Thread中runOnUiThread的简单使用

1.不能在主线程以外操作UI，android中把耗时的操作都放到子线程里面，主线程又叫UI线程

注意：

不要阻塞主线程（UI线程）
不要从主线程以外的线程更新UI（UI线程）

我们看看这个代码

public class FourActivity extends Activity {
    private Button btn;
    private TextView tv;


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

        tv = (TextView) findViewById(R.id.tv_four);
        btn = (Button) findViewById(R.id.btn_four);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(5000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        Toast.makeText(getApplicationContext(), "click button", Toast.LENGTH_SHORT).show();
                    }
                }).start();
            }
        });
    }
}

运行结果是：点击按钮，五秒之后，程序会错误闪退，错误日志为：

05-17 17:41:52.200 28847-28890/com.example.admin.ztest E/AndroidRuntime: FATAL EXCEPTION: Thread-2
    Process: com.example.admin.ztest, PID: 28847
    java.lang.RuntimeException: Can't toast on a thread that has not called Looper.prepare()
        at android.widget.Toast$TN.(Toast.java:397)
        at android.widget.Toast.(Toast.java:117)
        at android.widget.Toast.makeText(Toast.java:280)
        at android.widget.Toast.makeText(Toast.java:270)
        at com.example.admin.ztest.run.FourActivity$1$1.run(FourActivity.java:37)
        at java.lang.Thread.run(Thread.java:764)

2.使用runOnUiThread方法，我们修改一下程序：

package com.example.admin.ztest.run;


import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.example.admin.ztest.R;

public class FourActivity2 extends Activity {
    private Button btn;
    private TextView tv;


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

        tv = (TextView) findViewById(R.id.tv_four);
        btn = (Button) findViewById(R.id.btn_four);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(5000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                Toast.makeText(getApplicationContext(), "FourActivity2 click button", Toast.LENGTH_SHORT).show();
                            }
                        });

                    }
                }).start();
            }
        });
    }
}

这次程序运行正常，点击按钮，五秒以后，正确提示我们的内容。

在这种情况下，可以使用Activity的runOnUiThread方法将toast的显示发布到主线程。 从主线程调用时，runOnUiThread方法立即执行传递的操作，但是当从主线程以外调用时，它会将传递的操作发布到主线程的事件队列。

3.此外，还可以使用控件.post的方式，把消息传递到主线程中

package com.example.admin.ztest.run;


import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.example.admin.ztest.R;

public class FourActivity3 extends Activity {
    private Button btn;
    private TextView tv;


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

        tv = (TextView) findViewById(R.id.tv_four);
        btn = (Button) findViewById(R.id.btn_four);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(5000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                       tv.post(new Runnable() {
                           @Override
                           public void run() {
                               Toast.makeText(getApplicationContext(), "FourActivity3 click button", Toast.LENGTH_SHORT).show();
                               tv.setText("FourActivity3 click button");
                           }
                       });
                    }
                }).start();
            }
        });
    }
}

4.还有一种，最经典的方式，扩展性最好，使用最广泛的，就是Thread+Handler实现异步消息处理

package com.example.admin.ztest.run;


import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.example.admin.ztest.R;

public class FourActivity4 extends Activity {
    private Button btn;
    private TextView tv;

    //这个地方的handler最好封装 防止内存泄漏
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if (msg.what == 100) {
                String res = (String) msg.obj;
                tv.setText(res);
                Toast.makeText(getApplicationContext(), res, Toast.LENGTH_SHORT).show();
            }
        }
    };

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

        tv = (TextView) findViewById(R.id.tv_four);
        btn = (Button) findViewById(R.id.btn_four);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            Thread.sleep(5000); //模拟耗时操作，比如下载
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        Message msg = new Message();
                        msg.what = 100;  //消息发送的标志
                        msg.obj = "FourActivity4 click button"; //消息发送的内容如：  Object String 类 int
                        handler.sendMessage(msg);
                    }
                }).start();
            }
        });
    }
}