下来要编辑MainActivity了,包括从布局文件中找到刚才的RecyclerView控件,然后为其设置Adapter等,过程不再详细叙述,编辑后的代码如下:
public class MainActivity extends AppCompatActivity { private RecyclerView recyclerView; private MyAdapter myAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); recyclerView = (RecyclerView) findViewById(R.id.id_recycler_view); myAdapter = new MyAdapter(); recyclerView.setLayoutManager(new LinearLayoutManager(this)); recyclerView.setAdapter(myAdapter); } private class MyAdapter extends RecyclerView.Adapter { private List<String> content; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_recyclerview, parent, false); return new MyViewHolder(view); } @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) { MyViewHolder myViewHolder = (MyViewHolder) holder; myViewHolder.checkBox.setText(content.get(position)); } @Override public int getItemCount() { content = new ArrayList<>(); for (int i = 0; i < 100; i++) { content.add("CheckBox" + i); } return content.size(); } } private class MyViewHolder extends RecyclerView.ViewHolder { private CheckBox checkBox; public MyViewHolder(View itemView) { super(itemView); checkBox = (CheckBox) itemView.findViewById(R.id.id_check_box); } } }
可以看到,我们为这个RecyclerView设置了100个item,每个item里面都含有一个CheckBox,这时候运行这个应用,勾选出现的屏幕上的某一个或者多个CheckBox之后,当你向下拉的时候,问题出现了,你会发现下面会有很多的CheckBox也被选中了。下面我们就来着手解决这个问题,其实要解决也很简单,可以定义一个boolean类型的数组或者列表,用它来控制CheckBox的选中状态,当某个CheckBox被选中的时候将其选中状态记录在数组或列表中,当某个CheckBox滚动到屏幕上的时候,再用数组或列表中对应的值把它的选中状态改回来就好了,修改后的代码如下:
public class MainActivity extends AppCompatActivity { private RecyclerView recyclerView; private MyAdapter myAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); recyclerView = (RecyclerView) findViewById(R.id.id_recycler_view); myAdapter = new MyAdapter(); recyclerView.setLayoutManager(new LinearLayoutManager(this)); recyclerView.setAdapter(myAdapter); } private class MyAdapter extends RecyclerView.Adapter { private List<String> content; private boolean[] flag = new boolean[100];//此处添加一个boolean类型的数组 @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_recyclerview, parent, false); return new MyViewHolder(view); } @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) { MyViewHolder myViewHolder = (MyViewHolder) holder; myViewHolder.checkBox.setText(content.get(position)); myViewHolder.checkBox.setOnCheckedChangeListener(null);//先设置一次CheckBox的选中监听器,传入参数null myViewHolder.checkBox.setChecked(flag[position]);//用数组中的值设置CheckBox的选中状态 //再设置一次CheckBox的选中监听器,当CheckBox的选中状态发生改变时,把改变后的状态储存在数组中 myViewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { @Override public void onCheckedChanged(CompoundButton compoundButton, boolean b) { flag[position] = b; } }); } @Override public int getItemCount() { content = new ArrayList<>(); for (int i = 0; i < 100; i++) { content.add("CheckBox" + i); } return content.size(); } } private class MyViewHolder extends RecyclerView.ViewHolder { private CheckBox checkBox; public MyViewHolder(View itemView) { super(itemView); checkBox = (CheckBox) itemView.findViewById(R.id.id_check_box); } } }
比较这两段代码,我们会发现,首先我们定义了一个长度为100的数组,然后设置CheckBox的选中监听器,把null作为参数传进去,然后用数组中的值设置对应CheckBox的选中状态,最后再一次设置CheckBox的选中监听器,把CheckBox的选中状态储存在数组中的相应位置中。再次运行,发现问题已解决。
下面我们来讨论一下,如果要在RecyclerView的外面再添加一个CheckBox,用外面的CheckBox来控制RecyclerView中的CheckBox的全选和取消全选,要如何实现呢?
其实也很简单,只要用这个CheckBox来控制之前所定义的数组的指就好了。
首先来修改一下activity_main,代码如下:
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <LinearLayout android:layout_width="match_parent" android:layout_height="60dp" android:gravity="center_vertical"> <CheckBox android:id="@+id/id_select_all" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginLeft="10dp" android:text="SelectAll"/> </LinearLayout> <android.support.v7.widget.RecyclerView android:id="@+id/id_recycler_view" android:layout_width="match_parent" android:layout_height="match_parent"> </android.support.v7.widget.RecyclerView> </LinearLayout>
我们在RecyclerView的外面添加了一个CheckBox,用这个CheckBox来控制RecyclerView中的CheckBox的全选,接下来修改MainActivity:
public class MainActivity extends AppCompatActivity { private CheckBox selectAll; private RecyclerView recyclerView; private MyAdapter myAdapter; private boolean []flag;//把flag数组定义为全局变量 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); selectAll = (CheckBox) findViewById(R.id.id_select_all); recyclerView = (RecyclerView) findViewById(R.id.id_recycler_view); flag = new boolean[100];//初始化flag myAdapter = new MyAdapter(); recyclerView.setLayoutManager(new LinearLayoutManager(this)); recyclerView.setAdapter(myAdapter); //设置外面CheckBox的选中监听器,把它的选中状态赋值给其他的所有CheckBox,然后更新RecyclerView的Adapter selectAll.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { @Override public void onCheckedChanged(CompoundButton compoundButton, boolean b) { for (int i = 0; i < 100; i++) { flag[i] = b; } myAdapter.notifyDataSetChanged(); } }); } private class MyAdapter extends RecyclerView.Adapter { private List<String> content; // private boolean[] flag = new boolean[100]; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_recyclerview, parent, false); return new MyViewHolder(view); } @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) { MyViewHolder myViewHolder = (MyViewHolder) holder; myViewHolder.checkBox.setText(content.get(position)); myViewHolder.checkBox.setOnCheckedChangeListener(null); myViewHolder.checkBox.setChecked(flag[position]); myViewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { @Override public void onCheckedChanged(CompoundButton compoundButton, boolean b) { flag[position] = b; } }); } @Override public int getItemCount() { content = new ArrayList<>(); for (int i = 0; i < 100; i++) { content.add("CheckBox" + i); } return content.size(); } } private class MyViewHolder extends RecyclerView.ViewHolder { private CheckBox checkBox; public MyViewHolder(View itemView) { super(itemView); checkBox = (CheckBox) itemView.findViewById(R.id.id_check_box); } } }
这里我们先把记录CheckBox选中状态的数组定义为全局变量,然后设置外面的CheckBox的监听器,把它的选中状态赋值给其他的所有CheckBox,紧接着更新一下RecyclerView的Adapter就可以了
这里我们在讨论一下RecyclerView的另外一个问题,就是当要删除某个子项的时候会出现删除紊乱的情况,为了说明这个问题,我们
先来尝试实践一下,修改item_recyclerview:
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="60dp" android:gravity="center_vertical"> <CheckBox android:id="@+id/id_check_box" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginLeft="10dp" android:text="CheckBox"/> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentRight="true" android:layout_marginRight="10dp" android:text="delete"/> </RelativeLayout>
我们增加了一个Button,接下来设置这个Button,当它被点击的时候就删除它所在位置的item,修改MainActivity如下,主要修改的是Adapter部分,其他部分的代码就不贴了:
private class MyAdapter extends RecyclerView.Adapter { // private List<String> content; // private boolean[] flag = new boolean[100]; @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_recyclerview, parent, false); return new MyViewHolder(view); } @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) { final MyViewHolder myViewHolder = (MyViewHolder) holder; myViewHolder.checkBox.setText(content.get(position)); myViewHolder.checkBox.setOnCheckedChangeListener(null); myViewHolder.checkBox.setChecked(flag[position]); myViewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() { @Override public void onCheckedChanged(CompoundButton compoundButton, boolean b) { flag[position] = b; } }); //设置监听器,当按钮被点击是,删除它所在的item myViewHolder.button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { content.remove(position); notifyItemRemoved(position); } }); } @Override public int getItemCount() { // content = new ArrayList<>(); // for (int i = 0; i < 100; i++) { // content.add("CheckBox" + i); // } return content.size(); } } private class MyViewHolder extends RecyclerView.ViewHolder { private CheckBox checkBox; private Button button;//定义删除按钮 public MyViewHolder(View itemView) { super(itemView); checkBox = (CheckBox) itemView.findViewById(R.id.id_check_box); button = (Button) itemView.findViewById(R.id.id_delete); } }
这是点击Button,我们会发现,问题出现了,第一次可以正常删除,第二次删除的item却是我们点击的Button所在的下一个item,后面的删除也会各种混乱,这是因为函数里面的传入的参数position,它是在进行onBind操作时确定的,在删除单项后,已经出现在画面里的项不会再有调用onBind机会,这样它保留的position一直是未进行删除操作前的postion值,对于尚未进入画面的单项来说,它会使用新的position值(好吧这段是抄的,其实我也不太懂啥意思),解决方法如下:
myViewHolder.button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { content.remove(position); notifyItemRemoved(position); notifyItemRangeChanged(position, content.size());//对于被删掉的位置及其后range大小范围内的view进行重新onBindViewHolder } });
只要加一行代码就好了,这行代码的作用就是对于被删掉的位置及其后range大小范围内的view进行重新onBindViewHolder
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