androidの常用基础应用知识总结

androidの常用基础应用知识总结

1, canvas.drawBitmap()使图片全屏显示
有时候我们这使用canvas.drawBitmap()时，需要使图片全屏显示，这个时候我们可以这样：

DisplayMetrics displaymetrics = new DisplayMetrics();
height = getResources().getDisplayMetrics().heightPixels;
width = getResources().getDisplayMetrics().widthPixels;
Rectf rectF = new RectF(0, 0, width, height ); //屏幕宽和高
canvas.drawBitmap(bitmap, null, rectF, null);

2. 返回键与Home键区别

back键默认行为是finish处于前台的Activity的即Activity的状态为Destroy状态为止，再次启动该Activity是从onCreate开始的(不会调用onSaveInstanceState方法)。Home键默认是stop前台的Activity即状态为onStop为止而不是Destroy,若再次启动它，会调用onSaveInstanceState方法，保持上次Activity的状态则是从OnRestart开始的---->onStart()--->onResume()。

3. android:paddingLeft与android:layout_marginLeft的区别

当按钮分别设置以上两个属性时，得到的效果是不一样的。

android:paddingLeft="30px" 按钮上设置的内容（例如图片）离按钮左边边界30个像素

android:layout_marginLeft="30px" 整个按钮离左边设置的内容30个像素

4 判断当前网络状态

<span style="font-size:18px;">import android.net.ConnectivityManager;
import android.net.NetworkInfo;
public boolean isNetworkConnected() {
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo ni = cm.getActiveNetworkInfo();
return ni != null && ni.isConnectedOrConnecting();
}</span>

5. 应用权限

<!-- 必须申明的权限 -->
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.RESTART_PACKAGES"/>
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
<uses-permission android:name="android.permission.GET_TASKS" />
<uses-permission android:name="android.permission.VIBRATE"/>

6.. 设置activity 一直竖屏

<activity android:name=".MainActivity" android:screenOrientation="nosensor"></activity>

7. 设置屏幕一直亮

getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

8. 设置进入界面加载过程，避免黑屏或者白屏现象

<style name="Theme.NoDisplay" parent="@android:Theme">
<item name="android:windowBackground">@null</item>
<item name="android:windowContentOverlay">@null</item>
<item name="android:windowIsTranslucent">false</item>
<item name="android:windowAnimationStyle">@null</item>
<item name="android:windowDisablePreview">true</item>
<item name="android:windowNoDisplay">false</item>
</style>

在主配置文件中，主函数中添加 android:theme="@style/Theme.NoDisplay"

9. 检查手机应用是否安装指定apk

boolean d() {
String packageName = "com.iflytek.speechcloud";
List<PackageInfo> packages = getPackageManager().getInstalledPackages(0);
for (int i = 0; i < packages.size(); i++) {
PackageInfo packageInfo = packages.get(i);
if (packageInfo.packageName.equals(packageName)) {
return true;
} else {
continue;
}
}
return false;<span style="background-color: inherit; font-family: 微软雅黑;">}</span>

10. 设置屏幕无title
import android.view.Window;
requestWindowFeature(Window.FEATURE_NO_TITLE);

11. back 键监听

public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
exitApp();
return true;
}
return super.onKeyDown(keyCode, event);
}

12 .弹出对话框选项

new AlertDialog.Builder(IndexActivity.this)
.setTitle(getString(R.string.exittitle))
.setMessage(getString(R.string.exit))
.setIcon(R.drawable.iconapp)
.setPositiveButton(getString(R.string.ok),
new DialogInterface.OnClickListener() {
public void onClick(
DialogInterface paramDialogInterface,
int paramInt) {
}
})
.setNegativeButton(getString(R.string.cancel),
new DialogInterface.OnClickListener() {
public void onClick(
DialogInterface paramDialogInterface,
int paramInt) {
finish();
}
}).show();

13.获取设备管理，设备标示名称
Build bd = new Build();
String model = bd.MODEL; //poineer sw590
String brand=bd.BRAND; //poineer

14. 如何防止暴力点击button
（可以加个计时器，1～3秒后才可以点击第二下）
private Handler mHandler =new Handler();

public void onClick(View v){

v.setEnabled(false);

mHandler.postDelay(new Runable(){

public void run(){

v.setEnabled(true);

}

}),2000);

}

15.. GirdView 添加单个item 选择上的效果

点击后，图片周围出现绿色边框效果。
属性： pictureGridView.setSelector(R.drawable.menuitemshape);
然后在 drawable文件下，添加：menuitemshape.xml 文件
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle" >
<!-- <solid android:color="#FF0000" /> -->
<stroke
android:width="2dip"
android:color="#00FF00" />
<corners android:radius="10dip" />
<padding
android:bottom="5dp"
android:left="5dp"
android:right="5dp"
android:top="7dp" />
</shape>

16.屏幕边框为椭圆形，边角为弧形，不是直角

首先在布局文件中：定义一个外布局，设置：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@color/black"
android:orientation="vertical" >
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_margin="3px"
android:background="@drawable/round_rect_shape"
android:orientation="vertical" >

然后在drawable文件下，添加round_rect_shape.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle" >
<!-- Customize round rect -->
<stroke
android:width="2dip"
android:color="#FF99CC" />
<gradient
android:angle="90"
android:endColor="#99CCFF"
android:startColor="#99CCFF" /> <!-- #474C48 -->
<corners android:radius="5dip" />
</shape>

17. 图库使用

startActivity(new Intent(
Intent.ACTION_VIEW,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI)
.putExtra("slideshow", true).addFlags(
Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP));

18.home 键使用

startActivity(new Intent(Intent.ACTION_MAIN)
.addFlags( Intent.FLAG_ACTIVITY_NEW_TASK
| Intent.FLAG_ACTIVITY_CLEAR_TOP)
.addCategory(Intent.CATEGORY_HOME));

19.拼音转换工具类

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import net.sourceforge.pinyin4j.PinyinHelper;
import net.sourceforge.pinyin4j.format.HanyuPinyinCaseType;
import net.sourceforge.pinyin4j.format.HanyuPinyinOutputFormat;
import net.sourceforge.pinyin4j.format.HanyuPinyinToneType;
import net.sourceforge.pinyin4j.format.HanyuPinyinVCharType;
import net.sourceforge.pinyin4j.format.exception.BadHanyuPinyinOutputFormatCombination;
public class PinyinUtil {
/**
* @param list
* @return 将集合中元素换成拼音
*/
public static List<String> getPinyinList(List<String> list) {
List<String> pinyinList = new ArrayList<String>();
for (Iterator<String> i = list.iterator(); i.hasNext();) {
String str = (String) i.next();
try {
String pinyin = getPinYin(str);
pinyinList.add(pinyin);
} catch (BadHanyuPinyinOutputFormatCombination e) {
e.printStackTrace();
}
}
return pinyinList;
}

public static String getPinYin(String zhongwen)
throws BadHanyuPinyinOutputFormatCombination {

String zhongWenPinYin = "";
// 将中文变成字符数组
char[] chars = zhongwen.toCharArray();

for (int i = 0; i < chars.length; i++) {
String[] pinYin = PinyinHelper.toHanyuPinyinStringArray(chars[i],
getDefaultOutputFormat());
if (pinYin != null) {
zhongWenPinYin += pinYin[0];
} else {
zhongWenPinYin += chars[i];
}
}
return zhongWenPinYin;
}

private static HanyuPinyinOutputFormat getDefaultOutputFormat() {
HanyuPinyinOutputFormat format = new HanyuPinyinOutputFormat();
format.setCaseType(HanyuPinyinCaseType.UPPERCASE);//
format.setToneType(HanyuPinyinToneType.WITHOUT_TONE);//
format.setVCharType(HanyuPinyinVCharType.WITH_U_AND_COLON);//
return format;
}
}

20. 一个应用在桌面显示两个图标
需要在主配置文件中，<application>下。对应的activity

<activity
android:name="a.h.AActivity"
android:label="@string/app_name"
android:theme="@style/Theme.NoDisplay"
android:icon="@drawable/icon">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>

记住两个图标，需要两个activity，中添加这个

<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>配置

21. ScrollView 下只能有一个根布局，不能出现多个.

21. back键点击两次退出应用

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
switch (keyCode) {
case KeyEvent.KEYCODE_BACK:
long secondTime = System.currentTimeMillis();
if (secondTime - firsttime > 2000) { // 如果两次按键时间间隔大于2秒，则不退出
toast(getResources().getString(R.string.exit));
firsttime = secondTime;// 更新firstTime
return true;
} else { // 两次按键小于2秒时，退出应用
finish();
}
break;
}
return super.onKeyUp(keyCode, event);
}

当使用 onBackpress() 方法返回时候无效果