android开发常见问题集
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- www.androidkaifa.com提示:Issue意思： 问题，Solution意思：解决方案
- Development
- [Issue] Application crush when return from predefined interface
[Solution 1] You may forgot to call the method of predefined super class
i.e.: In your Activity, if you override onDestroy as following:
class YourActivity extends Activity
{
protected void onDestroy()
{
}
}
when the activity is destroyed, application will crash, in order to resolve this issue, you must modify the code snip to:
class YourActivity extends Activity
{
protected void onDestroy()
{
super.onDestroy(); //Call the same method of super class
}
} - [Issue] Explain view's attributes
android:gravity: Define which direction to align control's contents. - [Issue] How to get and Set system property
[Solution] Use methods System.getProperty(xxx) and System.setProperty(xxx), following properties can be got and set:
java.vendor.url
java.class.path
user.home
java.class.version
os.version
java.vendor
user.dir
user.timezone
path.separator
os.name
os.arch
line.separator
file.separator
user.name
java.version
java.home - [Issue] How to get popular directories and their stat
[Sulotion] Call method android.os.Environment, following directories can be received:
a) root directory
b) external storage directory
c) data directory
d) download cache directory
e) external storage state,
Note: USB mass storage path is /sdcard - [Issue] How to access resource in package in Acrivity
- Get resource value
getResources().getString(resID); //resID looks like R.string.str_id
- Get resource id from name
getResources().getIdentifier("name", "string", getPackageName());
getResources().getIdentifier("name", "drawable", getPackageName()); - [Issue] How to get and set environment variables
[Solution] To get the value of the specified environment variables, just use System.getenv(xxx); But you can't set environment variable in Java code directly, you need to use jni to call C function 'setenv'. - [Issue] How to know byte order of device
[Solution] Call method ByteOrder.nativeOrder(); - [Issue] How to read files in the directories res/raw
[Sulotion]
Resources res = getResources();
InputStream is = res.openRawResource(R.raw.xxx); - [Issue] How to display horizontal bar in widget
[Solution] Use a view which background is filled with the specified color.
<TableLayout xxxxxx>
<TableRow xxxxxx>
......
</TableRow>
......
<View android:layout_height="2dip"
android:background="#FF909090" />
......
</TableLayout>
Comments:
1) A control View with the specified background is shown as a bar
2) The View must be declared within TableLayout
3)If your want to implement the horizontal bar with left/right edgesfading just like ListView's divider, you only need to setandroid:background to "?android:attr/listDivider" - [Issue] How to change contents of TextView
- Set text view to be editable
TextView textView = findViewById(xxx);
textView.setText(textView.getText(), TextView.BufferType.EDITABLE);
- Change contents
textView.setText(xxx);
textView.append(xxx); - [Issue] Customize View
- Define customized view class as following
package com.test.customized;
import xxxxxx;
class CustomizedTextView
{
private static String HEADER = "(Warning)";
private static String RETURN = "\n";
public TextView(Context context)
{
super(context);
}
public TextView(Context context, AttributeSet attrs)
{
super(context, attrs);
}
public TextView(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
}
public void append(CharSequence text, int start, int end)
{
super.append(HEADER, 0, HEADERS.length());
super.append(text, start, end);
super.append(RETURN, 0, RETURN.length());
}
}
- Use the customized view as following
<?xml version="1.0" encoding="utf-8"?>
<com.test.customized.CustomizedTextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="Hello, Android"/> - [Issue] How to use multiple Activity
[Solution] Please refer to:
http://www.apkcn.com/android-80860-1-1.html
http://blog.csdn.net/Class_Raito/archive/2008/11/27/3390737.aspx - [Issue] How to launch activity
[Solution]
Launch application
1) From shell
usage: am [start|instrument]
am start [-a <ACTION>] [-d <DATA_URI>] [-t <MIME_TYPE>]
[-c <CATEGORY> [-c <CATEGORY>] ...]
[-e <EXTRA_KEY> <EXTRA_VALUE> [-e <EXTRA_KEY> <EXTRA_VALUE> ...]
[-n <COMPONENT>] [-D] [<URI>]
am instrument [-e <ARG_NAME> <ARG_VALUE>] [-p <ROF_FILE>]
[-w] <COMPONENT>
For example, launch an application whose manifest are:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="net.xiashou.android">
<application>
<activity>
<intent-filter>
<categoryandroid:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
Command is: #am start -n net.xiashou.android/net.xiashou.android.HelloAndroid
Other usage:
a) Launch browser to open an URI: #am start -a android.intent.action.VIEW -d http://www.xiashou.net
b) Call out: #am start -a android.intent.action.CALL -d tel:10086
c) Launch google map to locate TianJing: #am start -a android.intent.action.VIEWgeo:0,0?q=tianjin
2) From on activate:
Use Intent.
For example, launch an activate whose manifest is:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="koushikdutta.superuser" android:versionCode="1"
android:versionName="1.0.0">
<permission android:name="android.permission.ACCESS_SUPERUSER"
android:label="@string/superuser_permissions_name"
android:description="@string/superuser_permissions_description"
android:protectionLevel="dangerous" />
<application android:icon="@drawable/icon" android:label="@string/app_name"
android:debuggable="true">
<activity android:name=".SuperuserActivity" android:label="Superuser Whitelist">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".SuperuserRequestActivity"
android:label="Superuser" android:permission="android.permission.ACCESS_SUPERUSER">
<intent-filter>
<action android:name="android.intent.action.superuser" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
Launch code is:
Intent intent = new Intent("android.intent.action.superuser");
startActivityForResult(intent, SUPERUSER_REQUEST); - [Issue] How to close current Activity and remove it from Activityhistory stack when you switch to other Activity
[Solution] Call"finish()" in current Activity's methods. - [Issue] How to use class "Cursor"
[Solution] Cursor stores the results of database query, such asContentResolver.query(xxxxx), Cursor contains M(Rows) x N (Columns) eluments,each column has its name and value, we can get them by callinggetColumnName() and getString/getInt()/getLong()/getShort()..... etcrespectively. - [Issue] How to send Http request
[Solution] Use folloing code:
(refer to
http://blog.atrexis.com/index.cfm/2008/6/20/Sending-HTTP-requests-in-Android
http://dotphone.org/redirect.php?tid=33&goto=lastpost
http://dev.shufou.com/?p=28
)
URL url = new URL("www.baidu.com");
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setDoInput(true);
conn.setConnectTimeout(10000);
conn.setRequestMethod(HttpURLConnection.GET);
conn.setRequestProperty("accept", "*/*");
String location = conn.getRequestProperty("location");
int resCode = conn.getResponseCode();
InputStream stream = conn.getInputStream(); - [Issue] Java Network exception
- When establish network connection using socket, SocketException isthrowed, and exception readable string is: "java.net.SocketException:Connection reset".
Solution: add android.permission.INTERNET to application manifest
- Android java.net.SocketException: The connection was reset
Reason: The time out value is too long, try 10 seconds.
- [Issue] Application crush when return from predefined interface