Android Activity之启动其他Activity并返回结果

在Android的Activity传递中，有时候因项目需要，不仅需要从当前Activity切换到另一个Activity，还需要从另一个Activity获取返回的数据，供当前Activity使用。

本例包含两个Activity，第一个Activity只有一个Button和TextView，Button用于切换到另一个Activity选择城市，TextView用于显示结果；另一个Activity使用的是ExpandableListActivity（可展开列表），用于显示供选择的城市。

1.MainActivity：

package com.example.activityforresult;import android.content.Intent;import android.support.annotation.Nullable;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;public class MainActivity extends AppCompatActivity {    public Button select;    public TextView show;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        select = findViewById(R.id.select);        show = findViewById(R.id.show);        //绑定监听器        select.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                //创建需要对应于目标Activity的Intent                Intent intent = new Intent(MainActivity.this , SelectCityActivity.class);                //启动指定Activity并等待返回结果，其中0是请求码，用于标识该请求                startActivityForResult(intent , 0);            }        });    }    @Override    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent intent) {        //当requestCode、resultCode同为0时，处理待定的结果        if (requestCode == 0 && resultCode == 0){            //取出Intent中的Extras数据            Bundle data = intent.getExtras();            //取出Bundle中的数据            String resultCity = data.getString("city");            //将获得的数据显示到文本框中            show.setText(resultCity);        }    }}

2.SelectCityActivity：

package com.example.activityforresult;import android.app.ExpandableListActivity;import android.content.Intent;import android.os.Bundle;import android.os.PersistableBundle;import android.view.Gravity;import android.view.View;import android.view.ViewGroup;import android.widget.AbsListView;import android.widget.BaseExpandableListAdapter;import android.widget.ExpandableListAdapter;import android.widget.ExpandableListView;import android.widget.ImageView;import android.widget.LinearLayout;import android.widget.TextView;public class SelectCityActivity extends ExpandableListActivity {    //定义省份数组    private String[] provinces = new String[]{            "广东" , "广西" , "湖南"    };    //定义城市数组    private String[][] cities = new String[][]{            {"广州" , "深圳" , "珠海" , "中山"} ,            {"桂林" , "柳州" , "南宁" , "北海"} ,            {"长沙" , "岳阳" , "衡阳" , "株洲"}    };    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        ExpandableListAdapter adapter = new BaseExpandableListAdapter() {            private TextView getTextView(){                AbsListView.LayoutParams lp = new AbsListView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT , 64);                TextView textView = new TextView(SelectCityActivity.this);                textView.setLayoutParams(lp);                textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);                textView.setPadding(36 , 0, 0 , 0);                textView.setTextSize(20);                return textView;            }            //获取指定组位置、指定子列表项处的子列表数据            @Override            public int getGroupCount() {                return provinces.length;            }            @Override            public int getChildrenCount(int groupPosition) {                return cities[groupPosition].length;            }            @Override            public Object getGroup(int groupPosition) {                return provinces[groupPosition];            }            @Override            public Object getChild(int groupPosition, int childPosition) {                return cities[groupPosition][childPosition];            }            @Override            public long getGroupId(int groupPosition) {                return groupPosition;            }            @Override            public long getChildId(int groupPosition, int childPosition) {                return childPosition;            }            @Override            public boolean hasStableIds() {                return true;            }            //该方法决定每个组选项的外观            @Override            public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {                LinearLayout ll = new LinearLayout(SelectCityActivity.this);                ll.setOrientation(LinearLayout.HORIZONTAL);                ImageView logo = new ImageView(SelectCityActivity.this);                ll.addView(logo);                TextView textView = getTextView();                textView.setText(getGroup(groupPosition).toString());                ll.addView(textView);                return ll;            }            //该方法决定每个子选项的外观            @Override            public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {                TextView textView = getTextView();                textView.setText(getChild(groupPosition , childPosition).toString());                return textView;            }            @Override            public boolean isChildSelectable(int groupPosition, int childPosition) {                return true;            }        };        setListAdapter(adapter);        getExpandableListView().setOnChildClickListener(new ExpandableListView.OnChildClickListener() {            @Override            public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {                //获取启动该Activity之前的Activity对应的Intent                Intent intent = getIntent();                intent.putExtra("city" , cities[groupPosition][childPosition]);                //设置结果码，并设置结束之后退回的Activity                SelectCityActivity.this.setResult(0 , intent);                SelectCityActivity.this.finish();                return false;            }        });    }}

3.MainActivity的XML布局文件 activity_main.xml（SelectCityActivity无XML，布局用java代码实现）：

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

4.前面由于有两个Activity：MainActivity和SelectCityActivity，其中MainActivity在创建时会自动声明，SelectCityActivity需要在AndroidManifest.xml中自己声明，不然程序会报错：

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