android 应用监听输入法按键事件【比如搜索和回车键等】的整个流程分析

继承于InputMethodService类的服务代码如下：

int keyCode = sKey.getKeyCode();

KeyEvent eDown = new KeyEvent(0, 0, KeyEvent.ACTION_DOWN,
	                        keyCode, 0, 0, 0, 0, KeyEvent.FLAG_SOFT_KEYBOARD);
	                KeyEvent eUp = new KeyEvent(0, 0, KeyEvent.ACTION_UP, keyCode,
	                        0, 0, 0, 0, KeyEvent.FLAG_SOFT_KEYBOARD);

	                onKeyDown(keyCode, eDown);
	                onKeyUp(keyCode, eUp);

上面的代码：把有关按键下发给应用，即应用监听输入法按键事件

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (processKey(event, 0 != event.getRepeatCount())) return true;
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (processKey(event, true)) return true;
        return super.onKeyUp(keyCode, event);
    }

上面的down和up，我们重点看onKeyUp，跟踪下日志，是下面直接返回true了

if (processKey(event, true)) return true;

进入该方法，在该方法里面有如下代码为其覆盖代码：

if (processFunctionKeys(keyCode, realAction)) {
        
            return true;
        }

再进入该方法processFunctionKeys，跟踪其走入了下面代码：

 if (keyCode == KeyEvent.KEYCODE_ENTER) {
            	
               if (!realAction){
                    Log.d(TAG,"processFunctionKeys call KEYCODE_ENTER return");
                    return true;
               }
                sendKeyChar('\n');
                return true;
            }

因为上面realAction为传进来的true，所以执行了如下

sendKeyChar('\n');

进入该方法，该方法在InputMethodService中

    public void sendKeyChar(char charCode) {
        switch (charCode) {
            case '\n': // Apps may be listening to an enter key to perform an action
                if (!sendDefaultEditorAction(true)) {
                    sendDownUpKeyEvents(KeyEvent.KEYCODE_ENTER);
                }
                break;
            default:
                // Make sure that digits go through any text watcher on the client side.
                if (charCode >= '0' && charCode <= '9') {
                    sendDownUpKeyEvents(charCode - '0' + KeyEvent.KEYCODE_0);
                } else {
                    InputConnection ic = getCurrentInputConnection();
                    if (ic != null) {
                        ic.commitText(String.valueOf((char) charCode), 1);
                    }
                }
                break;
        }
    }

因为传进入的是'\n'，所以执行了如下：

case '\n': // Apps may be listening to an enter key to perform an action
                if (!sendDefaultEditorAction(true)) {
                    sendDownUpKeyEvents(KeyEvent.KEYCODE_ENTER);
                }
                break;

看上面注释：// Apps may be listening to an enter key to perform an action，很清楚吧，呵呵，来看看这个方法吧

    public boolean sendDefaultEditorAction(boolean fromEnterKey) {
        EditorInfo ei = getCurrentInputEditorInfo();
        if (ei != null &&
                (!fromEnterKey || (ei.imeOptions &
                        EditorInfo.IME_FLAG_NO_ENTER_ACTION) == 0) &&
                (ei.imeOptions & EditorInfo.IME_MASK_ACTION) !=
                    EditorInfo.IME_ACTION_NONE) {
            // If the enter key was pressed, and the editor has a default
            // action associated with pressing enter, then send it that
            // explicit action instead of the key event.
            InputConnection ic = getCurrentInputConnection();
            if (ic != null) {
                ic.performEditorAction(ei.imeOptions&EditorInfo.IME_MASK_ACTION);
            }
            return true;
        }
        
        return false;
    }

上面这个方法只是通知：让编辑器执行它,表示它可以做一个动作:

 /**
     * Have the editor perform an action it has said it can do.  
     */
    public boolean performEditorAction(int editorAction);

    /**
     * Set of bits in {@link #imeOptions} that provide alternative actions
     * associated with the "enter" key.  This both helps the IME provide
     * better feedback about what the enter key will do, and also allows it
     * to provide alternative mechanisms for providing that command.
     */
    public static final int IME_MASK_ACTION = 0x000000ff;

我们来看这个方法EditableInputConnection中，有关为什么是EditableInputConnection看我之前的帖子就会明白了

    @Override
    public boolean performEditorAction(int actionCode) {
        if (DEBUG) Log.v(TAG, "performEditorAction " + actionCode);
        mTextView.onEditorAction(actionCode);
        return true;
    }

一般应用程序想要监听回车或搜索按键则，如下写法：

edittext.setOnEditorActionListener(new TextView.OnEditorActionListener() {
			
			@Override
			public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
				/*判断是否是“GO”键*/
				if(actionId == EditorInfo.IME_ACTION_GO){							
					
					edittext.setText("success");					
					
					return true;
				}
				return false;
			}
		});

上面这个调用的是TextView中的接口

    /**
     * Interface definition for a callback to be invoked when an action is
     * performed on the editor.
     */
    public interface OnEditorActionListener {
        /**
         * Called when an action is being performed.
         *
         * @param v The view that was clicked.
         * @param actionId Identifier of the action.  This will be either the
         * identifier you supplied, or {@link EditorInfo#IME_NULL
         * EditorInfo.IME_NULL} if being called due to the enter key
         * being pressed.
         * @param event If triggered by an enter key, this is the event;
         * otherwise, this is null.
         * @return Return true if you have consumed the action, else false.
         */
        boolean onEditorAction(TextView v, int actionId, KeyEvent event);
    }

上面的又是怎么实现的呢?

    /**
     * Set a special listener to be called when an action is performed
     * on the text view.  This will be called when the enter key is pressed,
     * or when an action supplied to the IME is selected by the user.  Setting
     * this means that the normal hard key event will not insert a newline
     * into the text view, even if it is multi-line; holding down the ALT
     * modifier will, however, allow the user to insert a newline character.
     */
    public void setOnEditorActionListener(OnEditorActionListener l) {
        if (mInputContentType == null) {
            mInputContentType = new InputContentType();
        }
        mInputContentType.onEditorActionListener = l;
    }

我们看到了OnEditorActionListener l赋值给了mInputContentType.onEditorActionListener

那么我们再回到上面EditableInputConnection中的方法：

    @Override
    public boolean performEditorAction(int actionCode) {
        if (DEBUG) Log.v(TAG, "performEditorAction " + actionCode);
        mTextView.onEditorAction(actionCode);
        return true;
    }

进入如下方法：

mTextView.onEditorAction(actionCode);

   public void onEditorAction(int actionCode) {
        final InputContentType ict = mInputContentType;
        if (ict != null) {
            if (ict.onEditorActionListener != null) {
                if (ict.onEditorActionListener.onEditorAction(this,
                        actionCode, null)) {
                    return;
                }
            }

看到了吧，之前放入mInputContentType的onEditorActionListener现在赋值给了InputContentType ict，然后执行了

ict.onEditorActionListener.onEditorAction(this,
                        actionCode, null)

现在我们明白了吧，搜索和回车等等按键就是这么实现回调的