Linearlayout getHeight（）返回0但在setOnClickListener内部返回真值[重复]

Question

编辑：本意是问“为什么它在 setOnClickListener 中起作用”，但很快就找到了。 https://stackoverflow.com/a/21926714/6474462

旧： 在玩 ObjectAnimator 时发现 LinearLayout getHeight() 返回 0，但在 setOnClickListener(after click) 内部确实返回了 true 值，这是如何工作的？

    public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final LinearLayout linearLayout = (LinearLayout) findViewById(R.id.main_linear);

        TextView textView1 = (TextView) findViewById(R.id.textview1);
        final TextView textView2 = (TextView) findViewById(R.id.textview2);

        int viewHeight1 = linearLayout.getHeight();
        textView1.setText("viewHeight1: " + viewHeight1);

        textView2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int viewHeight2 = linearLayout.getHeight();
                textView2.setText("viewHeight2: " + viewHeight2);
                }
            });
        }
    }

Answer 1

对象在屏幕上绘制后需要调用 getHeight()

final TextView textView1 = (TextView)findViewById(R.id.textview1);
final ViewTreeObserver object= textView1 .getViewTreeObserver();
   object.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
          textView1 .getHeight()
          object.removeGlobalOnLayoutListener(this);
        }
    });