非静态匿名内部类会保留外部类的引用，可能会导致外部类(如Activity)内存不能正常回收，解决方法：

1.使用非匿名类

private Handler handler = new Handler(new Handler.Callback() {
    public boolean handleMessage(Message msg) {
        if (msg.what == 1) {
            tv2.append((String) msg.obj);
            return true;
        } else {
            tv2.setText("");
            return true;
        }
    }
});

2.使用弱引用

class MainActivityMHandler extends Handler{
    private final WeakReference<MainActivity> mTarget ;

    public MainActivityMHandler(MainActivity act){
        mTarget = new WeakReference<MainActivity>(act);
    }

    public void handleMessage(Message msg) {
        MainActivity act = mTarget.get();
        if(act != null) {
            if (msg.what == 1) {
                act.tv2.append((String) msg.obj);
            } else {
                act.tv2.setText("");
            }
        }
    }
}


private MainActivityMHandler handler = new MainActivityMHandler(this);

3.输入法不显示候选窗，并且显示完成按钮：

android:imeOptions="actionDone"
android:inputType="textNoSuggestions|textVisiblePassword"