在android原生代码中，长按
由此，我们在launcher的代码里面查找一下，首先，我们要找到onLongClick(View v)这个方法，看下代码：
public boolean onLongClick(View v) {
switch (v.getId()) {
case R.id.previous_screen:
if (!isAllAppsVisible()) {
mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,
HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);
showPreviews(v);
}
return true;
case R.id.next_screen:
if (!isAllAppsVisible()) {
mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,
HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);
showPreviews(v);
}
return true;
case R.id.all_apps_button:
if (!isAllAppsVisible()) {
mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,
HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);
showPreviews(v);
}
return true;
在这里只截取了代码中的一部分，我们看到，都调用了showPreviews方法。
private void showPreviews(View anchor) {
showPreviews(anchor, 0, mWorkspace.getChildCount());
}
private void showPreviews(final View anchor, int start, int end) {
final Resources resources = getResources();
final Workspace workspace = mWorkspace;
CellLayout cell = ((CellLayout) workspace.getChildAt(start));
float max = workspace.getChildCount();
final Rect r = new Rect();
resources.getDrawable(R.drawable.preview_background).getPadding(r);
int extraW = (int) ((r.left + r.right) * max);
int extraH = r.top + r.bottom;
int aW = cell.getWidth() - extraW;
float w = aW / max;
int width = cell.getWidth();
int height = cell.getHeight();
int x = cell.getLeftPadding();
int y = cell.getTopPadding();
width -= (x + cell.getRightPadding());
height -= (y + cell.getBottomPadding());
float scale = w / width;
int count = end - start;
final float sWidth = width * scale;
float sHeight = height * scale;
LinearLayout preview = new LinearLayout(this);
PreviewTouchHandler handler = new PreviewTouchHandler(anchor);
ArrayList<Bitmap> bitmaps = new ArrayList<Bitmap>(count);
for (int i = start; i < end; i++) {
ImageView image = new ImageView(this);
cell = (CellLayout) workspace.getChildAt(i);
final Bitmap bitmap = Bitmap.createBitmap((int) sWidth, (int) sHeight,
Bitmap.Config.ARGB_8888);
final Canvas c = new Canvas(bitmap);
c.scale(scale, scale);
c.translate(-cell.getLeftPadding(), -cell.getTopPadding());
cell.dispatchDraw(c);
image.setBackgroundDrawable(resources.getDrawable(R.drawable.preview_background));
image.setImageBitmap(bitmap);
image.setTag(i);
image.setOnClickListener(handler);
image.setOnFocusChangeListener(handler);
image.setFocusable(true);
if (i == mWorkspace.getCurrentScreen()) image.requestFocus();
//添加到LinearLayout中
preview.addView(image,
LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
//最后添加到ArrayList里面去
bitmaps.add(bitmap);
}
//把上面的LinearLayout放到PopupWindow中。
final PopupWindow p = new PopupWindow(this);
p.setContentView(preview);
p.setWidth((int) (sWidth * count + extraW));
p.setHeight((int) (sHeight + extraH));
p.setAnimationStyle(R.style.AnimationPreview);
p.setOutsideTouchable(true);
p.setFocusable(true);
p.setBackgroundDrawable(new ColorDrawable(0));
p.showAsDropDown(anchor, 0, 0);
p.setOnDismissListener(new PopupWindow.OnDismissListener() {
public void onDismiss() {
dismissPreview(anchor);
}
});
anchor.setTag(p);
anchor.setTag(R.id.workspace, preview);
anchor.setTag(R.id.icon, bitmaps);
}
方法一共有三个参数，第一个，被点击的View，第二个从第几个开始，第三个是第几个结束。缩略图是从又向坐开始排列的。
在for循环中，是绘制预览图的代码。
for (int i = start; i < end; i++) {
ImageView image = new ImageView(this);
//获取屏幕
cell = (CellLayout) workspace.getChildAt(i);
//按照上面设定的大小创建一个bitmap
final Bitmap bitmap = Bitmap.createBitmap((int) sWidth, (int) sHeight,
Bitmap.Config.ARGB_8888);
//绘制
final Canvas c = new Canvas(bitmap);
//设置比例
c.scale(scale, scale);
c.translate(-cell.getLeftPadding(), -cell.getTopPadding());
cell.dispatchDraw(c);
//设置image
image.setBackgroundDrawable(resources.getDrawable(R.drawable.preview_background));
image.setImageBitmap(bitmap);
//设置标记
image.setTag(i);
image.setOnClickListener(handler);
image.setOnFocusChangeListener(handler);
image.setFocusable(true);
if (i == mWorkspace.getCurrentScreen()) image.requestFocus();
//添加到LinearLayout中
preview.addView(image,
LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
//最后添加到ArrayList里面去
bitmaps.add(bitmap);
bitmaps.add(bitmap);
}
在源代码中有很多setTag()和getTag()方法，主要用于标记被点击的View，判断跳转事件时，根据tag里面的信息进行相应的跳转。 以上面的代码为例，简单说下setTag()：
<p></p><pre name="code" class="java">image.setTag(i);
image.setOnClickListener(handler);
image.setOnFocusChangeListener(handler);
image.setFocusable(true);
</pre>
<p></p>
<p><span style="font-size:16px">我们找到handler的代码：</span></p>
<p></p>
<pre readonly="" name="code" class="java">class PreviewTouchHandler implements View.OnClickListener, Runnable, View.OnFocusChangeListener {
private final View mAnchor;
public PreviewTouchHandler(View anchor) {
mAnchor = anchor;
}
//响应image的点击事件
public void onClick(View v) {
mWorkspace.snapToScreen((Integer) v.getTag());
v.post(this);
}
public void run() {
dismissPreview(mAnchor);
}
public void onFocusChange(View v, boolean hasFocus) {
if (hasFocus) {
mWorkspace.snapToScreen((Integer) v.getTag());
}
}
}</pre>
<span style="font-size:16px">当点击image,会触发相应事件，然后是获取image中带的信息，然后跳转到相应屏幕。</span>
<p></p>
<pre></pre>
<pre></pre>
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