<EditText
            android:id="@+id/message_input"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:imeOptions="actionSend"
            android:inputType="text"
            android:maxLines="1"
            android:singleLine="true" />

android:imeOptions="actionSend" // 起关键作用

 messageInput.setOnEditorActionListener(new TextView.OnEditorActionListener() {
            @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
                if (actionId == EditorInfo.IME_ACTION_SEND) {
                    sendMessage(Body_type.txt, "");
                    return true;
                }
                return false;
            }
        });

键盘显示与隐藏 监听

public class KeyboardStatusDetector {

    KeyboardVisibilityListener visibilityListener;

    boolean keyboardVisible = false;

    public void registerFragment(Fragment f) {
        registerView(f.getView());
    }

    public KeyboardStatusDetector registerActivity(Activity a) {
        return registerView(a.getWindow().getDecorView().findViewById(android.R.id.content));
    }

    public KeyboardStatusDetector registerView(final View v) {
        v.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                Rect r = new Rect();
                v.getWindowVisibleDisplayFrame(r);

                int heightDiff = v.getRootView().getHeight() - (r.bottom - r.top);
                if (heightDiff > 100) { // if more than 100 pixels, its probably a keyboard...
                    /** Check this variable to debounce layout events */
                    if (!keyboardVisible) {
                        keyboardVisible = true;
                        if (visibilityListener != null)
                            visibilityListener.onVisibilityChanged(true);
                    }
                } else {
                    if (keyboardVisible) {
                        keyboardVisible = false;
                        if (visibilityListener != null)
                            visibilityListener.onVisibilityChanged(false);
                    }
                }
            }
        });

        return this;
    }

    public KeyboardStatusDetector setVisibilityListener(KeyboardVisibilityListener listener) {
        visibilityListener = listener;
        return this;
    }

    public static interface KeyboardVisibilityListener {
        public void onVisibilityChanged(boolean keyboardVisible);
    }
}

// 使用：

 View rootView = getWindow().getDecorView().findViewById(android.R.id.content);

        new KeyboardStatusDetector()
                .registerView(rootView)  //or register to an activity
                .setVisibilityListener(new KeyboardStatusDetector.KeyboardVisibilityListener() {
                    @Override
                    public void onVisibilityChanged(boolean keyboardVisible) {
                        if (keyboardVisible) {   // 显示键盘
                           
                        }
                    }
                });