在工作中我们经常会遇到Activity和Fragment交互，传递数据是比较容易实现，但是要用到Activity和Fragment之间互相改变彼此的UI，网上关于这个问题的解决方法还是很少的，我也没遇到合适的解决方案，自己在前人的基础上研究后创造了一种方法。使Activity和Fragment共享一个Handler，然后发送消息通知彼此更新。别的也不多说了，例子代码如下，

这是Activity的代码：

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package com.example.fragmentandactivity;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v4.app.FragmentActivity;
import android.view.KeyEvent;
import android.widget.Toast;

public class MainActivity extends FragmentActivity {
private Handler mHandler;
private long lastPressBack;
private boolean isFirstPressBack = true;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
getSupportFragmentManager().beginTransaction()
.replace(R.id.fragment_content, new HomeFragment())
.commit();
}

public boolean onKeyDown(int keyCode, KeyEvent event) {
super.onKeyDown(keyCode, event);
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
if(HomeFragment.changeText){
Message msg = mHandler.obtainMessage();
msg.what =0;
mHandler.sendMessage(msg);
HomeFragment.changeText=false;
return false;
}
if (!isFirstPressBack) {
if (System.currentTimeMillis() - lastPressBack > 2 * 1000) {
lastPressBack = System.currentTimeMillis();
} else {
finish();
}
}
lastPressBack = System.currentTimeMillis();
Toast.makeText(this,getString(R.string.exit_app),Toast.LENGTH_SHORT).show();
isFirstPressBack = false;
return false;
}

return false;
}
public void setHandler(Handler handler) {
mHandler = handler;
}
}

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这是Fragment的代码：

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package com.example.fragmentandactivity;

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

public class HomeFragment extends Fragment{
private TextView text;
private MainActivity mActivity;
public static boolean changeText=true;
Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 0:
text.setText(ChangedFragment);
break;
}
}
};
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);

View view = inflater.inflate(R.layout.home_fragment, null);
text=(TextView)view.findViewById(R.id.text);
return view;
}
public void onAttach(Activity activity) {
super.onAttach(activity);
mActivity = (MainActivity) activity;
mActivity.setHandler(handler);
}
public void onDestroy(){
super.onDestroy();
changeText=true;
}
}