Android 计时器的实现

效果图如下：

布局文件如下：

<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">    <TextView        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:id="@+id/textView"        android:padding="20dp"        android:text="00:00.0"        android:textSize="36sp" />    <LinearLayout        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:orientation="horizontal"        android:layout_below="@+id/textView"        android:id="@+id/linearLayout">        <Button            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:id="@+id/start"            android:text="@string/start_button"            android:layout_weight="1"            />        <Button            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:id="@+id/stop"            android:text="@string/stop_button"            android:layout_weight="1"            />        </LinearLayout></RelativeLayout>

代码如下：

/* * Copyright (c) 2015. 版权归5hand所有 */package com.example.dell.myapplication;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.support.v7.app.ActionBarActivity;import android.view.KeyEvent;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends ActionBarActivity {    private long time;    private TextView textView;    private Handler handler = new Handler() {        @Override        public void  handleMessage(Message msg) {            String str = String.format("%1$tM:%1$tS.%1$1tL", System.currentTimeMillis() - time);            textView.setText(str.substring(0, 7));            handler.sendEmptyMessageDelayed(0, 100);        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        time = System.currentTimeMillis();        textView = (TextView) findViewById(R.id.textView);        Button startButton = (Button) findViewById(R.id.start);        startButton.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                handler.sendEmptyMessage(0);            }        });        Button stopButton = (Button) findViewById(R.id.stop);        stopButton.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                if (handler.hasMessages(0)) {                    handler.removeMessages(0);                }            }        });    }    @Override    public boolean onKeyDown(int keyCode, KeyEvent event) {        switch (keyCode) {            case KeyEvent.KEYCODE_BACK:                Toast.makeText(MainActivity.this, "再按一次退出程序", Toast.LENGTH_SHORT).show();                return true;            default:                return super.onKeyDown(keyCode, event);        }    }}

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