之前的文章写的都是关于Bitmap和内存的优化技术,这一篇文章给大家谈谈Handler。
Handler是Android系统中比较重要的一个知识,在Android多线程面试经常会被问到,在实际项目中的确也经常用到。当然也比较复杂,知识比较多,牵扯到的类有Thread、Looper、Message、MessageQueue。
Android是支持多线程的,通常应用程序中与用户相关的UI事件都是运行在主线程中,比如点击屏幕、按钮等,为了保持主线程顺畅相应用户事件不被阻塞就需要把耗时的操作(主要是联网、操作大文件等)放到子线程中,这个时候你可能会想到Handler(当然还你可以用其他的比如:异步任务,,这个以后再讲),但是Handler又是怎么和Thread联系起来的呢?这个咱们来看一下Android主线程是怎么创建的。
ActivityThread:
在ActivityThread.java中有一个main()函数,这个函数就是在一个应用启动的入口,调用关系是:ActivityManagerService.java中的startProcessLocked函数调用如下代码:
前言:
之前的文章写的都是关于Bitmap和内存的优化技术,这一篇文章给大家谈谈Handler。
Handler是Android系统中比较重要的一个知识,在Android多线程面试经常会被问到,在实际项目中的确也经常用到。当然也比较复杂,知识比较多,牵扯到的类有Thread、Looper、Message、MessageQueue。
Android是支持多线程的,通常应用程序中与用户相关的UI事件都是运行在主线程中,比如点击屏幕、按钮等,为了保持主线程顺畅相应用户事件不被阻塞就需要把耗时的操作(主要是联网、操作大文件等)放到子线程中,这个时候你可能会想到Handler(当然还你可以用其他的比如:异步任务,,这个以后再讲),但是Handler又是怎么和Thread联系起来的呢?这个咱们来看一下Android主线程是怎么创建的。
ActivityThread:
在ActivityThread.java中有一个main()函数,这个函数就是在一个应用启动的入口,调用关系是:ActivityManagerService.java中的startProcessLocked函数调用如下代码:
// Start the process. It will either succeed and return a result containing
// the PID of the new process, or else throw a RuntimeException.
Process.ProcessStartResult startResult = Process.start("android.app.ActivityThread",
app.processName, uid, uid, gids, debugFlags,
app.info.targetSdkVersion, null);
Process.start又做了如下的操作,只看方法注释就行,现在不需要知道具体做了什么:
/**
* Start a new process.
*
* <p>If processes are enabled, a new process is created and the
* static main() function of a <var>processClass</var> is executed there.
* The process will continue running after this function returns.
*
* <p>If processes are not enabled, a new thread in the caller's
* process is created and main() of <var>processClass</var> called there.
*
* <p>The niceName parameter, if not an empty string, is a custom name to
* give to the process instead of using processClass. This allows you to
* make easily identifyable processes even if you are using the same base
* <var>processClass</var> to start them.
*
* @param processClass The class to use as the process's main entry
* point.
* @param niceName A more readable name to use for the process.
* @param uid The user-id under which the process will run.
* @param gid The group-id under which the process will run.
* @param gids Additional group-ids associated with the process.
* @param debugFlags Additional flags.
* @param targetSdkVersion The target SDK version for the app.
* @param zygoteArgs Additional arguments to supply to the zygote process.
*
* @return An object that describes the result of the attempt to start the process.
* @throws RuntimeException on fatal start failure
*
* {@hide}
*/
public static final ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags, int targetSdkVersion,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, targetSdkVersion, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}