Android 更新UI的幾種方式

一、Activity的 runOnUiThread   

 textView = (TextView) findViewById( R.id.tv );
        new Thread(new Runnable() {
            @Override
            public void run() {

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText( "更新UI了");
                    }
                });
            }
        }).start();

android Activity runOnUiThread() 方法使用

 

二、Handler sendEmptyMessage()

package lib.com.myapplication;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView textView ;

    Handler handler = new Handler( ) {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            textView.setText( "Ui更新了");
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView) findViewById( R.id.tv );
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep( 2000 );
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                handler.sendEmptyMessage( 2 ) ;
            }
        }).start();

    }
}

三、Handler  post()

package lib.com.myapplication;
import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView textView ;

    Handler handler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = (TextView) findViewById( R.id.tv );

        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep( 2000 );
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                handler.post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText( "Ui更新了");
                    }
                }) ;
            }
        }).start();

    }
}

在子線程中切換到主線程

        new Thread(new Runnable() {
            @Override
            public void run() {
                LogUtil.d( "ttt  11111111111" +  Thread.currentThread().getName() );
                new Handler(Looper.getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {
                        LogUtil.d( "ttt  55555555"  +  Thread.currentThread().getName() );
                    }
                });

                LogUtil.d( "ttt  22222222222"  +  Thread.currentThread().getName() );
                LogUtil.d( "ttt  33333333333"  +  Thread.currentThread().getName() );
                LogUtil.d( "ttt  44444444444"  +  Thread.currentThread().getName() );

            }
        }).start();

　　結果

 ttt  11111111111Thread-155
 ttt  22222222222Thread-155
 ttt  33333333333Thread-155
 ttt  44444444444Thread-155
 ttt  55555555main

　　可見這種方式能夠快速切換線程，從log日誌來看，切換到主線程不會阻塞子線程。

 

四、view Post()　

 textView = (TextView) findViewById( R.id.tv );
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep( 2000 );
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                textView.post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText( "Ui更新了");
                    }
                }) ;
            }
        }).start();

總結：

一、其實上面的四種方式均可歸結於一種方式：handler 用於Android線程之間的通訊。

二、爲何android要求只能在UI線程進行UI操做？ 主要仍是爲了不多線程形成的併發的問題。在單線程操做UI是安全的。