我有一个Android应用程序的示例，使用处理程序从工作线程更新主线程上的进度条，它工作正常，但是当我尝试在没有处理程序的工作线程内更新进度条时，它仍然有效，尽管它应该崩溃。因为根据Android文档，UI线程不安全，不能直接从工作线程访问。
***更新 对不起，我把错误的activity_main.xml。 这是我正在使用的正确的。
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.riaz.handlerexample.MainActivity">
<ProgressBar
android:id="@+id/progressBar"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="8dp"
android:layout_marginTop="8dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:indeterminate="false"
android:max="100"
android:progress="0"
android:layout_marginStart="8dp"
android:layout_marginEnd="8dp" />
</android.support.constraint.ConstraintLayout>
***更新
这是activity_main.xml。 **更新。错误的布局文件，请忽略
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ProgressBar
android:id="@+id/progressBar1"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:indeterminate="true"
android:max="10"
android:padding="4dip" >
</ProgressBar>
<TextView
android:id="@+id/tv"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Progress percentage"
android:textSize="16sp"/>
<Button
android:id="@+id/button1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:onClick="startProgress"
android:text="Start"
android:textSize="16sp"/>
</LinearLayout>
Java代码
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ProgressBar;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
Thread thread; // work as a background thread
Handler handler; // handle main thread messages from worker thread
ProgressBar progressBar; // on UI/main thread
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
progressBar = (ProgressBar) findViewById(R.id.progressBar);
Toast.makeText(MainActivity.this, "OnCreate Thread Name = "
+Thread.currentThread().getName(),
Toast.LENGTH_LONG).show(); // Thread Name = main
System.out.println("OnCreate Method,Thread Name= " +
Thread.currentThread().getName()); // Thread Name = main
thread = new Thread( new MyThread());// creating a background thread
thread.start(); // starting the background thread. it will execute run() method in
// MyThread class
handler = new Handler(){ //handles the incoming messages from background thread
@Override // receives message from worker thread sendmessage(message)
public void handleMessage(Message msg) {
System.out.println("Inside Handler,Thread Name= " +
Thread.currentThread().getName()); //thread Name = main
// progressBar.setProgress(msg.arg1);
}
};
}
// this is background / worker thread
class MyThread implements Runnable
{
@Override
public void run() {
Toast.makeText(MainActivity.this, "Worker Thread Name = "
+Thread.currentThread().getName(),
Toast.LENGTH_LONG).show(); // Thread Name = main
for (int i=0; i<100;i++)
{
System.out.println("Worker Thread,Thread Name= " +
Thread.currentThread().getName());
// Message message = Message.obtain(); // blank empty message
// message.arg1 = i;
// handler.sendMessage(message); //calling main thread
progressBar.setProgress(i);
//create delay to see the progress on progressbar
try {
Thread.sleep(300);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}