高级组件Application，实现全局变量共享和其他组件间通信

除开常见的四大组件，还有一个不常用的组件Application。每个应用程序都有一个Application组件，如未显式定义，系统会创建一个默认的Application。我们可以通过Application实例来实现全局变量共享和组件通信。

下面是一个例子，定义了1个自定义Application组件，1个MainActivity，2个用于演示通信的Fragment。

1.      MyApplication

sExtraData 保存组件通信的数据

sKeyRepo保存所有key值，以便演示时可以取出所有保存的值

package com.jl.test.applicationtransfertest;

import android.app.Application;
import android.util.Log;
import java.util.ArrayList;
import java.util.HashMap;


public class MyApplication extends Application {

    private final static String TAG = "MyApplicaton";

    private static MyApplication sApplication = null;
    private static HashMap
   
   
    
     sExtraData = new HashMap
    
    
     
     ();
    private static ArrayList
     
     
      
       sKeyRePo = new ArrayList
      
      
       
       ();

    public static MyApplication getApplication() {
        return sApplication;
    }

    public static ArrayList
       
       
         getAllKeys(){ return sKeyRePo; } // 组件间传递用方法 public static void putExtraData(String key,Object data){ sExtraData.put(key,data); sKeyRePo.add(key); } public static Object getExtraData(String key){ Object obj = null; if(sExtraData.containsKey(key)){ obj = sExtraData.get(key); // 为防止OOM数据使用完后应移除，这里为了演示不移除 // sExtraData.remove(key); } return obj; } @Override public void onCreate() { super.onCreate(); sApplication = this; Log.i(TAG,"application is initing."); } } 
       
      
      
     
     
    
    
   
   

在android:name属性中声明自定义的Application组件，以便系统识别

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.jl.test.applicationtransfertest" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme"
        android:name=".MyApplication">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

1.      MainActivity

根据不同的按钮显示不同的Fragment，使用Fragment可以使应用界面更加灵活，适应性更强。

package com.jl.test.applicationtransfertest;

import android.app.Activity;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;


public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        View.OnClickListener mListener = new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction ft = getFragmentManager().beginTransaction();
                switch (v.getId()){
                    case R.id.button1:
                        ft.replace(R.id.container,FragmentContent1.newInstance());
                        ft.commit();
                        break;
                    case R.id.button2:
                        ft.replace(R.id.container,FragmentContent2.newInstance());
                        ft.commit();
                        break;
                    default:
                        break;
                }
            }
        };

        Button button2Frag1 = (Button) findViewById(R.id.button1);
        Button button2Frag2 = (Button) findViewById(R.id.button2);
        button2Frag1.setOnClickListener(mListener);
        button2Frag2.setOnClickListener(mListener);

    }

}

<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:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_fragment_one"
        android:id="@+id/button1"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/button_fragment_two"
        android:id="@+id/button2"
        android:layout_alignParentTop="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"/>

    <FrameLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_below="@+id/button1"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:id="@+id/container">
    </FrameLayout>
</RelativeLayout>

3.      FragmentContent1和FragmentContent2

两个Fragment布局完全一样，代码基本一致。一个EditText接受用户输入，停止输入1.5秒后将值保存进Hashmap里，一个TextView显示数据

package com.jl.test.applicationtransfertest;


import android.app.Fragment;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.TextView;

public class FragmentContent1 extends Fragment {

    private EditText mInputText1=null;
    private TextView mOutputText1=null;

    private final static String TAG = "fragmentContent1";
    private int mContentId = 0;

    private String mPreviousContent = "";
    private String mCurrentContent = "";

    private final static int DELAY_TO_COMMIT = 1500;
    private Runnable mCommitRunnable = new Runnable() {
        @Override
        public void run() {
            mPreviousContent = mCurrentContent;
            MyApplication.putExtraData(TAG + " " + (mContentId++), mCurrentContent);
        }
    };

    public static FragmentContent1 newInstance(){
        FragmentContent1 f = new FragmentContent1();
        return f;
    }

    private void delayToCommit(){
        mInputText1.removeCallbacks(mCommitRunnable);

        if(mCurrentContent.length()>0&&!mPreviousContent.equals(mCurrentContent)){
            mInputText1.postDelayed(mCommitRunnable,DELAY_TO_COMMIT);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_content1,container,false);

            mInputText1 = (EditText) v.findViewById(R.id.editText1);
            mOutputText1 = (TextView) v.findViewById(R.id.textView1);
            mInputText1.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                int length = mInputText1.getText().toString().length();
                if(length>0){
                    mCurrentContent = mInputText1.getText().toString();
                    delayToCommit();
                }

            }
        });

        mOutputText1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                StringBuilder mBuilder = new StringBuilder();
                for (String tempKey:MyApplication.getAllKeys()) {
                    mBuilder.append(tempKey).append(":").append(MyApplication.getExtraData(tempKey)).append("\n");
                }
                mOutputText1.setText(mBuilder);
            }
        });

        return v;

    }
}

<LinearLayout 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:orientation="vertical"
    tools:context="com.jl.test.applicationtransfertest.FragmentContent1">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:id="@+id/editText1"
        android:hint="@string/hint_text"
        android:layout_gravity="start|top"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/textView1"
        />

</LinearLayout>