Android之線程回掉更新ui

 

一：工做線程中的回掉更新UI

public class MainActivity extends AppCompatActivity {


    private int i;
    private Callback mCallback;
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.text);
        mCallback = new Callback() {
            @Override
            public void callback(int i) {
                textView.setText("i");
            }
        };
        doWorkAsNewThread(5000,mCallback);
    }

    /**
     * 開啓工做線程
     * @param delayMs 延時，以便對比
     * @param callback 回掉，更新Ui
     */
    private void doWorkAsNewThread(final long delayMs, final Callback callback){
        new Thread(){
            @Override
            public void run() {
                super.run();
                try {
                    Thread.sleep(delayMs);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                do {
                    i++;
                }while(i<100);

                callback.callback(i);
            }
        }.start();
    }
    
    interface Callback{
        void callback(int i);
    }

能夠看到5s後報錯了：Only the original thread that created a view hierarchy can touch its views.

 

二：改造2，在線程裏切換到UI線程回掉

private void doWorkAsNewThread(final long delayMs, final Callback callback){
        new Thread(){
            @Override
            public void run() {
                super.run();
                try {
                    Thread.sleep(delayMs);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                do {
                    i++;
                }while(i<100);
                textView.post(new Runnable() {
                    @Override
                    public void run() {
                        callback.callback(i);
                    }
                });
            }
        }.start();
    }

這樣是可行的，沒報錯。直接在Callback中改也能夠：

mCallback = new Callback() {
            @Override
            public void callback(final int i) {
                textView.post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText(String.valueOf(i));
                    }
                });
            }
        };

可是兩邊都有回掉的話，好像會有問題。

三：異步線程內，用handler去更新是無效的。

 new Handler().post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText(String.valueOf(i));
                    }
                });

 Can't create handler inside thread that has not called Looper.prepare()

加上loop同樣仍是其餘線程。

Looper.prepare();
                new Handler().post(new Runnable() {
                    @Override
                    public void run() {
                        textView.setText(String.valueOf(i));
                    }
                });
                Looper.loop();

四：回掉自行區分選擇在哪一個線程：

private void callbackOnWorkThread(final int i, final Callback callback){
        Looper.prepare();
        new Handler().post(new Runnable() {
            @Override
            public void run() {
                callback.callback(i);
            }
        });
        Looper.loop();
    }

    private void callbackOnMainThread(final int i, final Callback callback){
        new Handler(Looper.getMainLooper()).post(new Runnable() {
            @Override
            public void run() {
                callback.callback(i);
            }
        });
    }