一、 首先Context启动activity可以使用Activity, Service,Receiver, Application;
首先看下Context类结构图：
1， Activity启动不会报以下错：
ERR:android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?
原因：Activity重写了StartActivity方法，在启动的时候没有做限制（具体可以查看下activity的源码）；
2， 其他Context:(会报上面的错误)
其他Context都使用了ContextImp.java中的startActivity(...);
M平台会出错：
@Override
public void startActivity(Intent intent) {
warnIfCallingFromSystemProcess();
startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, Bundle options) {
warnIfCallingFromSystemProcess();
if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
throw new AndroidRuntimeException(
"Calling startActivity() from outside of an Activity "
+ " context requires the FLAG_ACTIVITY_NEW_TASK flag."
+ " Is this really what you want?");
}
mMainThread.getInstrumentation().execStartActivity(
getOuterContext(), mMainThread.getApplicationThread(), null,
(Activity) null, intent, -1, options);
}
N平台不会出错：
@Override
public void startActivity(Intent intent) {
warnIfCallingFromSystemProcess();
startActivity(intent, null);
}
@Override
public void startActivity(Intent intent, Bundle options) {
warnIfCallingFromSystemProcess();
// Calling start activity from outside an activity without FLAG_ACTIVITY_NEW_TASK is
// generally not allowed, except if the caller specifies the task id the activity should
// be launched in.
if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0
&& options != null && ActivityOptions.fromBundle(options).getLaunchTaskId() == -1) {
throw new AndroidRuntimeException(
"Calling startActivity() from outside of an Activity "
+ " context requires the FLAG_ACTIVITY_NEW_TASK flag."
+ " Is this really what you want?");
}
mMainThread.getInstrumentation().execStartActivity(
getOuterContext(), mMainThread.getApplicationThread(), null,
(Activity) null, intent, -1, options);
}
以上就是M和N O 平台的区别。也是在不同平台会报错的原因。
具体activity的启动流程这里不做分析，有兴趣的可以百度下，有好多；