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Android之Handler

Android 2017/03/07 13:03

Handler的两个主要作用：

1.调度messages和runnables在时间上的执行

2.把一个动作放到一个线程上执行

根本目的就是解决多线程并发的问题

下面我们来写一个例子来更新UI

新建布局文件activity_handler.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_handler"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.cheng.test.HandlerActivity">

<TextView
    android:id="@+id/textView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Hello World!"/>

</LinearLayout>

对应的我们修改HandlerActivity.java的代码，使它实现一秒后更新文本的功能

package com.example.cheng.test;

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

public class HandlerActivity extends AppCompatActivity {
    private TextView textView;
    private Handler handler=new Handler();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler);
        textView=(TextView)findViewById(R.id.textView);
        new Thread(){
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);   
                            textView.setText("更新文本数据");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

运行代码，可以看到程序报错‘只有创建视图层次结构的原始线程可以更改其视图’

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

我们修改HandlerActivity.java的代码

package com.example.cheng.test;

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

public class HandlerActivity extends AppCompatActivity {
    private TextView textView;
    private Handler handler=new Handler();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler);
        textView=(TextView)findViewById(R.id.textView);
        new Thread(){
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);
                    handler.post(new Runnable() {   //将Runnable添加到消息队列
                        @Override
                        public void run() {
                            textView.setText("更新文本数据");
                        }
                    });
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

运行程序，文本被成功的更改了

接下来我们利用Handler来做一个图片轮播

布局文件的代码

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_handler"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.cheng.test.HandlerActivity">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

编写java代码

package com.example.cheng.test;

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

public class HandlerActivity extends AppCompatActivity {

    private ImageView imageView;
    private int images[]={R.drawable.img1,R.drawable.img2,R.drawable.img3};
    private int index;
    private MyRunnable myRunnale=new MyRunnable();
    private Handler handler=new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler);
        imageView=(ImageView)findViewById(R.id.imageView);
        handler.postDelayed(myRunnale,1000);
    }
    class MyRunnable implements Runnable{
        @Override
        public void run() {
            index++;
            index=index%3;
            imageView.setImageResource(images[index]);
            handler.postDelayed(myRunnale,1000);    //将Runnable添加到线程队列中，并在指定时间后运行
        }
    }
}

这样一个轮播就做好，运行程序

方法 解释
post(Runnable) 将Runnable添加到消息队列，runnable将在handler所关联的线程上运行。如果Runnable成功放入到队列，则返回true，否则返回false，通常是因为looper正在退出处理消息队列。
postAtTime(Runnable,long) 将Runnable添加到消息队列，并在指定的时间运行
postDelayed(Runnable,long) 将Runnable添加到消息队列，并在指定时间后运行
sendEmptyMessage(int what) 发送仅包含what值的消息
sendMessage(Message) 将消息添加到消息队列挂起消息队列末尾，它将在handleMessage(Message)中被接收
sendMessageAtTime(Message,long) 将消息在特定时间添加到消息队列挂起消息末尾
sendMessageDelayed(Message,long) 将消息在特定时间后添加到消息队列挂起消息末尾
removeCallbacks() 将Runnable从消息队列中删除，使线程停止运行
obtainMessage() 从全局消息池中获取一个新的消息，比创建分配新的实例更高效
msg.sendToTarget() 将消息发送到消息队列

Message对象携带数据，通常用arg1，arg2来传递消息，还可以传递object对象

MessageQueue就是一个消息队列，可以添加消息，并处理消息

Looper内部包含了一个消息队列MessageQueue，所有的Handler发送的消息都走向这个消息队列。Loooper由系统来控制的循环，一个线程只能有有一个Looper对象。

Looper.Looper方法是一个死循环，不断的从MessageQueue取消息，如果有消息就处理，如果没消息就阻塞

Looper.prepare() 将当前线程初始化为looper。

Looper.loop()在此线程中开始循环处理消息队列，一顶要调用quit()来结束循环

Handler封装了消息的发送，内部会跟Looper进行关联，也就是说在Handler的内部可以找到Looper，找到Looper也就找到了MessageQueue，在Handler中发送消息，其实是向MessageQueue队列中发送消息

Handler负责发送消息，Looper负责接收Handler发送的消息，并直接把消息回传给Handler自己，MessageQueue就是一个存储消息的容器

自定义的与线程相关的Handler

package com.example.cheng.test;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class Handler2Activity extends AppCompatActivity {

    private Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {
            Log.i("UI---",""+Thread.currentThread());
        }
    };

    private  MyThread thread;

    class MyThread extends Thread{

        public Handler handler;
        @Override
        public void run() {
            Looper.prepare();   //将当前线程初始化为looper
            handler=new Handler(){
                @Override
                public void handleMessage(Message msg) {
                    Log.i("---------","currentThread"+Thread.currentThread());
                }
            };
            Looper.loop();    //在此线程中开始循环处理消息队列
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler2);
        thread=new MyThread();
        thread.start();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread.handler.sendEmptyMessage(1);
        handler.sendMessage(Message.obtain());  //将消息添加到消息队列挂起消息队列末尾，它将在handleMessage(Message)中被接收
    }
}

HandlerThread解决多线程并发

package com.example.cheng.test;

import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class ThreadActivity extends AppCompatActivity {

    private HandlerThread thread;
    private Handler handler;

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

        thread=new HandlerThread("handler thread");
        thread.start();
        handler=new Handler(thread.getLooper()){
            @Override
            public void handleMessage(Message msg) {
                Log.i("current thread----->",""+Thread.currentThread());//获取当前正在运行的线程
            }
        };
        handler.sendMessage(Message.obtain());
    }
}

在主线程给子线程发送消息

package com.example.cheng.test;

import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class FourActivity extends AppCompatActivity implements View.OnClickListener{

    //创建主线程的handler
    private Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {
            Message message=new Message();
            Log.i("----","Main Handler");
            //向子线程发送信息
            threadHandler.sendMessageDelayed(message,1000);
        }
    };

    private Handler threadHandler;
    private Button button1;
    private Button button2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_four);
        button1=(Button)findViewById(R.id.button1);
        button2=(Button)findViewById(R.id.button2);
        button1.setOnClickListener(this);
        button2.setOnClickListener(this);
        HandlerThread thread=new HandlerThread("handlerThread");
        thread.start();
        //创建子线程的handler
        threadHandler=new Handler(thread.getLooper()){
            @Override
            public void handleMessage(Message msg) {
                Message message=new Message();
                Log.i("------","thread Handler");
                //向主线程发送信息
                handler.sendMessageDelayed(message,1000);
            }
        };

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.button1:
                handler.sendEmptyMessage(1);
                break;
            case R.id.button2:
                handler.removeMessages(1);
                break;
            default:
                break;
        }
    }
}

更新UI的几种方法

第一种：handler.post

package com.example.cheng.test;

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

public class FiveActivity extends AppCompatActivity {

    private TextView textView;
    private Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {

        }
    };

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

        textView=(TextView)findViewById(R.id.textView);
        new Thread(){
            @Override
            public void run() {
                try {
                    Thread.sleep(2000);

                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            textView.setText("文字已修改");
                        }
                    });

                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

第二种：handler.sendMessage

package com.example.cheng.test;

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

public class FiveActivity extends AppCompatActivity {

    private TextView textView;
    private Handler handler=new Handler(){
        @Override
        public void handleMessage(Message msg) {
            textView.setText("已修改");
        }
    };

    private void handler2(){
        handler.sendMessage(Message.obtain());
    }

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

        textView=(TextView)findViewById(R.id.textView);
        new Thread(){
            @Override
            public void run() {
                try {
                    Thread.sleep(2000);


                    handler2();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

第三种：runOnUiThread

package com.example.cheng.test;

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

public class FiveActivity extends AppCompatActivity {

    private TextView textView;

    private void updateUI(){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                textView.setText("文本已被修改");
            }
        });
    }

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

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

第四种：view.post

package com.example.cheng.test;

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

public class FiveActivity extends AppCompatActivity {

    private TextView textView;

    private void viewUI(){
        textView.post(new Runnable() {
            @Override
            public void run() {
                textView.setText("已修改文本");
            }
        });
    }

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

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

补充

在非UI线程中可以更新UI，因为ViewRootImpl没有实例化时是不会check线程是否为主线程。

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