進度條 ProgressBar
1 常用屬性
style=”?android:attr/progressBarStyleHorizontal” 預設為圓形
android:progress=”33”
android:max=”100”
執行緒休眠
Thread.sleep(100);//拋異常
SystemClock.sleep(100);//不會拋異常

2 執行緒注意事項：
不能在主執行緒中執行耗時的操作，只能在子執行緒中操作
另外，在子執行緒中不能操作主執行緒中的控制元件(ProgressBar除外)

 SubThread->MainThread    錯誤

3 Handler(重點、面試問得比較多)
用於執行緒之間的通訊，比如：主執行緒與子執行緒

.4 執行緒小結
SubThread->MainThread 錯誤
SubThread->Handler->MainThread 正確

public class MainActivity extends AppCompatActivity {
    private ProgressBar pb_main_pb1;
    private int progress=0;
    private TextView tv_main_tv1;
    private MyHandler myHandler=new MyHandler();


    private int
 
 code=1;
    private class MyHandler extends Handler{
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if (code==msg.what){
                progress++;
                pb_main_pb1.setProgress(progress);
                tv_main_tv1.setText(progress+"%"
 
);
            }

        }
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        pb_main_pb1=this.findViewById(R.id.pb_main_pb1);
        tv_main_tv1=this.findViewById(R.id.tv_main_tv1);
    }



    public void setProgress(View view) {
        if (0==progress){
            new MyThread().start();
        }
    }
    private class MyThread extends  Thread{
        @Override
        public void run() {
            super.run();
            while(true){
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (progress==100){
                    progress=0;
                    break;
                }
                Message msg=new Message();
                msg.what=1;
                myHandler.sendMessage(msg);


            }
        }
    }
}