android小技巧:在activity中實現與綁定的fragment的回調

看到標題你可能會想是一個多麼高大上的技巧呢?其實很一般就是自定義回調函數.

首先我們知道activity之間的數據傳遞有幾種方式:

一是startActivityForResut()啟動一個activity,當棧頂activity 調用onActivityResult()並且 finish 掉時將會傳遞消息給啟動該activity的父activity.

二是在使用Fragment時,通過setTargetFragment()和onActivityResult()方法實現兩個fragment之間的數據傳遞.

上述兩種方式對於操作傳遞復雜數據時會很有幫助,但是對於簡單數據或者僅僅是喚醒某步操作,並且不一定在子activity或fragment(這裡到子代表由父activity啟動的下一個activity或fragment)finish掉時就進行操作很有幫助.<喎?/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+PGJyPgo8L3A+CjxwPrrDwcsssNe7sMHLxMfDtLbgsrvP4LjJtcQs1PjLr771x7DQtMG90NC0+sLrzPnJz8jDtPO80rjQytzSu8/COjwvcD4KPHA+ztLV4sDvytfPyLS0vajBy9K7uPaz6c/zwOC8zLPQ19RWNMCp1bm/4rXERnJhZ21lbnRBY3Rpdml0ecC0udzA7cO/uPZGcmFnbWVudLXEtLS9qDwvcD4KPHA+PHByZSBjbGFzcz0="brush:java;">package com.example.icedcap.fragmentcallbackdemo; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentActivity; import android.support.v4.app.FragmentManager; /** * Created by icedcap on 14-11-18. */ public abstract class SingleFragment extends FragmentActivity { public abstract Fragment createFragment(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_my); FragmentManager fm = getSupportFragmentManager(); Fragment mFragment = fm.findFragmentById(R.id.container); if (mFragment == null){ mFragment = createFragment(); fm.beginTransaction().add(R.id.container, mFragment).commit(); } } }
這樣我在主activity中只需繼承該抽象類並且實現createFragment方法就能輕松創建一個Fragment並且將其添加到R.id.container容器上了.

    @Override
    public Fragment createFragment() {
        return new IndexFragment();
    }

對於Fragment很簡單我只加了一個TextView和一個Button控件,當點擊Button時,喚醒回調函數,使activity的回調函數進行工作.

package com.example.icedcap.fragmentcallbackdemo;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

/**
 * Created by icedcap on 14-11-18.
 */
public class IndexFragment extends Fragment {
    private IndexListener mListener;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_index, container, false);
        Button button = (Button) v.findViewById(R.id.index_button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mListener.onIndexListener("Call Back to My Implementer");
            }
        });
        return v;
    }

    public interface IndexListener{
        public void onIndexListener(String str);
    }

    //初始化mListener
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        try {
            mListener = (IndexListener) activity;
        }catch (ClassCastException e){
            throw new ClassCastException(activity.toString() + " must implement IndexListener");
        }
    }
}

在主activity完成回調函數的任務

package com.example.icedcap.fragmentcallbackdemo;

import android.support.v4.app.Fragment;
import android.util.Log;

public class MyActivity extends SingleFragment implements IndexFragment.IndexListener{
    private static final String TAG = "MyActivity";

    @Override
    public Fragment createFragment() {
        return new IndexFragment();
    }

    @Override
    public void onIndexListener(String str) {
        Log.d(TAG, "From the Fragment message: " + str);
    }
}

當點擊Fragment中的Button時,Logcat會打印這樣一句話:

From the Fragment message: Call Back to My Implementer

好了,代碼結束!

這個例子看上去貌似沒啥意義,但是對於一些應用場合還是很重要的,例如,在文件管理器中搜索功能,當鍵入一些字符串時,就會立即返回結果用戶不必輸入整個要查詢的文件名稱就能檢索出結果來,正是利用EditText的addTextChangeListener事件並手動添加了後台檢索方法的類來監聽afterTextchange函數裡所獲取到底殘缺字符串.

好了,弄明白監聽對象和喚醒監聽對象的兩個類後使很容易寫出簡介易懂的代碼的.