Android 视图内部 - 自定义视图定位
Android View internal - CustomView positionning
我正在尝试获得有关视图和自定义视图的知识。我阅读了系列文章here, and there。然后我决定看看 Google 如何编码一些视图。
我检索了 LabelView 的代码,并创建了一个包含 RelativLayout 的应用程序,我在其中动态添加了一个(修改后的)LabelView。我正在尝试修改覆盖 setX、setY 的标签的位置。而不是 x, y 作为左上角,我想要 x, y 视图的中心。我所做的不起作用(在下图中,“3”和“30”应该使它们的中心对齐在同一 y)
我添加了一些日志以及提出问题的地方。
- 为什么多次调用measureHeight和measureWidth?
- 为什么 getWidht、getHeight、getRight 和 getBottom 返回 0?
日志下方(我去掉了不相关的):
... I/MainActivity: customLabel.width = 0
... I/MainActivity: customLabel.height = 0
... I/MainActivity: customLabel.getRight = 0
... I/MainActivity: customLabel.getBottom = 0
... I/MainActivity: customLabel2.width = 0
... I/MainActivity: customLabel2.height = 0
... I/MainActivity: customLabel2.getRight = 0
... I/MainActivity: customLabel2.getBottom = 0
...
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
...
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
低于 MainActivity
public class MainActivity extends AppCompatActivity {
private final String TAG = getClass().getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RelativeLayout container = (RelativeLayout) findViewById(R.id.container);
CustomLabelView customLabel = new CustomLabelView(this, "lbl1");
customLabel.setText("3");
customLabel.setX(150);
customLabel.setY(200);
container.addView(customLabel);
Log.i(TAG, "customLabel.width = " + customLabel.getWidth());
Log.i(TAG, "customLabel.height = " + customLabel.getHeight());
Log.i(TAG, "customLabel.getRight = " + customLabel.getRight());
Log.i(TAG, "customLabel.getBottom = " + customLabel.getBottom());
CustomLabelView customLabel2 = new CustomLabelView(this, "lbl2");
customLabel2.setText("66");
customLabel2.setX(450);
customLabel2.setY(200);
customLabel2.setTextSize(80);
container.addView(customLabel2);
Log.i(TAG, "customLabel2.width = " + customLabel2.getWidth());
Log.i(TAG, "customLabel2.height = " + customLabel2.getHeight());
Log.i(TAG, "customLabel2.getRight = " + customLabel2.getRight());
Log.i(TAG, "customLabel2.getBottom = " + customLabel2.getBottom());
}
}
在 LabelView 下方
/*
* based on android-21/legacy/ApiDemos/src/com/example/android/apis/view/LabelView.java
*/
public class CustomLabelView extends View {
private final String TAG = getClass().getSimpleName();
private Paint mTextPaint;
private String mText;
private int mAscent;
//tag to identify instance in log
private String mTag;
/**
* Constructor. This version is only needed if you will be instantiating
* the object manually (not from a layout XML file).
*
* @param context
*/
public CustomLabelView(Context context, String tag) {
super(context);
initLabelView();
mTag = tag;
}
private final void initLabelView() {
mTextPaint = new Paint();
mTextPaint.setAntiAlias(true);
// Must manually scale the desired text size to match screen density
mTextPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
mTextPaint.setColor(0xFF000000);
setPadding(3, 3, 3, 3);
}
/**
* Sets the text to display in this label
*
* @param text The text to display. This will be drawn as one line.
*/
public void setText(String text) {
mText = text;
requestLayout();
invalidate();
}
/**
* Sets the text size for this label
*
* @param size Font size
*/
public void setTextSize(int size) {
// This text size has been pre-scaled by the getDimensionPixelOffset method
mTextPaint.setTextSize(size);
requestLayout();
invalidate();
}
/**
* Sets the text color for this label.
*
* @param color ARGB value for the text
*/
public void setTextColor(int color) {
mTextPaint.setColor(color);
invalidate();
}
/**
* @see android.view.View#measure(int, int)
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(measureWidth(widthMeasureSpec),
measureHeight(heightMeasureSpec));
}
/**
* Determines the width of this view
*
* @param measureSpec A measureSpec packed into an int
* @return The width of the view, honoring constraints from measureSpec
*/
private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text
result = (int) mTextPaint.measureText(mText) + getPaddingLeft()
+ getPaddingRight();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}
Log.i(TAG, "(" + mTag + ") measureWidth: result = " + result);
return result;
}
/**
* Determines the height of this view
*
* @param measureSpec A measureSpec packed into an int
* @return The height of the view, honoring constraints from measureSpec
*/
private int measureHeight(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
mAscent = (int) mTextPaint.ascent();
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text (beware: ascent is a negative number)
result = (int) (-mAscent + mTextPaint.descent()) + getPaddingTop()
+ getPaddingBottom();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}
Log.i(TAG, "(" + mTag + ") measureHeight: result = " + result);
return result;
}
/**
* Render the text
*
* @see android.view.View#onDraw(android.graphics.Canvas)
*/
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawText(mText, getPaddingLeft(), getPaddingTop() - mAscent, mTextPaint);
}
@Override
public void setX(float x) {
float x_center = x + getWidth() / 2;
super.setX(x_center);
super.setX(x_center);
}
@Override
public void setY(float y) {
float y_center = y - getHeight() / 2;
super.setY(y_center);
}
}
Why are measureHeight
and measureWidth
called several time?
measureHeight
和 measureWidth
调用是 onMeasure
回调的结果。
此视图称为“以确定此视图及其所有子视图的大小要求”(阅读更多内容 here)。这基本上意味着当放置此 View
的 View
或 Layout
时,需要知道此 View
的大小要求,这会导致 onMeasure
被调用。
重要的是 它会导致 onMeasure
被调用。它不会直接调用它。你永远不应该自己打电话给 onMeasure
。解释如何调用它的最简单方法是 this View
lifecycle diagram。在 View
上调用 requestLayout
将导致它被调用 onMeasure
。看到你的 CustomLabelView
也在某些方法中调用了它的 requestLayout
。
没有真正的方法来确定 onMeasure
调用的确切数量,因为它会根据您使用的 Layout
类型、您的 View
行为而有所不同和层次结构中的其他 Views'
。
Why are getWidth
, getHeight
, getRight
and getBottom
returning 0?
您正在尝试在 Activity
的 onCreate
中调用它们。这意味着您的 Activity
刚刚被创建,屏幕上还没有绘制任何内容。换句话说,"layout pass" 尚未执行。这基本上意味着您的 CustomLabelView
尚未绘制。如果尚未绘制,则它没有尺寸(这就是为什么所有参数均为 0)。
如果您尝试将以下代码放入 onCreate
中,您可能会得到非 0 值(2 秒后):
final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
Log.i(TAG, "customLabel.width = " + customLabel.getWidth());
Log.i(TAG, "customLabel.height = " + customLabel.getHeight());
Log.i(TAG, "customLabel.getRight = " + customLabel.getRight());
Log.i(TAG, "customLabel.getBottom = " + customLabel.getBottom());
}
}, 2000);
记得将您的 customLabel
标记为 final
。
我正在尝试获得有关视图和自定义视图的知识。我阅读了系列文章here, and there。然后我决定看看 Google 如何编码一些视图。
我检索了 LabelView 的代码,并创建了一个包含 RelativLayout 的应用程序,我在其中动态添加了一个(修改后的)LabelView。我正在尝试修改覆盖 setX、setY 的标签的位置。而不是 x, y 作为左上角,我想要 x, y 视图的中心。我所做的不起作用(在下图中,“3”和“30”应该使它们的中心对齐在同一 y)
我添加了一些日志以及提出问题的地方。
- 为什么多次调用measureHeight和measureWidth?
- 为什么 getWidht、getHeight、getRight 和 getBottom 返回 0?
日志下方(我去掉了不相关的):
... I/MainActivity: customLabel.width = 0
... I/MainActivity: customLabel.height = 0
... I/MainActivity: customLabel.getRight = 0
... I/MainActivity: customLabel.getBottom = 0
... I/MainActivity: customLabel2.width = 0
... I/MainActivity: customLabel2.height = 0
... I/MainActivity: customLabel2.getRight = 0
... I/MainActivity: customLabel2.getBottom = 0
...
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
...
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
... I/CustomLabelView: (lbl2) measureWidth: result = 96
... I/CustomLabelView: (lbl2) measureHeight: result = 99
... I/CustomLabelView: (lbl1) measureWidth: result = 33
... I/CustomLabelView: (lbl1) measureHeight: result = 61
低于 MainActivity
public class MainActivity extends AppCompatActivity {
private final String TAG = getClass().getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RelativeLayout container = (RelativeLayout) findViewById(R.id.container);
CustomLabelView customLabel = new CustomLabelView(this, "lbl1");
customLabel.setText("3");
customLabel.setX(150);
customLabel.setY(200);
container.addView(customLabel);
Log.i(TAG, "customLabel.width = " + customLabel.getWidth());
Log.i(TAG, "customLabel.height = " + customLabel.getHeight());
Log.i(TAG, "customLabel.getRight = " + customLabel.getRight());
Log.i(TAG, "customLabel.getBottom = " + customLabel.getBottom());
CustomLabelView customLabel2 = new CustomLabelView(this, "lbl2");
customLabel2.setText("66");
customLabel2.setX(450);
customLabel2.setY(200);
customLabel2.setTextSize(80);
container.addView(customLabel2);
Log.i(TAG, "customLabel2.width = " + customLabel2.getWidth());
Log.i(TAG, "customLabel2.height = " + customLabel2.getHeight());
Log.i(TAG, "customLabel2.getRight = " + customLabel2.getRight());
Log.i(TAG, "customLabel2.getBottom = " + customLabel2.getBottom());
}
}
在 LabelView 下方
/*
* based on android-21/legacy/ApiDemos/src/com/example/android/apis/view/LabelView.java
*/
public class CustomLabelView extends View {
private final String TAG = getClass().getSimpleName();
private Paint mTextPaint;
private String mText;
private int mAscent;
//tag to identify instance in log
private String mTag;
/**
* Constructor. This version is only needed if you will be instantiating
* the object manually (not from a layout XML file).
*
* @param context
*/
public CustomLabelView(Context context, String tag) {
super(context);
initLabelView();
mTag = tag;
}
private final void initLabelView() {
mTextPaint = new Paint();
mTextPaint.setAntiAlias(true);
// Must manually scale the desired text size to match screen density
mTextPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
mTextPaint.setColor(0xFF000000);
setPadding(3, 3, 3, 3);
}
/**
* Sets the text to display in this label
*
* @param text The text to display. This will be drawn as one line.
*/
public void setText(String text) {
mText = text;
requestLayout();
invalidate();
}
/**
* Sets the text size for this label
*
* @param size Font size
*/
public void setTextSize(int size) {
// This text size has been pre-scaled by the getDimensionPixelOffset method
mTextPaint.setTextSize(size);
requestLayout();
invalidate();
}
/**
* Sets the text color for this label.
*
* @param color ARGB value for the text
*/
public void setTextColor(int color) {
mTextPaint.setColor(color);
invalidate();
}
/**
* @see android.view.View#measure(int, int)
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(measureWidth(widthMeasureSpec),
measureHeight(heightMeasureSpec));
}
/**
* Determines the width of this view
*
* @param measureSpec A measureSpec packed into an int
* @return The width of the view, honoring constraints from measureSpec
*/
private int measureWidth(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text
result = (int) mTextPaint.measureText(mText) + getPaddingLeft()
+ getPaddingRight();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}
Log.i(TAG, "(" + mTag + ") measureWidth: result = " + result);
return result;
}
/**
* Determines the height of this view
*
* @param measureSpec A measureSpec packed into an int
* @return The height of the view, honoring constraints from measureSpec
*/
private int measureHeight(int measureSpec) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
mAscent = (int) mTextPaint.ascent();
if (specMode == MeasureSpec.EXACTLY) {
// We were told how big to be
result = specSize;
} else {
// Measure the text (beware: ascent is a negative number)
result = (int) (-mAscent + mTextPaint.descent()) + getPaddingTop()
+ getPaddingBottom();
if (specMode == MeasureSpec.AT_MOST) {
// Respect AT_MOST value if that was what is called for by measureSpec
result = Math.min(result, specSize);
}
}
Log.i(TAG, "(" + mTag + ") measureHeight: result = " + result);
return result;
}
/**
* Render the text
*
* @see android.view.View#onDraw(android.graphics.Canvas)
*/
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.drawText(mText, getPaddingLeft(), getPaddingTop() - mAscent, mTextPaint);
}
@Override
public void setX(float x) {
float x_center = x + getWidth() / 2;
super.setX(x_center);
super.setX(x_center);
}
@Override
public void setY(float y) {
float y_center = y - getHeight() / 2;
super.setY(y_center);
}
}
Why are
measureHeight
andmeasureWidth
called several time?
measureHeight
和 measureWidth
调用是 onMeasure
回调的结果。
此视图称为“以确定此视图及其所有子视图的大小要求”(阅读更多内容 here)。这基本上意味着当放置此 View
的 View
或 Layout
时,需要知道此 View
的大小要求,这会导致 onMeasure
被调用。
重要的是 它会导致 onMeasure
被调用。它不会直接调用它。你永远不应该自己打电话给 onMeasure
。解释如何调用它的最简单方法是 this View
lifecycle diagram。在 View
上调用 requestLayout
将导致它被调用 onMeasure
。看到你的 CustomLabelView
也在某些方法中调用了它的 requestLayout
。
没有真正的方法来确定 onMeasure
调用的确切数量,因为它会根据您使用的 Layout
类型、您的 View
行为而有所不同和层次结构中的其他 Views'
。
Why are
getWidth
,getHeight
,getRight
andgetBottom
returning 0?
您正在尝试在 Activity
的 onCreate
中调用它们。这意味着您的 Activity
刚刚被创建,屏幕上还没有绘制任何内容。换句话说,"layout pass" 尚未执行。这基本上意味着您的 CustomLabelView
尚未绘制。如果尚未绘制,则它没有尺寸(这就是为什么所有参数均为 0)。
如果您尝试将以下代码放入 onCreate
中,您可能会得到非 0 值(2 秒后):
final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
Log.i(TAG, "customLabel.width = " + customLabel.getWidth());
Log.i(TAG, "customLabel.height = " + customLabel.getHeight());
Log.i(TAG, "customLabel.getRight = " + customLabel.getRight());
Log.i(TAG, "customLabel.getBottom = " + customLabel.getBottom());
}
}, 2000);
记得将您的 customLabel
标记为 final
。