activity_logined.xml ui页面
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<ProgressBar
android:id="@+id/pb"
android:layout_width="match_parent"
android:layout_height="wrap_content"
style="@style/Widget.AppCompat.ProgressBar.Horizontal"
android:max="100"
android:min="0"/>
</LinearLayout>
public class LoginedActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_logined);
MyTask myTask = new MyTask();
myTask.execute();//执行异步任务
}
/* 使用AsyncTask模拟下载事件进度条*/
class MyTask extends AsyncTask<Void, Integer, String> {
ProgressBar progressBar;
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected String doInBackground(Void... voids) {//仅此方法加载在子线程中
progressBar = findViewById(R.id.pb);
for (int i = 0; i < 100; i++) {
try {
Thread.sleep(100);
onProgressUpdate(i + 1);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return "加载成功";
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
progressBar.setProgress(values[0]);
}
@Override
protected void onPostExecute(String s) { //耗时操作结束回调方法
super.onPostExecute(s);
progressBar.setVisibility(View.GONE);
Toast.makeText(LoginedActivity.this, s, Toast.LENGTH_SHORT).show();
}
}
}
AsyncTask封装了handler与Thread,更新ui页面只能在主线程中
使用handler与Thread方式较为麻烦,此处仅演示一次消息传送过程
public class MainActivity extends AppCompatActivity {
Button btn;
Handler handler=new Handler(){
@Override
public void handleMessage(@NonNull Message msg) {
super.handleMessage(msg);
if(msg.what==101){
String message= (String) msg.obj;//类型强制转换
btn.setText(message);
}
}
};
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn=findViewById(R.id.btn);
/*线程更改ui的使用 通过Handler*/
new Thread(){
@Override
public void run() {
super.run();
try {
Thread.sleep(10000);
Message message=new Message();
message.what=101;
message.obj="我是消息";
handler.sendMessage(message);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();