Android初級教程_獲取Android控制元件的寬和高
阿新 • • 發佈：2018-12-24
我們都知道在onCreate()裡面獲取控制元件的高度是0,這是為什麼呢?我們來看一下示例:
首先我們自己寫一個控制元件,這個控制元件非常簡單:
- publicclass MyImageView extends ImageView {
- public MyImageView(Context context, AttributeSet attrs) {
- super(context, attrs);
- }
- public MyImageView(Context context) {
-
super(context);
- }
- @Override
- protectedvoid onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
- super.onMeasure(widthMeasureSpec, heightMeasureSpec);
- System.out.println("onMeasure 我被呼叫了"+System.currentTimeMillis());
- }
- @Override
-
protectedvoid onDraw(Canvas canvas) {
- super.onDraw(canvas);
- System.out.println("onDraw 我被呼叫了"+System.currentTimeMillis());
- }
- }
- <com.test.MyImageView
- android:id="@+id/imageview"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
-
android:src="@drawable/test"/>
測試的Activity的onCreate():
- @Override
- publicvoid onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- System.out.println("執行完畢.."+System.currentTimeMillis());
- }
說明等onCreate方法執行完了,我們定義的控制元件才會被度量(measure),所以我們在onCreate方法裡面通過view.getHeight()獲取控制元件的高度或者寬度肯定是0,因為它自己還沒有被度量,也就是說他自己都不知道自己有多高,而你這時候去獲取它的尺寸,肯定是不行的.
現在碰到這個問題我們不能不解決,在網上找到了如下辦法:
- //------------------------------------------------方法一
- int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
- int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
- imageView.measure(w, h);
- int height =imageView.getMeasuredHeight();
- int width =imageView.getMeasuredWidth();
- textView.append("\n"+height+","+width);
- //-----------------------------------------------方法二
- ViewTreeObserver vto = imageView.getViewTreeObserver();
- vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
- publicboolean onPreDraw() {
- int height = imageView.getMeasuredHeight();
- int width = imageView.getMeasuredWidth();
- textView.append("\n"+height+","+width);
- returntrue;
- }
- });
- //-----------------------------------------------方法三
- ViewTreeObserver vto2 = imageView.getViewTreeObserver();
- vto2.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
- @Override
- publicvoid onGlobalLayout() {
- imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
- textView.append("\n\n"+imageView.getHeight()+","+imageView.getWidth());
- }
- });
這三個方法是哪裡找到現在已經忘了.
現在要討論的是當我們需要時候使用哪個方法呢?
現在把測試的Activity改成如下:
- @Override
- publicvoid onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- final ImageView imageView = (ImageView) findViewById(R.id.imageview);
- //------------------------------------------------方法一
- int w = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
- int h = View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED);
- imageView.measure(w, h);
- int height =imageView.getMeasuredHeight();
- int width =imageView.getMeasuredWidth();
- textView.append("\n"+height+","+width);
- System.out.println("執行完畢.."+System.currentTimeMillis());
- }
接著來看下面幾種方式輸出結果:
把測試Activity改成如下:
- @Override
- publicvoid onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- final ImageView imageView = (ImageView) findViewById(R.id.imageview);
- -----------------------------------------------方法二
- ViewTreeObserver vto = imageView.getViewTreeObserver();
- vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
- publicboolean onPreDraw() {
- int height = imageView.getMeasuredHeight();
- int width = imageView.getMeasuredWidth();
- textView.append("\n"+height+","+width);
- returntrue;
- }
- });
- }
結果如下:
方法三就不再測試了同方法二!!!
那麼方法而和方法三在執行上有什麼區別呢?
我們在佈局檔案中加入一個TextView來記錄這個控制元件的寬高.
- <ScrollView
- android:layout_width="wrap_content"
- android:layout_height="wrap_content" >
- <TextView
- android:id="@+id/text"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content" />
- </ScrollView>
先來測試方法而:
- @Override
- publicvoid onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- final ImageView imageView = (ImageView) findViewById(R.id.imageview);