第一步
activity_main.xml
<TextView
android:layout_width="match_parent"
android:id="@+id/text"
android:layout_height="119dp"
android:text="好好學習天天向上!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="@+id/change_text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Button" />
第二步
package com.example.myapplication;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener {
//定義UPDATE_TEXT這個整型敞亮,用於表示更新TextView這個動作
public static final int UPDATE_TEXT = 1;
private TextView text;
private Button changeText;
//創建一個Handler
private Handler handler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case UPDATE_TEXT:
//在這裏可以進行UI操作
//對msg.obj進行String強制轉換
String string=(String)msg.obj;
text.setText(string);
break;
default:
break;
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
text = (TextView) findViewById(R.id.text);
changeText = (Button) findViewById(R.id.change_text);
changeText.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.change_text:
new Thread(new Runnable() {
@Override
public void run() {
//創建一個message
//設置what字段的值爲UPDATE_TEXT,主要是爲了區分不同的message
//設置message.obj的內容
//調用Handler的message對象
//handler中的handlermessage對象是在主線程中運行的
String string="花子凋零水自流";
Message message = new Message();
message.what = UPDATE_TEXT;
message.obj=string;
handler.sendMessage(message);
}
}).start();
break;
default:
break;
}
}
}