Android 判断actvitiy是否在前台 activity check

遇到这样的需求是：点击进入一个listview，每个item需要一个checkbox来进行勾选，当退出该activity之后，再次进入该activity之后，需要看到上次退出时候的checkbox的状态，得益于这位前辈的博文已经讲得很好了：listview checkbox 保留状态  可以参考一下，他是默认是不选中，而我的需求第一次进入是全部选中：

主要控制代码如下：SelectInstrumentActivity.java：

package client.verbank.mtp.allone.frame.systemsettings.nextpage;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import jedi.verbank.CSTS3.comm.struct.Instrument;
import jedi.verbank.client.station.api.doc.APIDoc;
import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import client.verbank.mtp.allone.R;
import client.verbank.mtp.allone.frame.systemsettings.nextpage.SelectInstrumentActivityAdapter.ViewHolder;
import client.verbank.mtp.allone.util.SharepreferencesUtilSystemSettings;

public class SelectInstrumentActivity extends Activity {

	List<Map<String, Object>> listems;
	Map<Integer, Boolean> ifchose = new HashMap<Integer, Boolean>();

	private ListView lv;
	private SelectInstrumentActivityAdapter mAdapter;
	private ArrayList<String> list;
	private Button bt_selectall;
	private Button bt_cancel;
	private Button bt_deselectall;

	private Button newsback;
	private int checkNum; // 记录选中的条目数量
	private TextView tv_show;// 用于显示选中的条目数量

	private Boolean flag = false;
	private int id;// 消息编号，用来存储故障标号，从上一个界面传来
	private String defaul = "";// 默认的全部不勾选
	private String selectall = "";// 全部勾选

	/** Called when the activity is first created. */

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_systemsettings_selectinstrument);
		// Intent i = getIntent();
		// Bundle b = i.getBundleExtra("ID");
		// id = b.getInt("id");

		/* 实例化各个控件 */
		lv = (ListView) findViewById(R.id.systeminstrumentlistview);
		bt_selectall = (Button) findViewById(R.id.bt_selectall);
		bt_cancel = (Button) findViewById(R.id.bt_cancleselectall);
		bt_deselectall = (Button) findViewById(R.id.bt_deselectall);
		tv_show = (TextView) findViewById(R.id.tv);
		newsback = (Button) findViewById(R.id.newsback);
		list = new ArrayList<String>();

		// 为Adapter准备数据
		initDate();
		<span style="font-size:18px;color:#ff0000;"><strong>if (!flag) {   //flag标志是为了识别是否为第一次进入全部勾选，当第二次进入默认不勾选，让用户勾选
			// 初始化勾选框信息，默认都是以未勾选为单位
			for (int n = 0; n < list.size(); n++) {
				defaul = defaul + "1";

			}
			flag = true;
		} else {
			// 初始化勾选框信息，默认都是以未勾选为单位
			for (int n = 0; n < list.size(); n++) {
				defaul = defaul + "0";
				selectall = selectall + "1";
			}
		}</strong></span>

		// 实例化自定义的MyAdapter
		mAdapter = new SelectInstrumentActivityAdapter(list, this);
		// 绑定Adapter
		lv.setAdapter(mAdapter);
		getCheck();// 获取信息，也可说是初始化信息

		newsback.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {

				String str = "";// 确定后直接将信息写入preference保存以备下一次读取使用

				for (int i = 0; i < list.size(); i++) {
					if (SelectInstrumentActivityAdapter.getIsSelected().get(i)) {
						str = str + '1';
					} else {
						str = str + '0';
					}
				}

				saveCheck(String.valueOf(id), str);// 将数据已字符串形式保存起来，下次读取再用

				String inarray = SharepreferencesUtilSystemSettings.getValue(
						getApplicationContext(), "instrument", "AUD/CHF");

				String[] as = inarray.split(",");
				StringBuilder str2 = new StringBuilder("");
				for (int i = 0; i < as.length; i++) {
					str2.append(as[i]);
				}

				finish();

			}
		});

		// 全选按钮的回调接口
		bt_selectall.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// 遍历list的长度，将MyAdapter中的map值全部设为true
				for (int i = 0; i < list.size(); i++) {
					SelectInstrumentActivityAdapter.getIsSelected()
							.put(i, true);
				}
				// 数量设为list的长度
				checkNum = list.size();

				StringBuilder strall = new StringBuilder("");
				for (String selstr : list) {
					strall.append(selstr).append(",");
				}

				SharepreferencesUtilSystemSettings.putValue(
						getApplicationContext(), "instrument",
						strall.toString());
				tv_show.setText("已选中" + checkNum + "项");

				// 刷新listview和TextView的显示
				dataChanged();
			}
		});

		// 反选按钮的回调接口
		bt_cancel.setOnClickListener(new OnClickListener() {
			StringBuilder strfan = new StringBuilder("");

			@Override
			public void onClick(View v) {
				strfan.delete(0, strfan.capacity());
				// 遍历list的长度，将已选的设为未选，未选的设为已选
				for (int i = 0; i < list.size(); i++) {
					if (SelectInstrumentActivityAdapter.getIsSelected().get(i)) {
						SelectInstrumentActivityAdapter.getIsSelected().put(i,
								false);
						checkNum--;
					} else {
						SelectInstrumentActivityAdapter.getIsSelected().put(i,
								true);

						strfan.append(list.get(i)).append(",");

						SharepreferencesUtilSystemSettings.putValue(
								getApplicationContext(), "instrument",
								strfan.toString());

						checkNum++;
					}
				}

				// 刷新listview和TextView的显示
				dataChanged();
			}
		});

		// 取消按钮的回调接口
		bt_deselectall.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// 遍历list的长度，将已选的按钮设为未选
				for (int i = 0; i < list.size(); i++) {
					if (SelectInstrumentActivityAdapter.getIsSelected().get(i)) {
						SelectInstrumentActivityAdapter.getIsSelected().put(i,
								false);
						checkNum--;// 数量减1
					}
				}
				SharepreferencesUtilSystemSettings.putValue(
						getApplicationContext(), "instrument", "");

				// 刷新listview和TextView的显示
				dataChanged();
			}
		});

		final StringBuilder str = new StringBuilder("");
		// 绑定listView的监听器
		lv.setOnItemClickListener(new OnItemClickListener() {
			@Override
			public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
					long arg3) {
				// 取得ViewHolder对象，这样就省去了通过层层的findViewById去实例化我们需要的cb实例的步骤
				ViewHolder holder = (ViewHolder) arg1.getTag();
				// 改变CheckBox的状态
				holder.cb.toggle();
				// 将CheckBox的选中状况记录下来
				SelectInstrumentActivityAdapter.getIsSelected().put(arg2,
						holder.cb.isChecked());

				// 调整选定条目
				if (holder.cb.isChecked() == true) {
					str.delete(0, str.capacity());
					checkNum++;
				} else {
					str.delete(0, str.capacity());
					checkNum--;

				}
				for (int i = 0; i < list.size(); i++) {
					if (SelectInstrumentActivityAdapter.getIsSelected().get(i)) {

						str.append(list.get(i)).append(",");

					}
				}
				SharepreferencesUtilSystemSettings.putValue(
						getApplicationContext(), "instrument", str.toString());

				tv_show.setText("已选中" + checkNum + "项");
			}
		});
	}

	// 初始化数据
	private void initDate() {
		// 去掉相同的商品
		List<Instrument> instList = APIDoc.getSystemDocCaptain()
				.getInstrumentList();
		for (Instrument instrument : instList) {

			list.add(instrument.getInstrument());

		}
	}

<span style="font-size:18px;color:#ff0000;"><strong>	// 得到保存在这个activity中的数据
	public void getCheck() {

		SharedPreferences mPerferences = PreferenceManager
				.getDefaultSharedPreferences(this);// 获取默认的preference

		// 获取activity私有的preference
		SharedPreferences m_private = this.getPreferences(MODE_PRIVATE);
		String counter = mPerferences.getString(String.valueOf(id), defaul);// 如果没有获取到的话默认是0

		for (int i = 0; i < list.size(); i++) {
			if (counter.charAt(i) == '1') {
				SelectInstrumentActivityAdapter.getIsSelected().put(i, true);
			}
		}

	}

	// 保存需要保存的数据
	public void saveCheck(String ID, String data) {
		// 保存shuju
		SharedPreferences mPerferences = PreferenceManager
				.getDefaultSharedPreferences(this);
		SharedPreferences m_private = this.getPreferences(MODE_PRIVATE);
		SharedPreferences.Editor mEditor = mPerferences.edit();

		mEditor.putString(ID, data);
		mEditor.commit();
	}</strong></span>

	// 刷新listview和TextView的显示
	private void dataChanged() {
		// 通知listView刷新
		mAdapter.notifyDataSetChanged();
		// TextView显示最新的选中数目
		tv_show.setText("已选中" + checkNum + "项");
	};
}

适配器类：SelectInstrumentActivityAdapter.java

package client.verbank.mtp.allone.frame.systemsettings.nextpage;

import java.util.ArrayList;
import java.util.HashMap;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.TextView;
import client.verbank.mtp.allone.R;

public class SelectInstrumentActivityAdapter extends BaseAdapter {
	// 填充数据的list
	private ArrayList<String> list;
	// 用来控制CheckBox的选中状况
	private static HashMap<Integer, Boolean> isSelected;
	// 上下文
	private Context context;
	// 用来导入布局
	private LayoutInflater inflater = null;

	// 构造器
	public SelectInstrumentActivityAdapter(ArrayList<String> list,
			Context context) {
		this.context = context;
		this.list = list;
		inflater = LayoutInflater.from(context);
		isSelected = new HashMap<Integer, Boolean>();
		// 初始化数据
		initDate();
	}

	// 初始化isSelected的数据
	private void initDate() {
		for (int i = 0; i < list.size(); i++) {
			getIsSelected().put(i, false);
		}
	}

	@Override
	public int getCount() {
		return list.size();
	}

	@Override
	public Object getItem(int position) {
		return list.get(position);
	}

	@Override
	public long getItemId(int position) {
		return position;
	}

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		ViewHolder holder = null;
		if (convertView == null) {
			// 获得ViewHolder对象
			holder = new ViewHolder();
			// 导入布局并赋值给convertview
			convertView = inflater.inflate(
					R.layout.activity_systeminstrument_item, null);
			holder.tv = (TextView) convertView.findViewById(R.id.item_tv);
			holder.cb = (CheckBox) convertView.findViewById(R.id.item_cb);
			// 为view设置标签
			convertView.setTag(holder);
		} else {
			// 取出holder
			holder = (ViewHolder) convertView.getTag();
		}
		// 设置list中TextView的显示
		holder.tv.setText(list.get(position));
		// 根据isSelected来设置checkbox的选中状况
		holder.cb.setChecked(getIsSelected().get(position));
		return convertView;
	}

	public static HashMap<Integer, Boolean> getIsSelected() {
		return isSelected;
	}

	public static void setIsSelected(HashMap<Integer, Boolean> isSelected) {
		SelectInstrumentActivityAdapter.isSelected = isSelected;
	}

	public static class ViewHolder {
		TextView tv;
		CheckBox cb;
	}
}

主要要实现保存checkbox的状态的方式使用sharepreferences来保存状态，当选中的时候为1，不选中的时候为0，当再次进入该activity时，使用charat方式来取出每个listview item的状态是为1还是0，接着使用：

SelectInstrumentActivityAdapter.getIsSelected().put(i, true);

来设置状态。