onTouch事件传递

来源：互联网发布：长寿行知计算机老师编辑：程序博客网时间：2024/06/04 20:09

前言

在平常开发中，我们经常会遇到点击事件冲突的情况，或者在面试中被问及，那么下面我们来看下onTouch事件到底是怎么回事。

1.代码

先上代码，三个java类和一个简单的xml布局：

父View:

public class ParentView extends LinearLayout {    public ParentView(Context context) {        super(context);    }    public ParentView(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);    }    public ParentView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);    }    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        showLog("--onInterceptTouchEvent--", "--ACTION_DOWN" + "-- result = " + false);        return false;    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "--ACTION_UP()";                break;            default:                tag = "--" + event.getAction();                break;        }        showLog("--dispatchTouchEvent--", tag);        boolean result = super.dispatchTouchEvent(event);        return result;    }    @Override    public boolean onTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "--ACTION_UP()";                break;            default:                tag = "--" + event.getAction();                break;        }        boolean result = super.onTouchEvent(event);        showLog("--onTouchEvent--", tag + "-- result = " +  result);        return result;    }    private void showLog(String method, String msg) {        Log.e("on-touch", "ParentView:" + method + "is called, process:" + msg);    }}

子View:

public class SubView extends View {    public SubView(Context context) {        super(context);    }    public SubView(Context context, @Nullable AttributeSet attrs) {        super(context, attrs);    }    public SubView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "---ACTION_UP()";                break;            default:                tag = "" + event.getAction();                break;        }        showLog("--dispatchTouchEvent--", "event.getAction() = " + event.getAction());        boolean result = super.dispatchTouchEvent(event);        return result;    }    @Override    public boolean onTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "--ACTION_UP()";                break;            default:                tag = "--" + event.getAction();                break;        }        boolean result = super.onTouchEvent(event);        showLog("--onTouchEvent--", tag + "-- result = " + result);        return true;    }    private void showLog(String method, String msg) {        Log.e("on-touch", "SubView:" + method + "is called, process:" + msg);    }}

MainActivity：

public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        findViewById(R.id.parent).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Toast.makeText(MainActivity.this, "父类响应了", Toast.LENGTH_LONG).show();            }        });        findViewById(R.id.sub).setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                Toast.makeText(MainActivity.this, "子类响应了", Toast.LENGTH_LONG).show();            }        });        findViewById(R.id.sub).setOnTouchListener(new View.OnTouchListener() {            @Override            public boolean onTouch(View v, MotionEvent event) {                String tag = "";                switch(event.getAction()) {                    case MotionEvent.ACTION_DOWN:                        tag = "--ACTION_DOWN()";                        break;                    case MotionEvent.ACTION_MOVE:                        tag = "--ACTION_MOVE()";                        break;                    case MotionEvent.ACTION_UP:                        tag = "--ACTION_UP()";                        break;                    default:                        tag = "--" + event.getAction();                        break;                }                showLog("--onTouch--", tag);                return false;            }        });    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "--ACTION_UP()";                break;            default:                tag = "--" + event.getAction();                break;        }        showLog("--dispatchTouchEvent--", tag);        return super.dispatchTouchEvent(event);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        String tag = "";        switch(event.getAction()) {            case MotionEvent.ACTION_DOWN:                tag = "--ACTION_DOWN()";                break;            case MotionEvent.ACTION_MOVE:                tag = "--ACTION_MOVE()";                break;            case MotionEvent.ACTION_UP:                tag = "--ACTION_UP()";                break;            default:                tag = "--" + event.getAction();                break;        }        showLog("--onTouchEvent--", tag);        return super.onTouchEvent(event);    }    private void showLog(String method, String msg) {        Log.e("on-touch", "MainActivity:" + method + "is called, process:" + msg);    }}

都比较简单，只是简单的进行打印事件信息，来确定事件的传递方向。

xml布局：

<?xml version="1.0" encoding="utf-8"?><LinearLayout    xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:gravity="center"    android:orientation="vertical"    >    <com.victor.ontouchdemo.ParentView        android:id="@+id/parent"        android:layout_width="300dp"        android:layout_height="300dp"        android:background="#ff0088"        android:gravity="center"        android:orientation="vertical">        <com.victor.ontouchdemo.SubView            android:id="@+id/sub"            android:layout_width="150dp"            android:layout_height="150dp"            android:background="#000088"/>    </com.victor.ontouchdemo.ParentView></LinearLayout>

也很简单：

2.正常流程分析

如果按照正常流程，不对视图点击事件做任何处理，我们对子View进行点击，那么只有子View会进行响应，而父View不会触发点击事件。

打印信息：

MainActivity:--dispatchTouchEvent is called, process:--ACTION_DOWN()

ParentView:--dispatchTouchEvent is called, process:--ACTION_DOWN()

ParentView:--onInterceptTouchEvent is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent is called, process:event.getAction() = 0

MainActivity:--onTouch is called, process:--ACTION_DOWN()

SubView:--onTouchEvent is called, process:--ACTION_DOWN()-- result = true

MainActivity:--dispatchTouchEvent is called, process:--ACTION_MOVE()

ParentView:--dispatchTouchEvent is called, process:--ACTION_MOVE()

ParentView:--onInterceptTouchEvent is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent is called, process:event.getAction() = 2

MainActivity:--onTouch is called, process:--ACTION_MOVE()

SubView:--onTouchEvent is called, process:--ACTION_MOVE()-- result = true

MainActivity:--dispatchTouchEventiscalled, process:--ACTION_UP()

ParentView:--dispatchTouchEventiscalled, process:--ACTION_UP()

ParentView:--onInterceptTouchEvent()is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEventiscalled, process:event.getAction() = 1

MainActivity:--onTouchiscalled, process:--ACTION_UP()

SubView:--onTouchEventiscalled, process:--ACTION_UP()-- result = true

通过打印的信息，我们发现，事件的传递是由Activity-->父View-->子View的，具体事件的传递是：dispatchTouchEventis-->(onInterceptTouchEvent只有继承自ViewGroup的类才有，如LinearLayout)-->onTouch-->onTouchEvent的。

而onInterceptTouchEvent方法默认是返回false的，也就是父View默认不对子View进行拦截。

默认子View的onTouchEvent会返回true，也就是把点击事件消费了，所以就不会再向父View传递。

而当对子View设置了onTouch事件时，如果没有消费事件，应该返回false，让事件继续传递，此时onTouchEvent会被触发；如果onTouch返回true，则事件被消费，不会再传递给onTouchEvent和父View了。

3.拦截子View事件

如果父View需要拦截子View点击事件，只需要让父View的onInterceptTouchEvent()方法返回true即可。

打印信息：

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN--result = true

ParentView:--onTouchEvent--is called, process:--ACTION_DOWN()-- result = true

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--onTouchEvent--is called, process:--ACTION_MOVE()-- result = true

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--onTouchEvent--is called, process:--ACTION_MOVE()-- result = true

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--onTouchEvent--is called, process:--ACTION_UP()-- result = true

从打印信息我们发现，如果子View的onTouch事件被拦截后，子View的dispatchTouchEvent、onTouch和onTouchEvent都不会再响应了。

4.子View的onTouchEvent或onTouch事件返回false

4.1当onTouch事件返回false，onTouchEvent返回true时，子View能够正常响应点击事件。

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 0

MainActivity:--onTouch--is called, process:--ACTION_DOWN()

SubView:--onTouchEvent--is called, process:--ACTION_DOWN()-- result = true

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 2

MainActivity:--onTouch--is called, process:--ACTION_MOVE()

SubView:--onTouchEvent--is called, process:--ACTION_MOVE()-- result = true

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 1

MainActivity:--onTouch--is called, process:--ACTION_UP()

SubView:--onTouchEvent--is called, process:--ACTION_UP()-- result = true

由打印信息我们可以看到，当onTouch返回false，onTouchEvent返回true照样把事件消费了，不再传递给父View，也就是说，设置onTouch事件，也就是在onTouchEvent事件前，多设置了一层拦截事件而已。

4.2 onTouch事件返回true，onTouchEvent返回false时，子View的onTouchEvent事件不能够正常响应点击事件。因为onTouch事件已经消费了该事件。

MainActivity:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_DOWN()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 0

MainActivity:--onTouch--is called, process:--ACTION_DOWN()
MainActivity:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_MOVE()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 2

MainActivity:--onTouch--is called, process:--ACTION_MOVE()
MainActivity:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--dispatchTouchEvent--is called, process:--ACTION_UP()

ParentView:--onInterceptTouchEvent--is called, process:--ACTION_DOWN-- result = false

SubView:--dispatchTouchEvent--is called, process:event.getAction() = 1

MainActivity:--onTouch--is called, process:--ACTION_UP()

我们看到，当事件传递到onTouch返回true后，onTouchEvent事件并没有执行，因为事件已经被消费了。

4.3 onTouch事件返回false，onTouchEvent返回false