Anndroid學習—使用執行緒 Handler

使用Java裡面常用的執行緒呼叫方式，發現不可以

1 .

package com.example.administrator.myapplication;

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

public class MainActivity extends AppCompatActivity {
 EditText editText;
    Button button;
    Handler handler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText = (EditText) findViewById(R.id.editText2);
        button = (Button) findViewById(R.id.button);
       /* handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
//                super.handleMessage(msg);
                editText.setText("star Thread");
            }
        };*/
 

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                editText.setText("sss");
                MyThread myThread = new MyThread();
                myThread.start();
            }
        });
    }
    class  MyThread extends  Thread{
        @Override
 

        public void run() {
//         super.run();
      editText.setText("star Thread");
           /* try {
            Thread.sleep(6000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }*/
//            handler.sendEmptyMessage(0);
        }
    }
}

2 . 分析錯誤

E/AndroidRuntime: FATAL EXCEPTION: Thread-192
                  Process: com.example.administrator.myapplication, PID: 3528
                  android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
                      at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6357)
                      at android.view.ViewRootImpl.invalidateChildInParent(ViewRootImpl.java:909)
                      at android.view.ViewGroup.invalidateChild(ViewGroup.java:4690)

Android UI操作並不是執行緒安全的並且這些操作必須在UI執行緒中執行，如果在非UI執行緒中直接操作UI執行緒，
會丟擲android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that
created a view hierarchy can touch its views，這與普通的java程式不同。

由於UI執行緒負責事件的監聽和繪圖，因此，必須保證UI執行緒能夠隨時響應使用者的需求，
UI執行緒裡的操作應該向中斷事件那樣短小，費時的操作（如網路連線）需要另開執行緒，
否則，如果UI執行緒超過5s沒有響應使用者請求，會彈出對話方塊提醒使用者終止應用程式（ANP）。
如果在新開的執行緒中需要對UI進行設定，就可能違反單執行緒模型，
因此android採用一種的Message Queue機制保證執行緒間通訊。
可以在自己的子執行緒中建立Handler與UI thread通訊

執行緒的簡單使用-點選按鈕文字框顯示指定內容

package com.example.administrator.myapplication;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
 EditText editText;
    Button button;
    Handler handler;
    MyThread myThread;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText = (EditText) findViewById(R.id.editText2);
        button = (Button) findViewById(R.id.button);
       handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
//                super.handleMessage(msg);
               editText.setText("star Thread");
            }
        };
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                editText.setText("sss");
                 myThread = new MyThread();
                myThread.start();
            }
        });
    }
    class  MyThread extends  Thread{
        @Override
        public void run() {
                while(true){
                try {
                    Thread.sleep(1000);
                    handler.sendEmptyMessage(0);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

用thread handler 實現圖片變換

package com.example.administrator.myapplication;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {
 EditText editText;
    Button button;
    Button button2;
    Handler handler;
    ImageView imageView;
    MyThread myThread;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText = (EditText) findViewById(R.id.editText2);
        button = (Button) findViewById(R.id.button);
        imageView = (ImageView) findViewById(R.id.imageView);
        button2= (Button) findViewById(R.id.button2);

       handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
//                super.handleMessage(msg);
                switch (msg.what){
                    case 1 :
                        imageView.setImageResource(R.mipmap.ic_launcher);
                        break;
                    case  2 :
                        imageView.setImageResource(R.mipmap.abc_ic_star_black_16dp);
                        break;
                }
               // editText.setText("star Thread");

            }
        };
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
//                editText.setText("sss");
                 myThread = new MyThread();
                myThread.is= true;
                myThread.start();
            }
        });
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                myThread.is= false;
            }
        });
    }
    class  MyThread extends  Thread{
        boolean is=true;
        @Override
        public void run() {

            int what = 1;
            while(is){
                try {
                    Thread.sleep(1000);
                    handler.sendEmptyMessage((what++)%2+1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}