介绍

今天的课程会比较好玩，我们在之前的Service篇章中看到了一种putExtras和getExtras来进行activity与service间的传值。而恰恰这种传值其实也是Android里的通用传值法。它同样可以适用在activity与activity间传值。

Android中的传值

传单个值

传多个值

 

具体我们来结合例子来看吧

课程目标

正向传值到下一个activity上

反向传值到调用activity上

• 正向传值用：Intent+Bundle传值；
• 反向传值我们使用：registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {回调，并判断这个result.getResultCode()；
• 同时，我们制作了一个ActivityCollector extends Application来注册所有打开的activity，然后通过这个控制类来实现一键关闭所有打开的activity；

来看代码实现吧

全代码

前端

表格控制中用到的item_list.xml
 

<?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="match_parent"
    android:padding="5dp">

    <ImageView
        android:id="@+id/iconImg"
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:layout_centerInParent="true"
        android:src="@drawable/icon_1_128"
        />

    <TextView
        android:id="@+id/iconText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/iconImg"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="30dp"
        android:text="text"
        android:textSize="18sp"
        />

</RelativeLayout>

表格控制用到的GenericAdapter（这个在我们之前讲Adapter的篇章中已经写过）

package org.mk.android.demo;

import android.content.Context;
import android.util.Log;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public abstract class
GenericAdapter <T> extends BaseAdapter {
    private List<T> data;
    private int layoutRes;

    public GenericAdapter() {
    }

    public GenericAdapter(List<T> data, int layoutRes) {
        this.data = data;
        this.layoutRes = layoutRes;
    }

    @Override
    public int getCount() {
        Log.i("app",">>>>>>data.size: "+data.size());
        if(data!=null) {
            return data.size();
        }
        return 0;
    }

    @Override
    public T getItem(int position) {
        return data.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Log.i("app",">>>>>>into getView");
        ViewHolder holder = ViewHolder.bind(parent.getContext(), convertView, parent, layoutRes
                , position);
        bindView(holder, getItem(position));
        return holder.getItemView();
    }

    //添加一个元素
    public void add(T item) {
        if (data == null) {
            data = new ArrayList<>();
        }
        data.add(item);
        notifyDataSetChanged();
    }

    //往特定位置，添加一个元素
    public void add(int position,T item){
        if (data == null) {
            data = new ArrayList<>();
        }
        data.add(position, item);
        notifyDataSetChanged();
    }

    public void remove(T item) {
        if(data != null) {
            data.remove(item);
        }
        notifyDataSetChanged();
    }

    public void remove(int position) {
        if(data != null) {
            data.remove(position);
        }
        notifyDataSetChanged();
    }

    public void clear() {
        if(data != null) {
            data.clear();
        }
        notifyDataSetChanged();
    }

    public abstract void bindView(ViewHolder holder, T obj);

    public static class ViewHolder {

        private SparseArray<View> mViews;   //存储ListView 的 item中的View
        private View item;                  //存放convertView
        private int position;               //游标
        private Context context;            //Context上下文

        //构造方法，完成相关初始化
        private ViewHolder(Context context, ViewGroup parent, int layoutRes) {
            mViews = new SparseArray<>();
            this.context = context;
            View convertView = LayoutInflater.from(context).inflate(layoutRes, parent,false);
            convertView.setTag(this);
            item = convertView;
        }
        public static ViewHolder bind(Context context, View convertView, ViewGroup parent,
                                      int layoutRes, int position) {
            ViewHolder holder;
            if(convertView == null) {
                holder = new ViewHolder(context, parent, layoutRes);
            } else {
                holder = (ViewHolder) convertView.getTag();
                holder.item = convertView;
            }
            holder.position = position;
            return holder;
        }
        public <T extends View> T getView(int id) {
            T t = (T) mViews.get(id);
            if(t == null) {
                t = (T) item.findViewById(id);
                mViews.put(id, t);
            }
            return t;
        }
        /**
         * 获取当前条目
         */
        public View getItemView() {
            return item;
        }

        /**
         * 获取条目位置
         */
        public int getItemPosition() {
            return position;
        }

        /**
         * 设置文字
         */
        public ViewHolder setText(int id, CharSequence text) {
            View view = getView(id);
            if(view instanceof TextView) {
                ((TextView) view).setText(text);
            }
            return this;
        }

        /**
         * 设置图片
         */
        public ViewHolder setImageResource(int id, int drawableRes) {
            View view = getView(id);
            if(view instanceof ImageView) {
                ((ImageView) view).setImageResource(drawableRes);
            } else {
                view.setBackgroundResource(drawableRes);
            }
            return this;
        }

        /**
         * 设置标签
         */
        public ViewHolder setTag(int id, Object obj) {
            getView(id).setTag(obj);
            return this;
        }

        public ImageView iconImg;
        public TextView iconText;
    }
}

 activity_home_page.xml文件

• activity_main.xml文件里点击【注册】按钮跳到activity_home_page.xml文件。
• 然后把activity_main.xml文件中的内容显示在activity_home_page.xml的toast中。
• 在activity_home_page.xml文件中选择一个图标后返回activity_main.xml，并显示用户选择的内容；

<?xml version="1.0" encoding="utf-8"?>
<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"
    android:padding="5dp"
    tools:context=".HomePageActivity">
    <!--numColumns设置每行显示多少个-->
    <GridView
        android:id="@+id/gridPhoto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:numColumns="3" />
</RelativeLayout>

 activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <TableRow>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="请输入注册信息："
            android:textSize="18dp" />
    </TableRow>

    <TableRow>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="用户名："
            android:textSize="18dp" />

        <EditText
            android:id="@+id/edTextLoginName"
            android:layout_width="200dp"
            android:layout_height="wrap_content"
            android:inputType="text"
            android:text="" />
    </TableRow>

    <TableRow>

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center_vertical"
            android:text="性别："
            android:textSize="18dp" />

        <RadioGroup
            android:id="@+id/rgGroup"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="center_vertical"

            android:orientation="horizontal">

            <RadioButton
                android:id="@+id/radioMan"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:layout_marginRight="30dip"
                android:text="男性" />

            <RadioButton
                android:id="@+id/radioWoman"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="女性" />
        </RadioGroup>
    </TableRow>

    <TableRow>

        <Button
            android:id="@+id/buttonRegister"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_span="2"
            android:text="注册"
            android:textSize="18dp" />
    </TableRow>

    <TableRow>

        <ImageView
            android:id="@+id/selectedImg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_span="2" />
    </TableRow>
</TableLayout>

 后端代码

ActivityCollector

用于收集和一键关闭所有打开的Activity用

package org.mk.android.demo;

import android.app.Activity;
import android.app.Application;
import android.util.Log;

import java.util.LinkedList;
import java.util.List;

public class ActivityCollector extends Application {
    //运用list来保存们每一个activity是关键
    private List<Activity> mList = new LinkedList<Activity>();
    //为了实现每次使用该类时不创建新的对象而创建的静态对象
    private static ActivityCollector instance;

    //构造方法
    private ActivityCollector() {
    }

    //实例化一次
    public synchronized static ActivityCollector getInstance() {
        if (null == instance) {
            instance = new ActivityCollector();
        }
        return instance;
    }

    //addActivity
    public void addActivity(Activity activity) {
        mList.add(activity);
    }

    //removeOneActivity
    public void removeActivity(Activity activity) {
        mList.remove(activity);
    }

    //关闭每一个list内的activity
    public void exit() {
        try {
            if (mList != null && mList.size() > 0) {
                Log.i("app", ">>>>>>activity size->" + mList.size());
                for (Activity activity : mList) {
                    if (activity != null)
                        Log.i("app", ">>>>>>remove activity...");
                    activity.finish();
                }
            } else {
                Log.i("app", ">>>>>>there is no activity need to be closed!");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            System.exit(0);
        }
    }

    //杀进程
    public void onLowMemory() {
        super.onLowMemory();
        System.gc();
    }
}

 IconBean.java

package org.mk.android.demo;

import java.io.Serializable;

public class IconBean implements Serializable {
    public IconBean(int imgId, String iconText) {
        this.imgId = imgId;
        this.iconText = iconText;
    }

    private int imgId;
    private String iconText = "";

    public int getImgId() {
        return imgId;
    }

    public void setImgId(int imgId) {
        this.imgId = imgId;
    }

    public String getIconText() {
        return iconText;
    }

    public void setIconText(String iconText) {
        this.iconText = iconText;
    }
}

HomePageActivity.java

package org.mk.android.demo;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class HomePageActivity extends AppCompatActivity {

    private String loginName;
    private int gender;
    private Context ctx;
    private GridView gridPhoto;
    private BaseAdapter adapter = null;
    private List<IconBean> data = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home_page);
        ActivityCollector.getInstance().addActivity(this);
        Intent it = getIntent();
        Bundle bd = it.getExtras();
        loginName = bd.getString("loginName");
        gender = bd.getInt("gender");
        Toast.makeText(HomePageActivity.this, "当前输入内容，性别：" + gender + " 登录名:" + loginName, Toast.LENGTH_LONG).show();

        gridPhoto = (GridView) findViewById(R.id.gridPhoto);

        data = new ArrayList<IconBean>();
        data.add(new IconBean(R.drawable.icon_1_128, "星爸爸"));
        data.add(new IconBean(R.drawable.icon_2_128, "金拱门"));
        data.add(new IconBean(R.drawable.icon_3_128, "机器人"));
        data.add(new IconBean(R.drawable.icon_4_128, "小企鹅"));
        data.add(new IconBean(R.drawable.icon_5_128, "凯瑞肯"));
        data.add(new IconBean(R.drawable.icon_6_128, "小肥皂"));
        data.add(new IconBean(R.drawable.icon_7_128, "流浪者"));
        adapter = new GenericAdapter<IconBean>(data, R.layout.item_list) {
            @Override
            public void bindView(ViewHolder holder, IconBean obj) {
                holder.setImageResource(R.id.iconImg, obj.getImgId());
                holder.setText(R.id.iconText, obj.getIconText());
            }
        };
        gridPhoto.setAdapter(adapter);
        gridPhoto.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent it = getIntent();
                Bundle bd = new Bundle();
                bd.putInt("selectedId",data.get(position).getImgId());
                bd.putString("selectedText",data.get(position).getIconText());
                it.putExtras(bd);
                setResult(101,it);
                finish();
            }
        });
    }
    @Override
    protected void onDestroy(){
        super.onDestroy();
        ActivityCollector.getInstance().removeActivity(this);
    }
}

MainActivity.java

package org.mk.android.demo;

import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Toast;

import java.util.LinkedList;

public class MainActivity extends AppCompatActivity {

    private Button buttonRegister;
    private RadioGroup genderRG;
    private EditText edTextLoginName;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ActivityCollector.getInstance().addActivity(this);
        buttonRegister = (Button) findViewById(R.id.buttonRegister);
        genderRG = (RadioGroup) findViewById(R.id.rgGroup);
        edTextLoginName = (EditText) findViewById(R.id.edTextLoginName);
        buttonRegister.setOnClickListener(new OnClickListener());
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();
        ActivityCollector.getInstance().exit();
    }

    //下面这段是配合着老式的startActivityForResult(homeIt,101);的写法，当我们用了registerForActivityResult
    //下面这种onActivityResult就不需要写了。
    //@Override
    //protected void onActivityResult(int requestCode, int resultCode,
    //        Intent data) {
    //    super.onActivityResult(requestCode, resultCode, data);
    //    if (requestCode == 101 && resultCode == 101) {
    //        Bundle bd = data.getExtras();
    //        int imgid = bd.getInt("selectedId");
    //        String selectedContent = bd.getString("selectedText");
    //        ImageView img = (ImageView) findViewById(R.id.selectedImg);
    //        img.setImageResource(imgid);
    //        Toast.makeText(MainActivity.this, "你刚才选择的是：" + selectedContent,
    //        Toast.LENGTH_LONG).show();
    //    }
    //}

    private ActivityResultLauncher launcher = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
        if (result.getResultCode() == 101) {
            Bundle bd = result.getData().getExtras();
            int imgid = bd.getInt("selectedId");
            String selectedContent = bd.getString("selectedText");
            ImageView img = (ImageView) findViewById(R.id.selectedImg);
            img.setImageResource(imgid);
            Toast.makeText(MainActivity.this, "你刚才选择的是：" + selectedContent, Toast.LENGTH_LONG).show();
        }
    });


    private class OnClickListener implements View.OnClickListener {
        private int gender = -1;
        private String loginName = "";

        @Override
        public void onClick(View v) {
            for (int i = 0; i < genderRG.getChildCount(); i++) {
                RadioButton rb = (RadioButton) genderRG.getChildAt(i);
                if (rb.isChecked()) {
                    switch (i) {
                        case 0:
                            gender = 0;
                            break;
                        case 1:
                            gender = 1;
                            break;
                    }
                    break;
                }
            }
            loginName = edTextLoginName.getText().toString();
            //Toast.makeText(MainActivity.this, "当前输入内容，性别：" + gender + "
            // 登录名: " + loginName, Toast.LENGTH_SHORT).show();
            Log.i("app", "当前输入内容，性别：" + gender + " 登录名:" + loginName);
            transferToHomePage(loginName, gender);
        }

        private void transferToHomePage(String loginName, int gender) {
            Intent homeIt = new Intent(MainActivity.this, HomePageActivity.class);
            Bundle bd = new Bundle();
            bd.putString("loginName", loginName);
            bd.putInt("gender", gender);
            homeIt.putExtras(bd);
            //startActivity(homeIt);
            //startActivityForResult(homeIt,101);
            // 这种写法已经废弃用新的registerForActivityResult会非常优雅且不用去覆盖onActivityResult
            launcher.launch(homeIt);
        }
    }
}

传递值到子activity-HomePageActivity里使用putExtras自然没得话说。关键在于我们运行sub activity的launcher.launch(homeIt);方法。这个方法通过一个registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result ->来判断当子activity返回即调用了finish()生命周期后，可以得到子activity在finish()语句前setResult(101,it);中的内容即实现了子activity中的值回传上一层activity了。

自己请动一下手试试看吧。

附、工程结构