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();            }        });    }}

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