利用Activity.runOnUiThread(Runnable)把更新ui的代码创建在Runnable中，然后在需要更新ui时，把这个Runnable对象传给Activity.runOnUiThread(Runnable).
Runnable对像就能在ui程序中被调用。
/**
* Runs the specified action on the UI thread. If the current thread is the UI
* thread, then the action is executed immediately. If the current thread is
* not the UI thread, the action is posted to the event queue of the UI thread.
*
* @param action the action to run on the UI thread
*/
public final void runOnUiThread(Runnable action) {
if (Thread.currentThread() != mUiThread) {
mHandler.post(action);
} else {
action.run();
}
}
从上面的源代码中可以看出，程序首先会判断当前线程是否是UI线程，如果是就直接运行，如果不是则post，这时其实质还是使用的Handler机制来处理线程与UI通讯。
private ProgressDialog progressDialog; Context mContext； progressDialog = new ProgressDialog(mContext);
String stri = mContext.getResources().getString(R.string.Is_sending_a_request);
progressDialog.setMessage(stri);
progressDialog.setCanceledOnTouchOutside(false);
progressDialog.show();
new Thread(new Runnable() {
public void run() {
try {
((Activity)mContext).runOnUiThread(new Runnable() {
public void run() {
progressDialog.dismiss();
String s1 = mContext.getResources().getString(R.string.send_successful);
Toast.makeText(mContext, s1, Toast.LENGTH_LONG).show();
}
});
} catch (final Exception e) {
((Activity)mContext).runOnUiThread(new Runnable() {
public void run() {
progressDialog.dismiss();
String s2 = mContext.getResources().getString(R.string.Request_add_buddy_failure);
Toast.makeText(mContext, s2 + e.getMessage(), Toast.LENGTH_LONG).show();
}
});
}
}
}).start();
用这种方式创建ProgressDialog就比较方便，或者刷新adapter也比使用Thread+Handler方便。
如果不是在activity中创建，需要在前面加上((Activity)mContext). 。
来源：https://www.cnblogs.com/tangZH/p/6107556.html