android studio 55线程更新UI handler

第一步activity-main.xml    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Hello World!"        android:id="@+id/mTxtShowTest"        app:layout_constraintBottom_toBottomOf="parent"        app:layout_constraintLeft_toLeftOf="parent"        app:layout_constraintRight_toRightOf="parent"        app:layout_constraintTop_toTopOf="parent" />    <Button        android:id="@+id/mBtn2"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="Button"        tools:layout_editor_absoluteX="177dp"        tools:layout_editor_absoluteY="595dp" /第二步 MainActivity.javapackage com.example.myhandler2;import androidx.appcompat.app.AppCompatActivity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Button;import android.widget.TextView;public class MainActivity extends AppCompatActivity {    TextView mTxtShowTest;    Button mBtn;    //1、在主线程中通过匿名内部类创建Handler类对象    private Handler mhandler2 =  new Handler(){        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            //执行的UI操作            if (msg.what==1){                mTxtShowTest.setText("匿名内部类方法");                            }        }    };    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mTxtShowTest = (TextView) findViewById(R.id.mTxtShowTest);        mBtn = (Button) findViewById(R.id.mBtn2);        mBtn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                new Thread(new Runnable() {                    @Override                    public void run() {                        // 2、创建所需消息对象                        Message msg = Message.obtain();                        msg.what = 1;                        //3、发送消息                        mhandler2.sendMessage(msg);                    }                    //4、开启线程                }).start();            }        });    }}
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