Question

编辑：这个问题已经解决了！

我正面临一个希望很简单的问题。当用户点击图像/区域时，我需要在onTouch位置显示/添加图像。这是布局：

activity_test_diff.xml

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".TestDiff"
android:orientation="vertical">

<RelativeLayout
    android:id="@+id/relative_layout"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1">

    <ImageView
        android:id="@+id/img_rectangle"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitCenter"
        android:visibility="invisible"/>

    <ImageView
        android:id="@+id/img_test_diff1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitCenter" />

    <ImageView
        android:id="@+id/click_check_ok"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/check_green_48dp"/>

    <ImageView
        android:id="@+id/click_check_ko"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="gone"
        android:src="@drawable/close_red_48dp"/>

</RelativeLayout>

<ImageView
    android:id="@+id/img_test_diff2"
    android:layout_width="match_parent"
    android:layout_weight="1"
    android:layout_height="0dp"
    android:scaleType="fitCenter"/>
</LinearLayout>

相对布局的父组是一个LinearLayout，但我不在乎是否有人在RelativeLayout之外触摸。这是处理触摸的代码：

TestDiff.java

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test_diff);

    RelativeLayout relative = (RelativeLayout) findViewById(R.id.relative_layout);

    relative.setOnTouchListener(this);
}

@Override
public boolean onTouch(View v, MotionEvent ev) {
    final int action = ev.getAction();

    final int evX = (int) ev.getX();
    final int evY = (int) ev.getY();

    switch (action) {
        case MotionEvent.ACTION_DOWN:

            int x = (int) ev.getX();
            int y = (int) ev.getY();
            RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(
                    RelativeLayout.LayoutParams.WRAP_CONTENT,
                    RelativeLayout.LayoutParams.WRAP_CONTENT);
            ImageView iv = new ImageView(getApplicationContext());
            lp.setMargins(x, y, 0, 0);
            iv.setLayoutParams(lp);
            iv.setImageDrawable(getResources().getDrawable(
                    R.drawable.check_green_48dp));
            ((ViewGroup) v).addView(iv);

            return true;
        case MotionEvent.ACTION_UP:
            // On the UP, we do the click action.
            // The hidden image (img_rectangle) has three different hotspots on it.
            // The colors are red, blue, and yellow.
            // Use img_rectangle to determine which region the user
            return true;
        default:
            return false;
    }
}

这就是即将到来的错误：

Attempt to invoke virtual method 'void android.widget.RelativeLayout.setOnTouchListener(android.view.View$OnTouchListener)' on a null object reference
                                                                       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)

意味着有人可以弄清楚发生了什么！谢谢

Answer 1

你在xml布局上的

：

<RelativeLayout
    android:id="@+id/relative_layout"

你拥有的java代码中的

RelativeLayout relative = (RelativeLayout) findViewById(R.id.layout_relative);

你逆转了亲戚布局词

使用setOnTouchListener在ViewGroup上添加imageView

1 个答案: