Android四大组件之——Activity的开启：StartActivity()和StartActivityForResult()（图文详解）

     

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      [Android四大组件学习系列Activity篇]

       1.Android四大组件之——Activity(一)定义、状态和后退栈(图文详解)

       2.Android四大组件之——Activity的生命周期（图文详解)

       3.Android四大组件之——Activity的开启StartActivity()和StartActivityForResult()（图文详解）

      前两次学习了Activity的基本概念和生命周期，今天学习一下Activity的跳转和值传递。

      废话不多说，开始学习！

• Activity的开启

       开启一个新的Activity有两种方法:

                          startActivity(Intent)和startActivityForResult(Intent,int)。

      startActivity(Intent):

                        用于开启一个新的Activity，新Activity压入栈顶。参数Intent用于描述新Activity。

      startActivityForResult(Intent,int):

                        用于开启新Activity，新Activity退出后，返回结果给旧Activity。 

     startActivity好理解，startActivityForResult()就麻烦一点，下面这张图方便我们的理解:

     

          说明一下:

               requestCode,请求码,自己随意设置，但必须是非负数。只有是非负数时，Activity退出时，这个码会返回到onActivityResult()。

               resultCode，结果码，用于标识返回数据来自于哪个新Activity,它的值一般是

               RESULT_CANCELED, RESULT_OK， RESULT_FIRST_USER。

          写了一个关于开启Activity的Demo：

          共三个Activity：MainActivity用户填写用户姓名电话城市、CityActivity用于用户选择城市,ShowActivity用于展示用户信息。

          MainActivity:

package com.johntsai.startactivity;

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract.CommonDataKinds.Phone;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity implements OnClickListener {
   
    private Button button_city,button_phone,button_save;
    private EditText editText_city,editText_name,editText_phone;
    private static final int SELECT_CITY_REQUEST =2;
    private static final int SELECT_PHONE_REQUEST =3;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
       button_city = (Button)findViewById(R.id.button_city);
       button_phone = (Button)findViewById(R.id.button_phone);
       button_save = (Button)findViewById(R.id.button_save);
       editText_city = (EditText)findViewById(R.id.editText_city);
       editText_name = (EditText)findViewById(R.id.editText_name);
       editText_phone = (EditText)findViewById(R.id.editText_Phone);
       
       button_city.setOnClickListener(this);
       button_phone.setOnClickListener(this);
       button_save.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
         switch (v.getId()) {
        case R.id.button_city:
            Intent i = new Intent ();
            i.setClass(MainActivity.this, CityActivity.class);
            startActivityForResult(i, SELECT_CITY_REQUEST);
            break;
        case R.id.button_phone:
             Intent pickContactIntent = new Intent(Intent.ACTION_PICK, Uri.parse("content://contacts"));
             pickContactIntent.setType(Phone.CONTENT_TYPE);
             startActivityForResult(pickContactIntent, SELECT_PHONE_REQUEST);
            break;
        case R.id.button_save:
            String name=editText_name.getText().toString();
            String city = editText_city.getText().toString();
            String phone = editText_phone.getText().toString();
            Intent saveIntent = new Intent(MainActivity.this,ShowActivity.class);
            saveIntent.putExtra("content", "NAME: "+name+"
CITY:   "+city+"
PHONE"+phone);
            startActivity(saveIntent);
            break;
        default:
            break;
        }        
    }
    
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if(SELECT_CITY_REQUEST == requestCode){
            if(resultCode ==RESULT_OK){
                String city = data.getStringExtra("city");
                editText_city.setText(city);
            }
        }
        if(SELECT_PHONE_REQUEST == requestCode){
            if(resultCode == RESULT_OK){
                 Uri contactData = data.getData();
                 String [] projection ={Phone.NUMBER};
                 Cursor c = getContentResolver()
                         .query(contactData, projection, null, null, null);
                 c.moveToFirst();
                 int column =c.getColumnIndex(Phone.NUMBER);
                 String num = c.getString(column);  
                 editText_phone.setText(num);
            }
        }
        super.onActivityResult(requestCode, resultCode, data);
    }
}

package com.johntsai.startactivity;


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
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.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

public class CityActivity extends Activity {
    
     private     ExpandableListView eListView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
      
         super.onCreate(savedInstanceState);
         setContentView(R.layout.layout_city);
         initEListView();
    }
     
     //初始化
     private void initEListView(){
            ExpandableListAdapter adapter = new BaseExpandableListAdapter() {
                
       
                private String [] countries = new String[]{
                        "China","USA","UK"
                };
                
                private String [][] cities = new String[][]{
                        {"BeiJing","ShangHai","HongKong","TaiBei"},
                        {"Washington","New York","Los Angles","San Fransico"},
                        {"London","Manchester","Birmingham","Liverpool"}
                };
                private TextView getTextView(){
                    AbsListView.LayoutParams lp = new AbsListView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
                            ViewGroup.LayoutParams.WRAP_CONTENT);
                    TextView textView = new TextView(CityActivity.this);
                    textView.setLayoutParams(lp);
                    textView.setGravity(Gravity.CENTER_HORIZONTAL);
                    textView.setPadding(0, 0, 0, 0);
                    textView.setTextSize(20);
                    return textView;
                    
                }
                @Override
                public boolean isChildSelectable(int groupPosition, int childPosition) {
                    Toast.makeText(CityActivity.this, "you have clicked Group:"+groupPosition+"Child:"+childPosition+"
"+countries[groupPosition]+"  "+cities[groupPosition][childPosition], 
                            Toast.LENGTH_SHORT).show();
                    Intent i = new Intent();
                    i.putExtra("city", cities[groupPosition][childPosition]);
                    setResult(RESULT_OK, i);
                    finish();
                    return true;
                } 
                
                @Override
                public boolean hasStableIds() {
                    return true;
                }
                
                @Override
                public View getGroupView(int groupPosition, boolean isExpanded,
                        View convertView, ViewGroup parent) {
                    LinearLayout linearLayout = new LinearLayout(CityActivity.this);
                    linearLayout.setOrientation(0);
                    
                    TextView textView = getTextView();
                    textView.setText(getGroup(groupPosition).toString());
                    linearLayout.addView(textView);
                    return linearLayout;
                }
                @Override
                public long getGroupId(int groupPosition) {
                    return groupPosition;
                }
                
                @Override
                public int getGroupCount() {
                    return countries.length;
                }
                
                @Override
                public Object getGroup(int groupPosition) {
                    return countries[groupPosition];
                }
                
                @Override
                public int getChildrenCount(int groupPosition) {
                    return cities[groupPosition].length;
                }
                
                @Override
                public View getChildView(int groupPosition, int childPosition,
                        boolean isLastChild, View convertView, ViewGroup parent) {
                     TextView textView = getTextView();
                     textView.setText(getChild(groupPosition, childPosition).toString());
                     textView.setGravity(Gravity.CENTER_HORIZONTAL);
                     return textView;
                }
                
                @Override
                public long getChildId(int groupPosition, int childPosition) {
                      return childPosition;
                }
                
                @Override
                public Object getChild(int groupPosition, int childPosition) {
                    return cities[groupPosition][childPosition];
                }
            };
             eListView = (ExpandableListView)findViewById(R.id.expandableListView);
             eListView.setAdapter(adapter);
     }
}

package com.johntsai.startactivity;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TextView;

public class ShowActivity extends Activity {
    private TextView showTextView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.layout_show);
         showTextView = (TextView)findViewById(R.id.textView_show);
         
         Intent i =getIntent();
         String content = i.getStringExtra("content");
         showTextView.setText(content);
    }
}

Demo运行效果图

                      

                        

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